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Denisyuk, EY (Denisyuk, E. Ya.) Thermodynamics of Deformation and Swelling of Crosslinked Polymers under Small Deformations // POLYMER SCIENCE SERIES A Volume: 54 Issue: 3 Pages: 240-247 MAR 2012

A system of equations and physical relationships that show the quasi-static processes of deformation and swelling of crosslinked polymers in solvents under small deformations of the polymer matrix is proposed. The system is obtained via linearization of the respective equations of the nonlinear theory. This makes it possible to reveal the relationship between the constants of the linear theory and the parameters that characterize the elastic and thermodynamic properties of a solvent-swollen crosslinked polymer under finite deformations. Different types of problems that describe the stress-strain state of inhomogeneously swollen crosslinked polymers, as well as the thermodynamics of their deformation and swelling in a solvent medium, are discussed in terms of the linear theory.

Ames, Nicoli M.; Srivastava, Vikas; Chester, Shawn A.A thermo-mechanically coupled theory for large deformations of amorphous polymers. Part II: Applications //INTERNATIONAL JOURNAL OF PLASTICITY Volume: 25 Issue: 8 Pages: 1495-1539 AUG 2009

We have conducted large-strain compression experiments on three representative amorphous polymeric materials: poly(methyl methacrylate) (PMMA), polycarbonate (PC), and a cyclo-olefin polymer (Zeonex-690R), in a temperature range spanning room temperature to slightly below the glass transition temperature of each material, in a strain rate range of approximate to 10(-4) s(-1) to 10(-1) s(-1), and compressive true strains exceeding 100%. The constitutive theory developed in Part 1 [Anand, L, Ames, N.M., Srivastava, V., Chester, S., 2009. A thermo-mechanically coupled theory for large deformations of amorphous polymers. Part 1: Formulation. International journal of Plasticity] is specialized to capture the salient features of the thermo-mechanically coupled strain rate and temperature dependent large deformation mechanical response of amorphous polymers. For the three amorphous polymers studied experimentally, the specialized constitutive model is shown to perform well in reproducing the following major intrinsic features of the macroscopic stress-strain response of these materials: (a) the strain rate and temperature dependent yield strength; (b) the transient yield-peak and strain-softening which occurs due to deformation-induced disordering; (c) the subsequent rapid strain-hardening due to alignment of the polymer chains at large strains; (d) the unloading response at large strains; and (e) the temperature rise due to plastic-dissipation and the limited time for heat-conduction for the compression experiments performed at strain rates (sic)0.01 s(-1). We have implemented our thermo-mechanically coupled constitutive model by writing a user material subroutine for the finite element program [Abaqus/Explicit. 2007. SIMULIA, Providence, RI]. In order to validate the predictive capabilities of our constitutive theory and its numerical implementation, we have performed the following validation experiments: (i) isothermal fixed-end large-strain reversed-torsion tests on PC; (ii) macro-scale isothermal plane-strain cold- and hot-forming operations on PC; (iii) macro-scale isothermal, axi-symmetric hot-forming operations on Zeonex; (iv) micro-scale hot-embossing of Zeonex: and (v) high-speed normal-impact of a circular plate of PC with a spherical-tipped cylindrical projectile. By comparing the results from this suite of validation experiments of some key macroscopic features, such as the experimentally-measured deformed shapes and the load-displacement curves, against corresponding results from numerical simulations, we show that our theory is capable of reasonably accurately reproducing the experimental results obtained in the validation experiments.

Capaccioli, Simone; Prevosto, Daniele; Lucchesi, Mauro; et al. Relation between configurational entropy and relaxation dynamics of glass-forming systems under volume and temperature reduction Conference: 21st International Congress on Glass and Entropy Location: Trencin, SLOVAKIA Date: JUN 25-27, 2007 //JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 355 Issue: 10-12 Pages: 753-758 MAY 1 2009

The structural relaxation dynamics of two Molecular glass-forming systems have been analyzed by means of dielectric spectroscopy, under cooling and compression conditions. The relation of the dynamic slowing down with the reduction of the configurational entropy, S(c), as predicted by Adam and Gibbs (AG), was also investigated. As S(c) is not directly accessible by experiments. it was estimated, following a common procedure in literature, from the excess entropy S(exc) of the supercooled liquid with respect to the crystal, determined from calorimetric and expansivity measurements over the same T-P range of dynamics investigation. The AG relation, predicting linear dependence between the logarithmic of structural relaxation time and the reciprocal of the product of temperature with configurational entropy, was successfully tested. Actually, a bilinear relation between S(exc) and S(c) was found, with different proportionality factors in isothermal and isobaric conditions. Using Such results, we derived an equation for predicting the pressure dependence of the glass transition temperature, in good accordance with the experimental values in literature.

Capponi, S.; Napolitano, S.; Behrnd, N. R.; Structural Relaxation in Nanometer Thin Layers of Glycerol //JOURNAL OF PHYSICAL CHEMISTRY C Volume: 114 Issue: 39 Pages: 16696-16699 OCT 7 2010

The molecular dynamics in nanometer thin films of glycerol was investigated upon thickness reduction by combining organic molecular deposition with in situ broadband dielectric spectroscopy. Changes in the cooperative dynamics with respect to bulk glycerol were observed for films of thicknesses down to 1.6 nm (corresponding to roughly three molecular layers). Systematic investigation revealed no pure size effects addressable merely to geometrical constraints. However, an increase in the glass transition temperature by 3.5 K was observed for the thinnest film, indicating the presence of a layer with reduced mobility in close proximity to the substrate. The impact of both the upper and lower interfaces has been disentangled by measurements performed during slow desorption. Moreover, proof is given for the existence of a layer with enhanced mobility in the vicinity of the free surface enslaved to the dynamics of the rest of the film.

Deubener, J.; Bornhoeft, H.; Reinsch, S.; Viscosity, relaxation and elastic properties of photo-thermo-refractive glass // JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 355 Issue: 2 Pages: 126-131 JAN 15 2009

Viscometry, ultrasonic echography and mechanical spectroscopy were applied to explore the thermo-mechanical properties of a photo-thermo-refractive (PTR) glass. Newtonian shear viscosity and ultrasonic velocity were used to determine the Maxwell time of structural relaxation. Two fast relaxation modes are found in PTR glass below glass transition temperature, which are attributed to alkali and mixed cation mobility. Respective activation energies, E(gamma) = 72 +/- 4 kJ mol(-1) and E(beta) = 117 +/- 4 kJ mol(-1), are considerably lower than that Of viscous flow at the glass transition E, 465 kJ mol-1 as quantified from mechanical spectroscopy. Decoupling ratios of E(gamma)/E(alpha) = 0.155 and E(beta)J(alpha), = 0.255 are similar to those of sodium trisilicate glass but at considerably longer timescales. These observations imply that beta- and gamma-relaxations are delayed as local structural arrangements are more complex for the multi-component PTR glass.

Fuchs, Britta; Schlenkrich, Felix; Seyffarth, Susanne; et al. Hardening of smooth pulsed laser deposited PMMA films by heating//APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Volume: 98 Issue: 4 Pages: 711-MAR 2010

Smooth poly(methyl methacrylate) (PMMA) films without any droplets were pulsed laser deposited at a wavelength of 248 nm and a laser fluence of 125 mJ/cm(2). After deposition at room temperature, the films possess low universal hardness of only 3 N/mm(2). Thermal treatments up to 200A degrees C, either during deposition or afterwards, lead to film hardening up to values of 200 N/mm(2). Using a combination of complementary methods, two main mechanisms could be made responsible for this temperature induced hardening effect well above the glass transition temperature of 102A degrees C. The first process is induced by the evaporation of chain fragments and low molecular mass material, which are present in the film due to the ablation process, leading to an increase of the average molecular mass and thus to hardening. The second mechanism can be seen in partial cross-linking of the polymer film as soon as chain scission occurs at higher temperatures and the mobility and reactivity of the polymer material is high enough.

Gallego-Gomez, Francisco; Quintana, Jose A.; Villalvilla, Jose M.; et al Phthalocyanines as Efficient Sensitizers in Low-T-g Hole-Conducting Photorefractive Polymer Composites //CHEMISTRY OF MATERIALS Volume: 21 Issue: 13 Pages: 2714-2720 JUL 14 2009

The capability of phthalocyanines (Pc's) to efficiently sensitize low glass transition temperature (T-g) poly(N-vinylcarbazole)-based composites for high-performance photorefractivity (PR) is reported for the First time. Gratings exhibiting total diffraction and two-beam-coupling coefficients as large as 350 cm(-1) are recorded in the millisecond range. The performance is compared to that of standard composites sensitized with C-60 showing advantages like much larger phase-shifts, highly convenient for applications based on optical gain. The dependence of the PR performance on the Pc concentration is studied in detail, revealing that only a very small amount of Pc is needed to obtain high efficiency, which allows us to minimize absorption losses and aggregation. The investigation of two different Pc derivatives provides relevant knowledge to design phthalocyanines with improved sensitization properties.

Gauer, Cornelius; Jia, Zichen; Wu, Hua; Aggregation Kinetics of Coalescing Polymer Colloids//LANGMUIR Volume: 25 Issue: 17 Pages: 9703-9713 SEP 1 2009

The aggregation behavior of a soft, rubbery colloidal system with it relatively low glass transition temperature, T(g) approximate to -20 degrees C. has been investigated. It is found that the average gyration and hydrodynamic radii, < R(g)> and < R(h)>, measured by light scattering techniques, evolve in time in parallel, without exhibiting the crossover typical of rigid particle aggregation. Cryogenic scanning electron microscopy (cryo-SEM) images reveal sphere-like clusters, indicating that complete coalescence between particles occurs during aggregation. Since coalescence leads to a reduction in the total colloidal surface area, the surfactant adsorption equilibrium, and thus the colloidal stability, change in the course of aggregation. It is found that to simulate the observed kinetic behavior based on the population balance equations, it is necessary to assume that all the clusters are spherical and to account for variations in the colloidal stability of each aggregating particle pair with time. This indicates that, fir the given system. the coalescence is very fast, i.e., its time scale is much smaller than that of the aggregation.

Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Thermomechanical behavior of shape memory elastomeric composites//JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Volume: 60 Issue: 1 Pages: 67-83 JAN 2012

Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature (T-g) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it servers as a reversible "switching phase" that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt-crystal transition to achieve the shape memory effect. This potentially allows for material systems and much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behaviour of SMEC. The model is phenomenological, although inspired by micromechanical consideration of load tranfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a temperature change. As such, the composite consists of an elastomer reinforced by a soft liquid at high temperature and a stiff solid at low temperature. The model includes a kinetic description of the non-isothermal crystallization and melting of the fibers during a temperature change. As the fibers tranform from melt to crystal during cooling it is assumed that new crystals are formed in an undeformed state, which requires careful tracking of the kinematics of the evolving phases which comes at a significant computational cost. In order to improve the computational efficiency, an effective phase model (EPM) is adopted to treat the evolving crystal phases as an effective medium. A suite of careful thermomechanical experiments with a SMEC was carried out to calibrate various model parameters, and then to demonstrate the ability of the model to accurately capture the shape memory behavior of the SMEC system during complex thermomechanical loading scenarios. The model also identifies the effects of microstructural design parameters such as the fiber volume fraction.

Goldstein, Martin On the reality of the residual entropy of glasses and disordered crystals: The entropy of mixing // JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 357 Issue: 2 Special Issue: SI Pages: 463-465 JAN 15 2011

We have previously shown that the assumption that the configurational entropy of a supercooled liquid vanishes at; leads to a non-trivial violation of the second law. Here we consider the example of the entropy of mixing. We use as a model system two similar chemical substances which form an ideal solution in a mixed phase. We apply the reasoning of our earlier paper to show that this vanishing would lead to a dilemma; either it violates the second law of thermodynamics, or else it cannot be demonstrated by any conceivable experiment. We show further that the vanishing of the entropy of mixing on kinetic arrest leads to the counter-intuitive result that the chemical potential of each component in an infinitely dilute kinetically arrested (or glassy) solution can equal or the chemical potential of the pure component. The most parsimonious conclusion from these results is that residual entropies are real.

Gonzalez, Maria; Martin-Fabiani, Ignacio; Baselga, Juan; Magnetic nanocomposites based on hydrogenated epoxy resin //MATERIALS CHEMISTRY AND PHYSICS Volume: 132 Issue: 2-3 Pages: 618-624 FEB 15 2012

A hydrogenated derivative of diglycidylether of bisphenol A (HDGEBA) has been successfully employed to prepare magnetic thermosetting nanocomposites. Magnetite nanoparticles of approximate to 110 nm modified with oleic acid were synthesized by co-precipitation of ferric and ferrous salts in ammonium solutions. Nanocomposites with amounts up to 5% w w(-1) of nanoparticles were dispersed in HDGEBA by co-solvent method and cured with m-xylilendiamine. Both the particles and nanocomposites were characterized by FTIR, DSC, TGA, XRD, TEM, DMTA and VSM. Due to the lower polarity of the hydrogenated resin, the enhanced compatibility with magnetite oleic coverage allowed obtaining good dispersions of the nanoparticles for compositions up 1% w w(-1), while at higher concentration agglomerates were observed. Two behaviors in the thermal properties were obtained: for compositions below 1% w w(-1) glass transition temperature increased with the amount of nanoparticles, whereas for higher amounts the glass transition temperature decreased. Superparamagnetic behavior was observed in both the particles and the nanocomposites; the blockage temperature gradually increases with loading but it is lower than the observed for bulk magnetite nanoparticles. This fact reflects that nanoparticle-nanoparticle distances in the nanocomposites gradually decrease with loading which is in accordance with a good dispersion state for low loadings and the presence of aggregates at high loadings.

Gwinner, Michael C.; Khodabakhsh, Saghar; Giessen, Harald;Simultaneous Optimization of Light Gain and Charge Transport in Ambipolar Light-Emitting Polymer Field-Effect Transistors //CHEMISTRY OF MATERIALS Volume: 21 Issue: 19 Pages: 4425-4433 OCT 13 2009

Ambipolar light-emitting field-effect transistors (LEFETs) based oil poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) are able to combine electrical switching capability with the generation of light within a well-defined recombination zone inside the channel. Therefore, they are an attractive architecture not only for low-loss light signal transmission in optoelectronic integrated circuits but also for the potential realization of electrically pumped organic lasers. However, these applications require a Simultaneous optimization of transistor performance and waveguiding of emitted light. Here we show that to achieve efficient waveguiding and optical gain the annealing temperature of the F8BT film has to be kept at 120 degrees C below its glass transition temperature. At such low processing temperatures it is difficult to achieve efficient ambipolar charge injection from gold source/drain electrodes and charge transport at the active transistor interface. We show that modification of the gold electrodes with a 1-decanethiol self-assembled monolayer (SAM) allows efficient charge injection into F8BT films deposited on top. The performance of such ambipolar LEFETs with SAM-modified electrodes is better than that of devices with bare gold electrodes but processed at higher temperatures.

Haroosh, Hazim J.; Dong, Yu; Chaudhary, Deeptangshu S.; et al. Electrospun PLA: PCL composites embedded with unmodified and 3-aminopropyltriethoxysilane (ASP) modified halloysite nanotubes (HNT) // APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Volume: 110 Issue: 2 Pages: 433-442 FEB 2013

Electrospinning is a simple and versatile fiber synthesis technique in which a high-voltage electric field is applied to a stream of polymer melt or polymer solution, resulting in the formation of continuous micro/nanofibers. Halloysite nanotubes (HNT) have been found to achieve improved structural and mechanical properties when embedded into various polymer matrices. This research work focuses on blending poly(epsilon-caprolactone) (PCL) (9 and 15 wt%/v) and poly(lactic acid) (PLA) (fixed at 8 wt%/v) solutions with HNT at two different concentrations 1 and 2 wt%/v. Both unmodified HNT and HNT modified with 3-aminopropyltriethoxysilane (ASP) were utilized in this study. Fiber properties have been shown to be strongly related to the solution viscosity and electrical conductivity. The addition of HNT increased the solution viscosity, thus resulting in the production of uniform fibers. For both PCL concentrations, the average fiber diameter increased with the increasing of HNT concentration. The average fiber diameters with HNT-ASP were reduced considerably in comparison to those with unmodified HNT when using 15 wt%/v PCL. Slightly better dispersion was obtained for PLA: PCL composites embedded with HNT-ASP compared to unmodified HNT. Furthermore, the addition of HNT-ASP to the polymeric blends resulted in a moderate decrease in the degree of crystallinity, as well as slight reductions of glass transition temperature of PCL, the crystallization temperature and melting temperature of PLA within composite materials. The infrared spectra of composites confirmed the successful embedding of HNT-ASP into PLA: PCL nanofibers relative to unmodified HNT due to the premodification using ASP to reduce the agglomeration behavior. This study provides a new material system that could be potentially used in drug delivery, and may facilitate good control of the drug release process.

Huang, Jen-Hsien; Yang, Chuan-Yi; Ho, Zhong-Yo; et al. Annealing effect of polymer bulk heterojunction solar cells based on polyfluorene and fullerene blend //ORGANIC ELECTRONICS Volume: 10 Issue: 1 Pages: 27-33 FEB 2009

Control of blend morphology at the nanoscale and high charge mobility is essential for polymer photovoltaic devices in terms of their power conversion efficiencies (PCE). In the case of bulk heterojunctions solar cells, both blend morphology and charge mobility are influenced by thermal treatment. In this manuscript, we study the effects of annealing temperature on polymer PV devices with blends of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). The morphological changes of blended films were observed upon thermal annealing temperature near and above glass transition temperature (130 degrees C). Such microstructural transformations resulted in modified charge transport pathways and therefore greately influenced the device performance. The highest PCE of 2.14% with an open-circuit voltage (V(OC)) of 0.99 V and a short-circuit current (J(SC)) of 4.24 mA/cm(2) was achieved by device annealing at 70 degrees C for 20 min.

Jia, Xiaolong; Listak, Jessica; Witherspoon, Velencia; Effect of Matrix Molecular Weight on the Coarsening Mechanism of Polymer-Grafted Gold Nanocrystals//LANGMUIR Volume: 26 Issue: 14 Pages: 12190-12197 JUL 20 2010

A systematic evaluation of the effect of polymer matrix molecular weight on the coarsening kinetics of uniformly dispersed polystyrene-grafted gold nanoparticles is presented. Particle coarsening is found to proceed via three stages (i.e., atomic-diffusion-based Ostwald ripening (OR), particle-migration-based collision coalescence, and the subsequent reshaping of particle assemblies). The relative significance of each stage and hence the evolution of particle size and shape have been found to depend sensitively upon time, temperature, and the molecular weight of the host polymer. At temperatures close to the matrix glass-transition temperature, Ostwald ripening has been observed to be dominant on all experimental timescales. With increasing annealing temperature, collision coalescence becomes the dominant mode of coarsening, leading to rapid particle growth. The onset of the latter process is found to be increasingly delayed with increasing molecular weight of the polymer host. Particle coalescence is observed to proceed via two fundamental modes (i.e., diffusion-limited aggregation and growth resulting in the formation of fracial particle clusters and the subsequent recrystallization into more spherical monolithic aggregate structures). Interestingly, particle coarsening in high-molecular-weight matrix polymers is found to proceed significantly faster than predicted on the basis of the bulk polymer viscosity; this acceleration is interpreted to be a consequence of the network characteristics of high-molecular-weight polymers by analogy to the phenomenon of nanoviscosity that has been reported in the context of nanoparticle diffusion within high-molecular-weight polymers

Kappes, Ralf S.; Schoenfeld, Friedhelm; Li, Chen; et al. Temperature analysis of laser heated polymers on microsecond time scales //APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Volume: 106 Issue: 4 Pages: 791-801 MAR 2012

To investigate the temperature profiles on laser heated polymer films, we track the thermal radiation with 1 mu s time and 1 mu m spatial resolution. The resulting two-dimensional temperature graphs are compared to finite element simulations in order to understand the heat conversion and flow. The temperature measurement setup consists of a NIR laser and an optical detection system, which includes high performance optics and a microsecond gated camera, equipped with several interference filters. In this way the thermal radiation is detected in the visible range with spectral resolution. Fitting the spectrum with Planck's law, two-dimensional micrographs of the temperature distribution are obtained. For polystyrene surfaces we were able to analyze the heating and the ablation behavior. Good agreement was found between experimental results and finite element simulations, when ablation is limited to a few tens of nanometers of the film thickness. Ablation of polystyrene starts at 150 degrees C, 50 K above the glass transition temperature. We suggest a photomechanical ablation mechanism at that threshold fluence. For ablation at higher fluence and peak temperature, experiments indicate a thermal decomposition reaction. The temperature range of spinodal decomposition is not reached and can in our case be ruled out as ablation mechanism.

Kim, Hwajeong; Shin, Minjung; Kim, Youngkyoo. Distinct Annealing Temperature in Polymer:Fullerene:Polymer Ternary Blend Solar Cells //JOURNAL OF PHYSICAL CHEMISTRY C Volume: 113 Issue: 4 Pages: 1620-1623 JAN 29 2009

A distinct thermal annealing temperature exhibiting a maximum efficiency was observed for polymer solar cells with a ternary blend film that consists of one soluble fullerene and two kinds of conjugated polymer (electron-donating polymer and electron-accepting polymer). The distinct sharp shape trend of device performance with annealing temperature has been assigned primarily to the influence of the electron-accepting polymer [poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT)], since the glass transition temperature of F8BT was exactly the same as with the best annealing temperature. The performance of the best ternary blend solar cell made in this work was poorer than the well-optimized binary blend with the higher content (donor: acceptor = 1:1) of electron-donating polymer. However, it was slightly better than the comparative binary blend solar cell with the same content of electron-donating polymer (donor:acceptor = 1:2), indicative of further improvement in the performance of ternary blend solar cells through the control of blend composition and/or thickness.

Li, Huawei; Termine, Roberto; Angiolini, Luigi; High T-g, Nonpoled Photorefractive Polymers//CHEMISTRY OF MATERIALS Volume: 21 Issue: 12 Pages: 2403-2409 JUN 23 2009

Room-temperature photorefractivity without prepoling was demonstrated in polymers and copolymers with a glass transition temperature well above 100 degrees C. The compounds used are multifunctional side-chain polymers exhibiting chiral, semiconducting, photochromic, and nonlinear optical (azoaromatic moieties) properties. The photorefractive performance was linked to the reorientational effect of the photogenerated space-charge field, which well below the glass transition temperature can be active in the presence of the conformational mobility achieved via the trans-cis light-induced isomerization. The grating build-up time, which is long at lambda = 633 nm (with a time constant tau approximate to 500-1000 s) decreases by 2 orders of magnitude at lambda = 532 nm, where absorption is higher.

Li, Xi; Zhan, Zai-Ji; Peng, Gui-Rong; New high-performance epoxy nanocomposites co-reinforced by two- and zero-dimensional nanoscale particles //MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Volume: 530 Pages: 680-684 DEC 15 2011

New epoxy nanocomposites co-reinforced by two-dimensional montmorillonite and zero-dimensional nanoSiO(2) were prepared. Mechanical tests and thermal analyses showed that the nanocomposites obtained considerable improvements over neat epoxy in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temperature. (C) 2011 Elsevier B.V. All rights reserved.

Liu, Guodong; Li, Lixia; Zheng, Yang; et al. Temperature gradient in sample and its effect on enthalpy relaxation model fitting of polystyrene // JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 365 Pages: 13-22 APR 1 2013

A method to calculate the temperature profile in the polymer samples in differential scanning calorimetry (DSC) measurements by combining the Fourier's law of heat conduction and structural relaxation model is proposed. It is assumed that the temperature at the bottom of the sample is consistent with the program temperature but temperature lag exists between the top and bottom of the sample because that the thermal transfer paths to the two surfaces of the sample are different. The fitting quality of the apparent heat capacity data of polystyrene (PS) samples with different thicknesses using one set of Tool-Narayanaswamy-Moynihan (TNM) parameters are excellent, which conforms the method for temperature profile calculation. It was found that the temperature gradient has slight effect on the best fit TNM model parameters of PS samples with different thicknesses. The investigation on enthalpy relaxation of PS with different thermal histories showed that the temperature gradient existing in the sample only has slight effect on the thermal history dependence of TNM model parameters, which may originate mainly from the flaw of the model itself.

Luduena, L. N.; Kenny, J. M.; Vazquez, A.; Effect of clay organic modifier on the final performance of PCL/clay nanocomposites//MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Volume: 529 Pages: 215-223 NOV 25 2011

The effect of un-modified and several organo-modified montmorillonites on the morphology, mechanical properties and thermal behavior of polycaprolactone (PCL) based nanocomposites prepared by melt intercalation was studied. The study was centered on the analysis of the clay characteristics that have influence on the final properties of PCL/clay nanocomposites. Polymer/clay compatibility was analyzed studying both bulk and surface polarity degree of the clays by means of water absorption tests (bulk) and contact angle measurements (surface). The thermal stability of the clays was analyzed by dynamic thermogravimetrical tests (TGA). The degradation of the clay organo-modifiers during processing was simulated by isothermal TGA. The clay dispersion degree inside the nanocornposites was analyzed by X-ray diffractometry (XRD). The melt rheology was used as a method to compare the dispersion degree of the clay by means of the shear thinning exponent, n(Rh). The tensile mechanical properties were measured and theoretically analyzed by means of several micro-mechanical models. It was found that the thermal stability of the clay organo-modifiers is a critical factor that can modify the final clay content and the clay dispersion degree inside the nanocomposite, demonstrating that the enhancement of the polymer-clay compatibility may not be the main factor to achieve the best mechanical performance when shear forces during processing, i.e. extrusion techniques, are used to prepare polymer/organo-modified clay nanocomposites.

Mahajan, Dhiraj K.; Estevez, Rafael; Basu, Sumit. Ageing and rejuvenation in glassy amorphous polymers //JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Volume: 58 Issue: 10 Pages: 1474-1488 OCT 2010

Physical ageing of amorphous polymers well below their glass transition temperature leads to changes in almost all physical properties. Of particular interest is the increase in yield stress and post-yield strain softening that accompanies ageing of these materials. Moreover, at larger strain polymers seem to rejuvenate, i.e. aged and non-aged samples have identical stress-strain responses. Also, plastically deforming an aged sample seems to rejuvenate the polymer. In this work we use molecular dynamic simulations with a detailed force field suitable for macromolecular ensembles to simulate and understand the effects of ageing on the mechanical response of these materials. We show that within the timescales of these simulations it is possible to simulate both ageing and rejuvenation. The short range potentials play an important role in ageing and rejuvenation. A typical yield drop exhibited by glassy polymers is a manifestation of a sudden relaxation in the short range structure of an aged polymer. Moreover, the aged polymers are known to be brittle. We show that this is intimately related to its typical stress-strain response which allows it to carry arbitrarily large mean stresses ahead of a notch.

Mikroyannidis, John A.; Tsai, Lin-Ren; Chen, Yun. Synthesis, photophysics and electroluminescence of dendronized styryl-substituted fluorene with triphenylamine units//SYNTHETIC METALS Volume: 159 Issue: 1-2 Pages: 78-84 JAN 2009

Compound 2, a dendronized styryl-substituted fluorene with bulky hole-transporting triphenylamine units, was synthesized by a simple two-step procedure. At the first step of synthesis two triphenylamine units were attached to the C-9 of fluorene while at the second step styryl segments were introduced both on fluorene and triphenylamine by Heck coupling. Compound 2 dissolved in common organic solvents like THF, chloroform, dichloromethane and toluene. This compound was stable up to similar to 320 degrees C and showed high glass transition temperature (T(g)) of 175 degrees C. Compound 2 absorbed around 370 nm with optical band gap of 2.89 eV. It behaved as blue-green light emitter with photoluminescence (PL) emission maximum at 444-465 nm and PL quantum yield of 0.36 in THF solution. The HOMO and LUMO levels of compound 2, estimated from cyclic voltammograms, were -5.20 and -2.40eV, respectively. The electroluminescence (EL) emission maxima (530-570nm) were very different from PL maximum (465nm), which could be explained by the direct cross recombination transition between electrons and holes trapped on triphenylamine subunits. The maximal brightness (current efficiency) of the EL devices (ITO/PEDOT:PSS/2/Ca/Al) was 1348 cd/m(2) (0.12 cd/A) and the color showed obvious blue-shift with an increase in operating voltage.

Ruffino, F.; Torrisi, V.; Marletta, G.; et al. Effects of the embedding kinetics on the surface nano-morphology of nano-grained Au and Ag films on PS and PMMA layers annealed above the glass transition temperature // APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Volume: 107 Issue: 3 Pages: 669-683 JUN 2012

The morphology evolution of nano-grained Ag and Au films deposited on polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymeric layers were studied, using the atomic force microscopy technique, when annealed above the polymers glass transition temperature. The main effects on the morphology changes were identified with those concerning the embedding kinetics of the Ag and Au nanoparticles in the PS or PMMA layers. The embedding process of the nanoparticles follows as a consequence of the long-range mobility of the polymeric chains above the glass transition temperature. In particular, the dependence of the nanoparticles mean height and surface density on the annealing time at various temperatures was quantified. The analyses of these behaviors allowed us: (1) to distinguish the overall embedding process in a first stage in which a thin wetting layer of the polymer coats the nanoparticles followed by a true embedding process of the nanoparticles into the polymer layer; (2) to evaluate the characteristic coating time for the Ag and Au nanoparticles in the PS and PMMA in the first stage; (3) to evaluate the characteristic embedding velocity for the Ag and Au nanoparticles in the PS and PMMA in the second stage; (4) to derive the activation energies for the embedding process of the Ag and Au nanoparticles in PS and PMMA; (5) to identify the embedding statistics of the Ag and Au nanoparticles in PS and PMMA with a "failure" Weibull statistics.

Salamatina, O. B.; Rudnev, S. N.; Bartczak, Z.; et al. Thermodynamics of inelastic deformation of amorphous and crystalline phases in linear polyethylene // POLYMER SCIENCE SERIES A Volume: 53 Issue: 9 Pages: 775-786 SEP 2011

Thermodynamic parameters (work W (def) and heat Q (def)) of inelastic deformation (uniaxial compression up to E >(def) = 50%) are measured for six samples of high-molecular-mass linear PE at room temperature under the regime of active loading. Energy excess Delta U (def) accumulated by the samples subjected to loading are calculated in terms of the first law of thermodynamics. All thermodynamic characteristics linearly increase with crystallinity chi of PE, thus making it possible to extrapolate their values to chi = 0 and 100% and to find the contributions of the amorphous and crystalline phases of the polymer to the overall thermodynamics of deformation. Both of the PE phases contribute to W (def) and Delta U (def), while the crystalline phase alone contributes to heat Q (def). At E > a parts per thousand yen 30%, the energy contribution from the amorphous phase exceeds that from the crystalline phase. A comparison between the plastic behavior of PE crystals and glassy polymers demonstrates that PE crystallites are easier deformed (requires less work W (def)) than glassy polymers. At the same time, the amorphous phase of PE is harder to deform (requires more work W (def) and stores more energy Delta U (def)) than noncrystalline rubbers, apparently because of the deformation of tie chains. The thermodynamic characteristics of deformation are compared for three materials: crystalline metals, PE, and glassy polymers. The similarities and differences in their plastic behaviors are considered.

Sekulic, D. R.; Gordic, M. V.; Djordjevic, I. M.; Irradiation and annealing effects on delamination toughness in carbon/epoxy composite //JOURNAL OF NUCLEAR MATERIALS Volume: 383 Issue: 3 Pages: 209-214 JAN 1 2009

Gamma irradiation to various doses (4.8-27.2 MGy) was performed on unidirectional carbon fiber/epoxy resin composite plates. Unidirectional composite coupons irradiated to various doses were annealed at 180 and 250 degrees C, in vacuum. The strain energy release rate G(IC), as a measure of delamination fracture toughness, was determined by Mode I fracture testing on double cantilever beam coupons. The glass transition temperature (T(g)) of the tested coupons matrices was determined in DMA tests. The effects of irradiation and annealing on G(IC) values - the mean values of 10 propagation points (G(IC),(mean)) and that of fracture initiation (G(IC,init)) - were established. These values were analyzed as a function of irradiation dose and annealing temperatures, having in mind glass transition temperature values changes, as well as the possible mechanisms and phenomena of irradiation and annealing.

Shah, Md. Selim Arif Sher; Basak, Pratyay; Manorama, Sunkara V. Polymer Nanocomposites as Solid Electrolytes: Evaluating Ion Polymer and Polymer-Nanoparticle Interactions in PEG-PU/PAN Semi-IPNs and Titania Systems //JOURNAL OF PHYSICAL CHEMISTRY C Volume: 114 Issue: 33 Pages: 14281-14289 AUG 26 2010

This paper is an investigation on the physicochemical properties and Li ion conductivity behavior of a new class of polymer nanocomposites, which holds promise for its potential use as solid polymer electrolytes (SPE). A family of nanocomposite semi-interpenetrating polymer networks of titania (TiO(2))/poly(ethylene glycol) polyurethane (PEG-PU)/poly(acrylonitrile) (PAN) incorporated with. LiClO(4) was synthesized. The effects of titania loading, nanoparticle surface functionalization, and ion polymer and polymer nanoparticle interactions were evaluated in detail using XRD, FT-IR, TEM, DSC, TG-DTA, and dc conductivity studies. At low degree of TiO2 loading, reasonably good dispersion and encapsulation within the semi-IPN matrix was achieved. FT-IR studies strongly indicate that analogous to the ion polymer interaction, a strong interaction coexists between the polymer matrix (C-O-C) and the surface of TiO(2), nanoparticles. Electron micrographs of the semi-IPN nanocomposite films reveal nanophase separation within the polymer matrix. The larger poly(acrylonitrile) domains (similar to 50-400 nm) along with interspersed titania nanoparticles (similar to 5-20 nm) are well distributed throughout the PEG-PU parent networks. The even dispersion and low nanoparticle agglomeration apparent from the micrographs also indicate a reasonable degree of polymer nanoparticle interaction. Interestingly, no substantial change in the thermal properties of the polymer nanocomposite matrices is observed even with increased amounts of TiO2 loading (up to 5%) and the glass-transition temperature remained well below the ambient (similar to-38 degrees C). The degradation onset temperature for the semi-IPNs and TiO(2) nanocomposites (To similar to 250 degrees C) suggests good thermal stability of the matrix. An enhancement in ionic conductivity for all the semi-IPN/nanocomposite was observed. The presence of a very disordered polymer phase in the near vicinity of the nanoparticle surface, interfacial dynamics possibly creating smaller domains of PEG segments wherein the cations (Li(+)) are more loosely cross-linked under the circumstances of competitive interactions, may help faster ionic transport contributing to the overall increase in the bulk conductivity. Overall, tailoring the polymer nanocomposite matrices further holds promise toward addressing the practical challenges in the success of solid polymer electrolytes in Li(+) ion batteries/dye-sensitized solar cells.

Shepard, Kimberly B.; Guo, Yunlong; Arnold, Craig B.; et al Nanostructured morphology of polymer films prepared by matrix assisted pulsed laser evaporation // APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Volume: 110 Issue: 4 Pages: 771-777 MAR 2013

As recently illustrated, nanostructured glassy polymer films with exceptional thermal and kinetic stability can be formed via Matrix Assisted Pulsed Laser Evaporation (MAPLE) (Guo et al. in Nat. Mater. 11:337, 2012). Relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, glasses prepared by MAPLE can be 40 % less dense and have a 40 K higher glass transition temperature (T (g) ). Furthermore, the kinetic stability in the glassy state can be enhanced by 2 orders-of-magnitude. Here, we examine the stability of the structured morphology. We show that nanostructured glasses may be formed even when the substrate is held at temperatures greater than the polymer T (g) during deposition. In addition, we discuss the origin of the enhanced stability and the mechanism of nanostructured film formation within the framework of the Zhigilei model. Finally, we compare the nanostructured morphology to the surface morphology of other MAPLE-deposited films in the literature.

Shih, Ruey-Sheng; Lu, Chu-Hua; Kuo, Shiao-Wei; Hydrogen Bond-Mediated Self-Assembly of Polyhedral Oligomeric Silsesquioxane-Based Supramolecules //JOURNAL OF PHYSICAL CHEMISTRY C Volume: 114 Issue: 30 Pages: 12855-12862 AUG 5 2010

In this study, a functionalized pentaerythritol star polyester compound [tetrakis(nicotinoxymethyl)methane, TNMM] and an octakis[dimethyl(4-hydroxyphenethyl)siloxy]silsesquioxane (OP-POSS) were synthesized and used as tetrahedral and cubic building blocks, respectively, for three-dimensional, hydrogen-bond-mediated, polyhedral oligomeric silsesquioxane- (POSS-) based supramolecular network structures. With noncovalent chain extension of hydrogen bonds between its pyridine and phenol groups, the PUSS-based supramolecular networks exhibited thermally reversible properties. Compared with the glass transition temperature of OP-POSS (ca. 20 degrees C) and the melting temperature of TNMM (ca. 70 degrees C), the hydrogen-bond-mediated miscible blend of 40 wt % TNMM in OP-POSS exhibited a single and higher glass transition temperature (37 degrees C). Because of its strong intermolecular hydrogen bonding, the dewetting pattern of the blend of 40 wt % TNMM in OP-POSS formed ringlike structures rather than the droplets formed by pure OP-POSS. A transparent, brittle, and glassy solid at room temperature, the blend of 40 wt % TNMM in OP-POSS is an explicit and successful example of a PUSS-based hydrogen-bonded

Sinha, Sudipta Kumar; Chakraborty, Sudip; Bandyopadhyay, Sanjoy Secondary Structure Specific Entropy Change of a Partially Unfolded Protein Molecule // LANGMUIR Volume: 26 Issue: 12 Pages: 9911-9916 JUN 15 2010

The conformational disorder of a protein in its partially unfolded molten globule (MG) form leads to an overall gain in the configurational entropy of the protein molecule. However, considering the differential degree of unfolding of different secondary structural segments of the protein, the entropy gained by them may be nonuniform. In this work, our attempt has been to explore whether any correlation exists between the degree of unfolding of different segments of a protein and their entropy gains. For that, we have carried out atomistic molecular dynamics simulations of the folded native and a partially unfolded structures of the protein villin headpiece subdomain or HP-36 in aqueous medium. It is found that among the three a-helical segments of the protein, the central alpha-helix (helix-2) underwent unfolding during the transition with a consequent entropy gain significantly higher than that of the other two helical segments. The calculations further revealed that the differential entropy gain by the segments of a protein can be used as an effective measure to identify the unfolded segments of the protein and hence to explore the folding pathways.

Smaoui, Hichem; Arous, Mourad; Guermazi, Hajer; et al. Study of relaxations in epoxy polymer by thermally stimulated depolarization current (TSDC) and dielectric relaxation spectroscopy (DRS) // JOURNAL OF ALLOYS AND COMPOUNDS Volume: 489 Issue: 2 Pages: 429-436 JAN 21 2010

Thermally stimulated depolarization current (TSDC) and dielectric relaxation spectroscopy (DRS) techniques were employed to study the relaxations and the conductivity phenomena in epoxy-based polymer. In addition to the primary alpha relaxation process associated with the glass-rubber transition, significant interfacial relaxation and ionic conduction process have been revealed. The ac conductivity is temperature and frequency dependent and shows a dc plateau at low frequencies. Above the glass transition temperature, dc conductivity is described by a Vogel-Tamman-Fulcher-Hesse (VFTH) equation while it shows Arrhenius behaviour at higher temperatures

Song, Xiaomei; Zhao, Yongliang; Wang, Haitao; Fabrication of Polymer Microspheres Using Titania as a Photocatalyst and Pickering Stabilizer //LANGMUIR Volume: 25 Issue: 8 Pages: 4443-4449 APR 21 2009

Facile photocatalytic emulsion polymerization was developed to fabricate polystyrene (PS) microsphere; using a transparent anatase titania hydrosol both as a photocatalyst and stabilizer. Under the appropriate conditions, PS microspheres with a well-defined particle size distribution can be easily produced from 100 to 830 nm. The effects of cross-linking agent ethylene glycol dimethacrylate (EGDMA) and coupling agent acrylic acid (AA) on the particle size and the size distribution of PS microspheres were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and other characterization means. It is proven that EGDMA and AA play importance roles in the morphology of microspheres. In addition, AA bonds a large number of titania nanoparticles on the surface of PS microspheres because its carboxyl group forms inorganic armored polymer microspheres. This interfacial interaction between titania nanoparticles and PS chains causes the elevated glass-transition temperature of microspheres.

Takada, Akira; Conradt, Reinhard; Richet, Pascal Residual entropy and structural disorder in glass: A two-level model and a review of spatial and ensemble vs. temporal sampling //JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 360 Pages: 13-20 JAN 15 2013

As a contribution to the residual entropy debate for glasses, we have made simulations to compare the configurational entropies of a two-level system as calculated from either classical or statistical thermodynamics under equilibrium and nonequilibrium conditions. Upon cooling the latter entropies become greater than the former so that the real residual entropy is greater than the calorimetrically estimated value. We also find that a new equivalent transformation can precisely convert the value of the calorimetric entropy into that of the statistical thermodynamics in our model. New insights on configurational entropy are obtained in terms of 'structural degeneracy' originating from microscopic structural disorder and of macroscopic 'thermodynamic degeneracy' related to the number of microstates included in the most probable macrostate. We refute claims against the 'conventional' view as related to causality and ergodic theory. We also defend the concept of 'spatial sampling' in entropy matters in addition to the traditional 'ensemble' and 'time' samplings. We conclude that the non-zero values of residual entropies do exist and have clear physical and chemical meanings in real crystals and glasses.

Takada, Akira; Conradt, Reinhard; Richet, Pascal Residual entropy and structural disorder in glass: Fluctuation phenomena and time-dependent features as deduced from an Ising-type structural model // JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 365 Pages: 53-58 APR 1 2013

As part of our study of configurational entropy in non-equilibrium systems, we have determined the time-dependent fluctuations in a simple system that undergoes structural transformations similar to those of an Ising model. First, we demonstrate that the calorimetric entropy does approximate the statistical thermodynamic entropy, and that the former reflects the spatial arrangements dealt with by the latter. We then show that neither the assumption of ergodicity nor the use of a canonical ensemble is required to account for non-equilibrium states. We use instead the concept of 'spatial sampling' with which enthalpy, entropy and volume can be defined for each structure at any time. In this way fluctuations of all variables can be calculated without any inconsistency. Finally, we point out that introduction of the new concepts of magnitude and phase factor into configurational entropy can not only explain the existence of residual entropy at 0 K for disordered materials but also allows one to discuss spatially related randomness and kinetically induced fluctuations on an equal footing.

Tanaka, Y.; Yamamoto, T. Enthalpy relaxation of comb-like polymer analysed by combining activation energy spectrum and TNM models // JOURNAL OF NON-CRYSTALLINE SOLIDS Volume: 358 Issue: 14 Pages: 1687-1698 JUL 15 2012

In the enthalpy relaxation of poly(cyanobiphenyl ethylacrylate) (PCB2A), the decrease in enthalpy was measured as a function of ageing time and ageing temperature with DSC technique. Obtained data was analysed at first with the activation energy spectrum (AES) model, then compared with the prediction of a multi-parameter phenomenological model which follows the evolution of the configurational entropy (SC) of the sample during the whole thermal history. In AES model, the decrease in enthalpy is controlled by molecular processes whose energies are distributed over a continuous spectrum. The spectrum gives the relation between the number and energy of processes. In consequence, AES of a single peak was obtained. The energy at which the peak maximum was located decreased with the increase in ageing temperature, which is a well-known behaviour as a distribution of relaxation processes. Furthermore, c(p)(T), the heat capacity data obtained by the calculation based on SC model reproduced the experimental c(p)(T) curve. Model parameters found in the calculation was discussed in relation to the energy value of AES maximum.

Thwala, Justice M.; Goodwin, Jim W.; Mills, Paul D. Rheological Studies of Stability of Colloidal Silica Particles Dispersed in Monoethylene Glycol (MEG) Stabilized by Dodecyl Hexa Ethylene Glycol Monoether (C12E6) // LANGMUIR Volume: 25 Issue: 22 Pages: 12926-12936 NOV 17 2009

The steady shear viscosity, dynamic viscoelasticity, and high shear wave rigidity modulus were measured for silica dispersions stabilized by a nonionic surfactant, dodecyl hexa ethylene glycol monoether (C12E6). Electrokinetic measurements were also obtained to help understand the role of charge on the stability of the silica particles in nonaqueous media. The dispersions were found to be stable at low levels of C12E6 concentrations due to electrostatic repulsions as deduced from zeta potential data. Zeta potentials of silica particles in mono ethylene glycol (MEG) were of the order of (-)20-(-)70 mV, signifying the importance of electrostatic stabilization normally reported in aqueous media. Instability oil further addition of C12E6 to silica particles in MEG, a phenomenon normally obtained with high molecular weight polymers, is explained in terms, of micellar bridging and hydrophobic interactions. The extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is used to model the effect of C12E6 on particle stability. Viscoelasticity of silica in MEG in the presence of C12E6 is also reported. Viscoelasticity was found to be due to weak flocculation resulting in a free energy increase and a decrease in configurational entropy as the dispersion was weakly strained. Viscoelastic measurements are modeled using a mode-coupling model.

Vodnik, Vesna V.; Saponjic, Zoran; Dzunuzovic, Jasna V.; Anisotropic silver nanoparticles as filler for the formation of hybrid nanocomposites //MATERIALS RESEARCH BULLETIN Volume: 48 Issue: 1 Pages: 52-57 JAN 2013

Prismatic and plate-like silver nanoparticles (Ag NPs) were synthesized according to the seed-mediated method. These particles were used as precursors for preparation of homogenous, transparent and colored Ag/poly(vinyl alcohol) (PVA) nanocomposite films with different concentrations of Ag by solution-casting technique. Optical and structural characterization of these nanocomposites includes UV-visible spectroscopy, X-ray diffraction (XRD), FTIR spectroscopy and SEM measurements. Further, the effect of embedded nanoparticles on the thermal properties of the PVA matrix was studied. The value of the glass transition temperature of polymer is found to increase after embedding Ag NPs. Comparison of thermal properties of pure PVA and nanocomposite films showed that the thermo-oxidative stability of polymer slightly increased in the presence of Ag NPs. Furthermore, the effect of the Ag NPs on the crystallinity of polymer was also observed.

Wang, Qingzhou; Lu, Dongmei; Cui, Chunxiang; et al.Fabrication and internal friction behaviors of novel porous CuAlMn shape memory alloy filled with polystyrene //MATERIALS LETTERS Volume: 92 Pages: 82-85 FEB 1 2013

Polystyrene layer with adjustable thickness was introduced into a porous CuAlMn shape memory alloy, and the internal friction behaviors of the resultant materials were investigated using a multifunctional internal friction apparatus through the method of forced vibration. Two relaxational internal friction peaks accompanied by a sharp decrease of the relative dynamic modulus were found at around 95 C and 119 C, respectively. The two internal friction peaks have been ascribed to the relaxation process in a thermal equilibrium state of the polystyrene over its glass transition temperature. The damping capacity of the resultant materials was greatly elevated due to the superposition of several individual damping sources in them.

Wen, Hsin-Yi; Chang, Mei-Ying Synthesis and Characterization of a Blue Light Emitting Material Base on the Spirobifluorene with High Thermal Stability //ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY Volume: 1 Issue: 3 Pages: R103-R107 2012

In this study, we used Suzuki coupling to synthesize 2,2',7,7'-tetrapyren-1-yl-9,9'-spirobifluorene (TPSBF), a blue emitter featuring four identical strongly emitting pyrene units linked around a stable spirobifluorene core. This fluorine derivative exhibits a high fluorescence yield, extreme thermal stability under N-2 (onset decomposition temperature: >540 degrees C), a high glass transition temperature (ca. 240 degrees C), and a stable deep blue emission in the solid state. The presence of the spiro linkage in the structure of TPSBF reduces its tendency to crystallize and increases its glass transition temperature relative to the behavior of the monomeric units. In addition, the tetrahedral nature of the carbon atom at the spiro center preserves the optical and electrochemical characteristics of the pristine pyrene units. A blue organic light emitting diode system by spin-coating process having the configuration indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (50 nm)/polyvinylcarbazole: TPSBF (43%) (90 nm)/4,7-diphenyl-1,10-phenanthroline (30 nm)/LiF (1 nm)/Al (200 nm) exhibited a luminance of 4,130 cd/m(2) at 12 V, Commission Internationale d'Eclairage coordinates of (0.16, 0.16), and current and power efficiencies of 1.9 cd/A and 0.9 lm/W, respectively, at 23 mA/cm(2).

Xiao, ZuoYi; Wang, Anjie; Kim, Dong-Pyo 3D macroporous SiCN ceramic patterns tailored by thermally-induced deformation of template //JOURNAL OF MATERIALS CHEMISTRY Volume: 20 Issue: 14 Pages: 2853-2857 2010

Three-dimensional (3D) macroporous SiCN ceramic patterns with tailored window size and pore shape were fabricated by thermal deformation of a close-packed polystyrene (PS) sphere template, which was obtained by applying consecutive capillary force and centrifugation in a packing process of a few hours. Subsequent infiltration of a viscous preceramic inorganic polymer under strong centrifugal force was followed by pyrolysis at 800 degrees C to decompose the sacrificial PS sphere-packed template. In this work, the window sizes among the interconnected macropores were controlled in the range of 258 to 740 nm by tailoring the shape of the packed PS spheres (diameter 1.5 mu m) by annealing above the glass transition temperature (T(g)) of the PS spheres for different periods. The pore shapes changed from circular to hexagonal, and the BET surface area of the samples was reduced from 443 to 337 m(2) g(-1) with a thinner network skeleton. This approach should be useful in combining a low pressure drop with high external surface area for microfluidic applications with 3D porous structures.

You, Jungmok; Yoon, Jeong Ae; Kim, Jeonghun; et al. Excimer Emission from Self-Assembly of Fluorescent Diblock Copolymer Prepared by Atom Transfer Radical Polymerization //CHEMISTRY OF MATERIALS Volume: 22 Issue: 15 Pages: 4426-4434 AUG 10 2010

Well-defined fluorescent copolymers of methyl methacrylate with 1-pyreneylmethyl methacrylate were synthesized by atom transfer radical polymerization (ATRP). The random and block copolymer could be clearly distinguished by their glass-transition temperature (T(g)) values, with a single T(g) value (124 degrees C) for the random polymer, and two T(g) values (115 and 158 degrees C) for the block copolymer. The emission spectra of the copolymers were different in excimer emission, allowing analysis of the ordering of the two polymers, by determining the ratio between excimer emission (I(E)) and monomer emission (I(M)). The fluorescence spectra of the random copolymer exhibited both monomer and excimer emission of pyrene with a I(E)/I(M) ratio of 1.20-1.39 at a concentration of 0.001-0.05 mg/mL. The block copolymer exhibited strong excimer emission with an emission quantum yield for the excimer (Phi(E)) of 42%. The I(E)/I(M) ratio from the block copolymer was >25, even in a very dilute solution. The Phi(E) value increased to 68% when the block copolymer solution was processed to a thin film, indicating increased interactions among the pyrerie block by self-assembly. In addition, nanopores were formed from the block copolymer, while no specific morphology was found from the random copolymer. The average diameter of the nanopores from block copolymer was similar to 300 nm. Upon thermal annealing of the block copolymer film, a dramatic increase in excimer emission was observed to give a high Phi(E) value of 89%. A face-to-face pyrene assembly in the block copolymer was observed on the high-resolution transmission electron microscopy (HR-TEM) images, from which the average packing period. of the well-defined pyrene block was estimated to range from 4.5 angstrom for pyrene block width to 5.6 angstrom for the width of PMMA mainchain.

Yuan, Qingchun; Cayre, Olivier J.; Fujii, Syuji; Responsive Core-Shell Latex Particles as Colloidosome Microcapsule Membranes//LANGMUIR Volume: 26 Issue: 23 Pages: 18408-18414 DEC 7 2010

Responsive core-shell latex particles are used to prepare colloidosome microcapsules using thermal annealing and internal cross linking of the shell, allowing the production of the microcapsules at high concentrations. The core shell particles are composed of a polystyrene core and a shell of poly[2-(dimethylamino)ethyl methacrylate]-b-poly[methyl methacrylate] (PDMA-b-PMMA) chains adsorbed onto the core surface, providing steric stabilization. The PDMA component of the adsorbed polymer shell confers thermally responsive and pH-responsive characteristics to the latex particle, and it also provides glass transitions at temperatures lower than those of the core and reactive amine groups. These features facilitate the formation of stable Pickering emulsion droplets and the immobilization of the latex particle monolayer on these droplets to form colloidosome microcapsules. The immobilization is achieved through thermal annealing or cross linking of the shell under mild conditions feasible for large-scale economic production. We demonstrate here that it is possible to anneal the particle monolayer on the emulsion drop surface at 75-86 degrees C by using the lower glass-transition temperature of the shell compared to that of the polystyrene cores (similar to 108 degrees C). The colloidosome microcapsules that are formed have a rigid membrane basically composed of a densely packed monolayer of particles. Chemical cross linking has also been successfully achieved by confining a cross linker within the disperse droplet. This approach leads to the formation of single-layered stimulus-responsive soft colloidosome membranes and provides the advantage of working at very high emulsion concentrations because interdroplet cross linking is thus avoided. The porosity and mechanical strength of the microcapsules are also discussed here in terms of the observed structure of the latex particle monolayers forming the capsule membrane.

Zeng, Xiaoliang; Yu, Shuhui; Sun, Rong; Microstructure, thermal and dielectric properties of homogeneous bismaleimide-triazine/barium titanate nanocomposite films //MATERIALS CHEMISTRY AND PHYSICS Volume: 131 Issue: 1-2 Pages: 387-392 DEC 15 2011

Bismaleimide-triazine resin/barium titanate (BT/BaTiO(3)) nanocomposite films were prepared by mixing the nano-BaTiO(3) particles into BT resin, followed by films casting and thermal cure. The surface modification of BaTiO(3) nanoparticles with silane coupling agent results in excellent dispersion and enhances the interaction between BaTiO(3) and the BT matrix. The derived nanocomposite films exhibit improved dielectric constant, while the dielectric loss remains at a low level (<0.05). For the nanocomposite film containing 70 wt% of BaTiO(3), the effective dielectric constant at room temperature reaches 23.63, which is about 7 times larger than that of pure BT resin, and the dielectric loss is only 0.0212 at 100 Hz. The dielectric properties of the nanocomposite films are nearly frequency-independent, which is attributed to the excellent dispersion of BaTiO(3) nanoparticles in the BT matrix. The interaction between BaTiO(3) and BT affects not only the phase transition of BaTiO(3), but also the thermal behavior of BT. Moreover, the nanocomposite films exhibit improved thermal resistance. The highest glass transition temperature (T(g)) is 261 degrees C, indicating good reliability as dielectric materials in applications.

Zhu, Jiahua; Wei, Suying; Chen, Xuelong; Electrospun Polyimide Nanocomposite Fibers Reinforced with Core-Shell Fe-FeO Nanoparticles //JOURNAL OF PHYSICAL CHEMISTRY C Volume: 114 Issue: 19 Pages: 8844-8850 MAY 20 2010

Both pure polyimide (PI) and Fe-FeO nanoparticles reinforced PI nanocomposite fibers with a particle loading of 5, 10, 20, and 30 wt % are produced by electrospinning with optimized operational parameters such as polymer concentration, applied electrical voltage, and tip-to-collector distance. The morphology of the resulting products is correlated to the corresponding rheological behaviors of the pure PI and Fe-FeO/PI nanocomposite solutions. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposite fibers after introducing the Fe-FeO nanoparticles. The glass transition temperature (T(g)) and melting temperature (T(m)) of the nanocomposite fibers increase by 10-12 and 15-17 degrees C, respectively, as compared to those of the pure PI fibers. The magnetic properties of the Fe-FeO nanoparticles in the polymer nanocomposite fibers are different from those of the as-received nanoparticles. An increased shell thickness by 7.4% is deduced after the nanoparticles experiencing the high-voltage electrospinning.

Голованов А.И. КИНЕМАТИКА КОНЕЧНЫХ УПРУГОПЛАСТИЧЕСКИХ ДЕФОРМАЦИЙ// Известия высших учебных заведений. Математика. 2010. № 7. С. 16-30

Дается обзор различных подходов, используемых при разложении полных деформаций на упругие и неупругие (пластические) компоненты при мультипликативном представлении тензора градиента деформаций. Кратко описывается кинематика конечных деформаций и произвольных течений. Показывается, что произведения главных значений тензоров искажения упругих и пластических деформаций определяют главные значения тензора искажения полных деформаций. При разложении деформаций и их скоростей на упругую и неупругую составляющие описываются две группы способов: первая предполагает аддитивное разложение специальным образом построенных тензоров, определенных в едином базисе (исходном, текущем или "промежуточном"), вторая - использование некоторого соотношения, связывающего тензоры, описывающие упругие и пластические деформации. Приводится пример построения определяющих соотношений упругопластической среды при больших деформациях из уравнений термодинамики.


Предложена система уравнений и физических соотношений, описывающих квазистатические процессы деформирования и набухания сетчатых полимеров в растворителях при малых деформациях полимерной матрицы. Она получена путем линеаризации соответствующих уравнений нелинейной теории. Это позволило установить связь констант линейной теории с параметрами, характеризующими упругие и термодинамические свойства набухшего в растворителе сетчатого полимера при конечных деформациях. В рамках линейной теории рассмотрены различные типы задач, описывающих напряженно-деформированное состояние неоднородно набухших сетчатых полимеров, а также термодинамику их деформирования и набухания в среде растворителя.

Косарев А.В., Студенцов В.Н. СТАТИСТИЧЕСКАЯ ТЕРМОДИНАМИКА ДЕФОРМАЦИИ СЕТЧАТОГО ПОЛИМЕРА//Пластические массы. 2009. № 2. С. 40-42.

Косарев А.В., Студенцов В.Н.УЧЕТ СТРУКТУРНОГО ФАКТОРА В ЗАДАЧЕ МОДЕЛИРОВАНИЯ УПРУГО?ДЕФОРМАЦИОННЫХ СВОЙСТВ ГУСТОСШИТОГО ПОЛИМЕРА//Бюллетень медицинских интернет-конференций. 2012. Т. 2. № 4. С. 201-202

В статье предложен математический подход, позволяющий охарактеризовать пространственную организацию межузловых цепей в ячейке густосшитого полимера. Введена функция распределения конформации и проведен ее анализ в отсутствии и в присутствии деформирующих возмущений. В рамках подхода статистической термодинамики получены уравнения для энтропии деформации в густосшитом полимере, а также выражения для упруго- деформационных характеристик полимера: работы деформации, напряжения и модуля упругости.

Манцыбора А.А., Русанов М.М. АВТОМОДЕЛЬНАЯ ЗАДАЧА О ДИНАМИКЕ РАЗГРУЗКИ УПРУГОПЛАСТИЧЕСКОГО ПОЛУПРОСТРАНСТВА//Сибирский журнал индустриальной математики. 2013. Т. XVI. № 2 (54). С. 122-129

Приведено решение плоской автомодельной задачи о ступенчатом высокоскоростном снятии нагружающих усилий с границы упругопластического полупространства со значительным уровнем накопленных необратимых деформаций. Однозначность в совокупности возникающих волн разгрузки (простые волны или плоские разрывы) основывается на законах термодинамики и условиях эволюционности распространяющихся разрывов деформаций.

Метлов Л.С., Давиденко А.А. АНАЛИЗ КРИВЫХ УПРОЧНЕНИЯ, ПОЛУЧЕННЫХ В ПРОЦЕССЕ ИПД// Вестник Тамбовского университета. Серия: Естественные и технические науки. 2013. Т. 18. № 4-2. С. 1964-1965.

Проведено сравнение теоретических, рассчитанных в рамках метода неравновесной эволюционной термодинамики, и экспериментальных кривых упрочнения материалов, подвергнутых обработке интенсивной пластической деформацией. Показано, что эти кривые практически могут быть совмещены подбором масштабов по вертикальной и горизонтальной оси. В рамках трехуровневой модели показано, что процесс накопления микротрещин может привести к деградации материала и к его разупрочнению.

Метлов Л.С., Пашинская Е.Г. НЕРАВНОВЕСНАЯ ЭВОЛЮЦИОННАЯ ТЕРМОДИНАМИКА КОМБИНИРОВАННОЙ ДЕФОРМАЦИИ //Вестник Тамбовского университета. Серия: Естественные и технические науки. 2010. Т. 15. № 3-1n. С. 967-968

Подход неравновесной эволюционной термодинамики развит с учетом тензорного характера структурных дефектов. Работа выполнена при частичной поддержке русско-украинского проекта Ф28/443-2009 ДФФД и РФФД.

Пааш Г., Графов Б.М. ТЕРМОДИНАМИКА ПОВЕРХНОСТНОЙ УПРУГОСТИ//Электрохимия. 2009. Т. 45. № 1. С. 78-86.

В настоящей работе обобщена и расширена серия статей о термодинамике поверхностной упругости. В ее основе лежит учет конечной величины упругой деформации. Он приводит к обобщенному виду уравнений для поверхностного избытка внутренней энергии, адсорбционного уравнения Гиббса и уравнения Шаттельворта. Во всех случаях существуют поправочные члены, содержащие тензор деформаций. Хотя деформация может быть мала, эти поправки критичны для получения производных по деформации, которые необходимы для получения уравнений, связывающих между собой измеряемые величины. Эти заключения подробно продемонстрированы для простого случая сферического электрода. При традиционной электрохимической обработке данных плотности экстенсивных величин относят к деформированной поверхности, о чем обычно умалчивают. По аналогии с теорией объемной упругости, в которой плотности относят к недеформированному твердому телу, можно и плотности поверхностных избыточных величин относить к недеформированной поверхности. Такая формулировка дает прежде всего дополнительное доказательство правильности некоторых обобщенных уравнений. Более того, в рамках этого подхода можно выразить поверхностный избыток плотности энергии через поверхностную работу недеформированной поверхности и три константы поверхностной упругости, две из которых – это поверхностные константы Ламе. В альтернативном подходе уравнение Шаттельворта получается просто как соотношение между обобщенной силой и обобщенным потенциалом.


Дано обоснование концепции физической мезомеханики о том, что в основе нелинейного поведения твердых тел при их пластической деформации и разрушении лежит возникновение в локальных сильнонеравновесных зонах наноструктурных состояний. Их структурные превращения или двухфазный распад определяют неравновесную термодинамику зарождения деформационных дефектов и трещин. Обсуждаются нелинейные волновые механизмы влияния наноструктурных состояний на пластическую деформацию и разрушение твердых тел.

Петушков В.А., Надарейшвили А.И. ОБОБЩЕННАЯ ГРАДИЕНТНАЯ МОДЕЛЬ ЗАКРИТИЧЕСКОГО ПОВЕДЕНИЯ ТВЕРДОГО ТЕЛА С УЧЕТОМ МАСШТАБНОГО ПАРАМЕТРА//Проблемы машиностроения и автоматизации. 2012. № 1. С. 139-145

В статье описываются основные, экспериментально наблюдаемые явления закритического деформирования твердого тела. С позиции законов термодинамики представлены определяющие соотношения предлагаемой обобщенной физико-механической модели среды при конечных деформациях. В модели включены такие регуляторы корректности краевой задачи, как вязкость среды, градиенты второго порядка от внутренних переменных системы и масштабный параметр (характеристическая длина) структуры среды, а также микроструктурная модель кинетики повреждаемости.

Сагдатуллин М.К. ПОСТАНОВКА ЗАДАЧИ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ КОНЕЧНЫХ ДЕФОРМАЦИЙ МКЭ// Вестник Казанского технологического университета. 2013. Т. 16. № 5. С. 210-215

В работе излагаются основы методики численного исследования конечных деформаций изотропных гиперупругих тел, ориентированной на применение МКЭ. Первый раздел посвящен кинематике конечных деформаций в Лагранжевой системе координат, вводятся тензоры и меры деформации, определяющих скорости, приведены различные тензоры напряжений. Во втором разделе формулируются физические соотношения гиперупругой изотропной среды, используя уравнения термодинамики. В третьем разделе приводится разрешающее линеаризованное уравнение в текущей конфигурации и выводятся соотношения, определяющие скорость изменения тензора напряжения Коши-Эйлера как линейной функции от тензора пространственного градиента скорости.

Саламатина О.Б., Руднев С.Н., Bartczak Z., Олейник Э.Ф. ТЕРМОДИНАМИКА НЕУПРУГОЙ ДЕФОРМАЦИИ АМОРФНОЙ И КРИСТАЛЛИЧЕСКОЙ ФАЗ ЛИНЕЙНОГО ПОЛИЭТИЛЕНА//Высокомолекулярные соединения. 2011. Т. 53. № 9. С. 1524-1536.

Измерены термодинамические параметры (работа Wдеф и теплота Qдеф) неупругой деформации (одноосное сжатие до деф = 50%) шести образцов линейного высокомолекулярного полиэтилена при комнатной температуре и активном нагружении. Изменение энергии образцов при деформации Uдеф вычислено из первого закона термодинамики. Все термодинамические характеристики линейно растут со степенью кристалличности полиэтилена, что позволило экстраполировать их значения к = 0 и 100% и определить вклад аморфной и кристаллической фаз в термодинамику деформации материала. В работу Wдеф и Uдеф вносят вклад обе фазы полиэтилена, а в теплоту Qдеф – только кристаллическая фаза. При 30% энергетический вклад аморфной фазы становится больше, чем кристаллической. Сравнение пластического поведения кристаллов полиэтилена и стеклообразных полимеров показывает, что кристаллическая фаза полиэтилена пластически деформируется легче (требует меньше Wдеф), чем стеклообразные полимеры. В то же время аморфная фаза деформируется труднее (требует больших Wдеф и запасает больше Uдеф), чем не содержащие кристаллов каучуки, что, по-видимому, связано с деформацией проходных цепей. Проведено сравнение термодинамики деформации трех материалов – кристаллических металлов, полиэтилена и стеклообразных полимеров. Рассмотрено подобие и различие в их пластическом поведении.

Тейтель Е.И., Метлов Л.С., Гундеров Д.В., Корзников А.В. О ПРИРОДЕ ИНДУЦИРУЕМЫХ ИНТЕНСИВНЫМИ ПЛАСТИЧЕСКИМИ ДЕФОРМАЦИЯМИ СТРУКТУРНЫХ И ФАЗОВЫХ ПРЕВРАЩЕНИЙ В ТВЕРДЫХ ТЕЛАХ//Физика металлов и металловедение. 2012. Т. 113. № 12. С. 1230

На основании анализа собственных и литературных данных, а также представлений неравновесной термодинамики рассмотрены особенности влияния больших (интенсивных, мегапластических) пластических деформаций на диффузию, структурные и фазовые превращения в твердых телах при разных температурах. Основные имеющиеся закономерности для всех воздействий можно объяснить с единой точки зрения, основанной на достижении телом критической внутренней энергии за счет высокой плотности накопленных, взаимодействующих и движущихся дефектов. Это приводит к разного рода превращениям вследствие роста энергии фаз до такой степени, что изменяются термодинамика сплавов и фазовые диаграммы, вплоть до перехода сплавов в состояние, термодинамически соответствующее жидкости. Высокая плотность движущихся дефектов облегчает диффузию, что способствует быстрым превращениям даже при температурах жидкого азота.


На основе анализа кинетики дислокаций представлена однопараметрическaя модель, описывающая поведение фрактальной размерности структуры деформируемого твердого тела в широком диапазоне степеней деформации с позиции неравновесной термодинамики. В качестве аргументов в пользу представленной модели приводится её сопоставление с известными и вновь полученными экспериментальными данными

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