The nature and determination of the dynamic glass transition temperature in polymeric liquids (original) (raw)
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The Journal of Chemical Physics, 2005
Characteristic temperatures and structural relaxation times for different classes of glass-forming polymer liquids are computed using a revised entropy theory of glass formation that permits the chain backbone and the side groups to have different rigidities. The theory is applied to glass formation at constant pressure or constant temperature. Our calculations provide new insights into physical factors influencing the breadth of the glass transition and the associated growth of relaxation times.
Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle
Polymer, 2007
A semi-empirical method based on the mass-per-flexible-bond (M/f ) principle was used to quantitatively explain the large range of glass transition temperatures (T g ) observed in a library of 132 L-tyrosine derived homo, co-and terpolymers containing different functional groups. Polymer class specific behavior was observed in T g vs. M/f plots, and explained in terms of different densities, steric hindrances and intermolecular interactions of chemically distinct polymers. The method was found to be useful in the prediction of polymer T g . The predictive accuracy was found to range from 6.4 to 3.7 K, depending on polymer class. This level of accuracy compares favorably with (more complicated) methods used in the literature. The proposed method can also be used for structure prediction of polymers to match a target T g value, by keeping the thermal behavior of a terpolymer constant while independently choosing its chemistry. Both applications of the method are likely to have broad applications in polymer and (bio)material science.
The Glass Transition Temperature of Polymer Melts †
The Journal of Physical Chemistry B, 2005
We develop an analytic theory to estimate the glass transition temperature T g of polymer melts as a function of the relative rigidities of the chain backbone and side groups, the monomer structure, pressure, and polymer mass. Our computations are based on an extension of the semiempirical Lindemann criterion of melting to locate T g and on the use of the advanced mean field lattice cluster theory (LCT) for treating the themodynamics of systems containing structured monomer, semiflexible polymer chains. The Lindemann criterion is translated into a condition for T g by expressing this relation in terms of the specific volume, and this free volume condition is used to calculate T g from our thermodynamic theory. The mass dependence of T g is compared to that of other characteristic temperatures of glass-formation. These additional characteristic temperatures are determined from the temperature variation of the LCT configurational entropy, in conjunction with the Adam-Gibbs model for long wavelength structural relaxation. Our theory explains generally observed trends in the variation of T g with polymer microstructure, and we find that T g can be tuned either upward or downward by increasing the length of the side chains, depending on the relative rigidities of the side groups and the chain backbone. The elucidation of the molecular origins of T g in polymer liquids should be useful in designing and processing new synthetic materials and for understanding the dynamics and controlling the preservation of biological substances.
Temperature Dependence of Structural Relaxation in Glass-Forming Liquids and Polymers
Entropy
Understanding the microscopic mechanism of the transition of glass remains one of the most challenging topics in Condensed Matter Physics. What controls the sharp slowing down of molecular motion upon approaching the glass transition temperature Tg, whether there is an underlying thermodynamic transition at some finite temperature below Tg, what the role of cooperativity and heterogeneity are, and many other questions continue to be topics of active discussions. This review focuses on the mechanisms that control the steepness of the temperature dependence of structural relaxation (fragility) in glass-forming liquids. We present a brief overview of the basic theoretical models and their experimental tests, analyzing their predictions for fragility and emphasizing the successes and failures of the models. Special attention is focused on the connection of fast dynamics on picosecond time scales to the behavior of structural relaxation on much longer time scales. A separate section disc...
Quantitative relationships between structure and glass transition temperature T g and of polyethylene analogues has been studied. The study was done by using molecular modeling of polymer assumed in trimeric compound in their indiotactic form and the calculation was performed by semiempirical AM1 method. The physicochemical properties of molecule was focused on 11 descriptors i.e. atomic net charges of carbon atom as the head and tail of the polymer chain (qC 1 and qC 2 ), polarizability (α), moment dipole (μ), refractivity index, partition coefficient of n-octanol-water (log P), molecular weight (MW), volume van der Waals (V VDW ), molecular surface area, Parachor index and solubility in the water (log SW). Correlation analysis of T g polymers to those predictors was based on statistical technique of multiple linear regression. The QSPR model resulted is relatively good in terms of accuracy of calculate T g values of polymer. However the QSPR model is still limited by the validity of the experimental data that were used to derive the regression coefficients of the QSPR equation.
Methods of Polymers Analysis, 2020
In this research, some thermo-physical (glass transition temperature, Tg; melting point, Tm) and mechanical properties (tensile strength, TS; Young’s modulus, Y) of hydrophobic polymers were studied. The linear dependences between these properties and the specific cohesive energy were obtained. It was found that the studied properties of polymer materials correlate much better with the volume cohesive energy (Ev) than with the molar cohesive energy. The linear regression equations, Z = k Ev + C, with high correlation coefficients were calculated, where Z is property, k and C are coefficients. The dependences of various properties of polymers on Tg were also studied. It was shown that the obtained relationships allow to predict some properties of polymer materials with a sufficiently good reliability.
Glass Transition Temperatures of Polymers from Molecular Dynamics Simulations
Macromolecules, 1994
Progress has been made recently in using molecular dynamics (MD) simulations to generate PVT properties of amorphous polymers. In the present work previous MD simulations of V-T curves for several polymers are extended to lower temperatures, including through the glass transition. It is demonstrated that these V-T curves can be used to locate volumetric glass transition temperatures (T,) reliably. Four polymers, namely, cis-poly(1,3-butadiene), polyisobutylene, atactic polypropylene, and polystyrene were studied, and previously determined MD data for polyethylene (PE) are available. The Tg values span a range of 200 K, from 170 to 370 K. The values from .the MD V-T curves tend to be displaced, as expected, to somewhat higher temperature than the longer time experimental values. However, the displacements are minor compared to the range of Tg values considered. Determination of Tg from MD simulations appears to be a practical procedure. The relation of the MD-determined Tg of wholly amorphous PE to experimental values in the semicrystalline environment is discussed.
MRS Proceedings, 1995
Results from the NIST torsional dilatometer have indicated that after a temperature step from equilibrium, the volume (structure) and mechanical response (physical aging) can evolve at different rates, depending on the temperature history. The torsional dilatometer results have been modeled in two ways. First, it was assumed that the volume and mechanical response are governed by different clocks, with the principle of time-aging time superposition employed to evaluate an aging time shift factor ak from the torsional response, which was then compared to a structural shift factor a, calculated from the evolution of the volume. These results were also investigated using a thermoviscoelastic model based on rational thermodynamics and configurational entropy; this model does not include an explicit assumption of separate time scales, but different time scales for the structure and mechanical properties appear to arise naturally from the formulation. The results from the thermoviscoelastic model show good qualitative agreement with the torsional dilatometer results, although more material data is needed to make an exact comparison.