Glass transition theory kinetic theories

Craig, I.D., Parker, R., Rigby, N.M., Cairns, P., and Ring, S.G. 2001. Maillard reaction kinetics in model preservation systems in the vicinity of the glass transition Experiment and theory. J. Agric. 

Craig ID, Parker R, Rigby NM, Cairns P, Ring SG. MaiUard reaction kinetics in model preservation systems in the vicinity ofthe glass transition experiment and theory, f Agric Food Chem 2001 49(10) 4706-4712. 

The thermodynamic theories [7,8] deny the pure kinetic nature of the glass transition and link it directly to thermodynamic quantities like the configurational entropy of the material. Some recent results suggest a correlation between kinetic quantities and thermodynamic parameters [9]. Also recently, this theory was successfully merged with a potential landscape approach [10]. The thermodynamic approach is interesting since it reflects the different configurations that are allowed not only for the whole ensemble but also for the internal conformations... 

A unified approach to the glass transition, viscoelastic response and yield behavior of crosslinking systems is presented by extending our statistical mechanical theory of physical aging. We have (1) explained the transition of a WLF dependence to an Arrhenius temperature dependence of the relaxation time in the vicinity of Tg, (2) derived the empirical Nielson equation for Tg, and (3) determined the Chasset and Thirion exponent (m) as a function of cross-link density instead of as a constant reported by others. In addition, the effect of crosslinks on yield stress is analyzed and compared with other kinetic effects — physical aging and strain rate. 

William Russel May I follow up on that and sharpen the issue a bit In the complex fluids that we have talked about, three types of nonequilibrium phenomena are important. First, phase transitions may have dynamics on the time scale of the process, as mentioned by Matt Tirrell. Second, a fluid may be at equilibrium at rest but is displaced from equilibrium by flow, which is the origin of non-Newtonian behavior in polymeric and colloidal fluids. And third, the resting state itself may be far from equilibrium, as for a glass or a gel. At present, computer simulations can address all three, but only partially. Statistical mechanical or kinetic theories have something to say about the first two, but the dynamics and the structure and transport properties of the nonequilibrium states remain poorly understood, except for the polymeric fluids. 

This more sophisticated way shows a [arge distribution of residence times for water molecules in the cage formed by the neighboring molecules, which is a more realistic view than the sharp separation of water molecules into two classes, according to their mobility [49]. Short time dynamics resuits about hydrated myoglobin have recently been interpreted by using this same theory of kinetic glass transition in dense supercooled liquids [73]. 

If La " acts merely to increase the glass transition temperature, as a result of copolymerization then the "rubbery modulus of the material should not necessarily change if, on the other hand, it does crosslink the material, then the rubbery modidus should change in a manner predicted by the kinetic theory. 

Although glass transition is conventionally defined by the thermodynamics and kinetic properties of the structural a-relaxation, a fundamental role is played by its precursor, the Johari-Goldstein (JG) secondary relaxation. The JG relaxation time, xjg, like the dispersion of the a-relaxation, is invariant to changes in the temperature and pressure combinations while keeping xa constant in the equilibrium liquid state of a glass-former. For any fixed xa, the ratio, T/G/Ta, is exclusively determined by the dispersion of the a-relaxation or by the fractional exponent, 1 — n, of the Kohlrausch function that fits the dispersion. There is remarkable similarity in properties between the JG relaxation time and the a-relaxation time. Conventional theories and models of glass transition do not account for these nontrivial connections between the JG relaxation and the a-relaxation. For completeness, these theories and models have to be extended to address the JG relaxation and its remarkable properties. 

Major open questions where landscape-based ideas should prove helpful include the possible thermodynamic basis for the glass transition (Debenedetti et al., 1999), the relationship between kinetics and thermodynamics of deeply supercooled liquids and glasses (Adam and Gibbs, 1965 Wolynes, 1988), and translation-rotation decoupling and the breakdown of the Stokes-Einstein relationship in supercooled liquids (Fujara et al., 1992). In addition, the reformulation of the thermodynamics of hquids embodied in Eqs. (16), (52), (55), (56), (61), and (62) suggests that understanding basic topological features of a landscape s density-dependent statistics could lead to improved theories of simple and complex liquids. As explained in Section V, landscape statistics can be obtained from experiments, theory, and simulations. 

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