Structural glass transition

Material properties can be further classified into fundamental properties and derived properties. Fundamental properties are a direct consequence of the molecular structure, such as van der Waals volume, cohesive energy, and heat capacity. Derived properties are not readily identified with a certain aspect of molecular structure. Glass transition temperature, density, solubility, and bulk modulus would be considered derived properties. The way in which fundamental properties are obtained from a simulation is often readily apparent. The way in which derived properties are computed is often an empirically determined combination of fundamental properties. Such empirical methods can give more erratic results, reliable for one class of compounds but not for another. 

Overview of the Classical Theory of the Structural Glass Transition The Intrinsic Excitations of Amorphous Solids... 

II. OVERVIEW OF THE CLASSICAL THEORY OF THE STRUCTURAL GLASS TRANSITION... 

Monomers Molecular structure Glass transition Order-crystallinity Type of material Solubility Effect of T°... 

The defining property of a structural glass transition is an increase of the structural relaxation time by more than 14 orders in magnitude without the development of any long-range ordered structure.1 Both the static structure and the relaxation behavior of the static structure can be accessed by scattering experiments and they can be calculated from simulations. The collective structure factor of a polymer melt, where one sums over all scattering centers M in the system... 

J. Zinn-Justin, Eds., North-Holland, Amsterdam, 1990, pp. 287-503. Aspects of Structural Glass Transitions. 

It is clear that Tgxp is a function of curing conversion or molecular weight (for linear polymers) at adiff. One can observe a noticeable difference between T xp and T for such processes of polymer synthesis as polyaddition or condensation polymerization reactions. It is especially important for polymers with high T . For many heat-resistant polymers, T is higher than the temperature limit of their chemical decomposition. We can never reach natural T for these polymers. For such polymers, one really measures only Tgxp, the value of which depends on the reaction conditions. For structure-glass transition temperature correlations of networks, T is the most important quantity. 

Permeation and dissolution are the main processes determined by diffusive mass transfer. Permeation of polymers by small molecules depends on their solubility and diffusivity. For both quantities reasonable estimations are possible if some basic data of the permeating molecules (e.g. critical temperature and collision diameter) and of the polymer (structure, glass transition temperature, crystallinity) are known. For the estimation of the permeability of thin layers (films) an additive quantity, the permachor, is available. 

Shalaev, E.Y. Eranks, E. Structural glass transitions and thermophysical processes in amorphous carbohydrates and their supersaturated solutions. J. Chem. Soc. Earaday Trans. 1995, 91, 1511-1517. 

Hayes Method. A relationship between polymer structure, glass transition temperature and molar cohesive energy (cohesive energy density multiplied by the molar volume) was found by Hayes (9) ... 

At Drst Old incoming in dependence (7) expression of experimental models density at their structure glass transition temperatnres. Dependence of cross-linked polymers on temperature is expressed by equation [2]... 

Inductive capacity of unstressed polymer at it is structure glass-transition temperature will determine from equation, derived in [3]... 

TABLE 1 Structural glass transition temperature (Theoretical and experimental values). 

A volume, which elementary links occupy at the structural glass transition temperature, is equated to... 

Experimentally the maximum loss frequency is typically measured for lower temperatures [23, 24] to study the temperature dependence of the structural glass transition or a process. Two sets of experiments in the literature show some discrepancies in an intermediate temperature window but agree with each other and with our simulation data at higher temperatures where we have an overlap temperature window between simulation and experiment. Prom this we can conclude, that also in the experiment one sees no correlations between the dipole moments of different chains. When we furthermore compare the time scale given by the maximum loss frequency with the time scales of the Rouse modes for our chains we can obtain from the simulation, we can say that the dielectric measurements on PB see the relaxation of a chain segment of about 6 backbone carbons, which is exactly the length of a statistical segment of the chains. 

During the last eight years a new theoretical approach to the structural glass transition, the mode coupling theory has been developed... 

Gotze W (1991) Aspects of structural glass transitions. In Hansen J-P, Levesque D, Zinn-Justin J (Eds) Liquids, freezing and glass transition. North-HoUand, Amsterdam, pp 287-504... 

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