Arrhenius behavior dynamics

Inherent structure analysis of diffusion via molecular dynamics of a deeply supercooled binary Lennard-Jones fluid have provided renewed impetus to the decisive role played by thermodynamic factors [52,53]. The location of the mode crossover temperature and the onset of super-Arrhenius behavior were related to the static structure of the liquid via the potential energy hypersurface [52,53],... 

Abstract For three liquids, salol, propylene carbonate, and o-terphenyl, we show that the relaxation time or the viscosity at the onset of Arrhenius behavior is a material constant. Thus, while the temperature of this transition can be altered by the application of pressure, the time scale of the dynamics retains a characteristic, pressure-independent value. Since the onset of an Arrhenius temperature-dependence and the related Debye relaxation behavior signify the loss of intermolecular constraints on the dynamics, our result indicates that intermolecular cooperativity effects are governed by the time scale for structural relaxation. 

The physical and mechanical properties of materials are the primary concern for their use in applications. However, these properties reflect the motion of the constituent molecules, which makes study of the latter essential to the fundamental understanding necessary for developing new technologies. The structural dynamics is quantified by a time constant, t, which is a measure of the time scale for reorientation of a small molecule or the correlated conformational transitions of a few backbone bonds in a polymer. For both liquids and polymer melts the structural relaxation time (and viscosity, /, which is roughly proportional to t) varies with temperature, with Arrhenius behavior... 

Collet O, Chipot C (2003) Non-arrhenius behavior the unfolding of a short hydrophobic ct-helix. complementarity of molecular dynamics and lattice model simulations. J Am Chem Soc 125 6573-6580. 

In this article, we have discussed two different topics related to the glass transition of thin polymer Aims. As the first topic, we have shown the experimental results of the glass transition and a-dynamics of stacked thin polymer films measured by DSC and DRS. It has been revealed that interfacial interaction can play a crucial role in determining how Tg deviates from the value of the bulk system if the thickness decreases from that of the bulk. Furthermore, annealing above Tg can induce a change in the interfacial interactirMi between thin layers, and this can control the fragility and the non-Arrhenius behavior. 

Figure 9.4. (a) Mean-square atomic fluctuation of protein. This shows a transition around T = 220 K, the mean-square fluctuation becomes low and varies weakly with temperature below T = 220 K. (b) Water dynamics also changes its functional dependence at the same temperature. This is termed dynamic transition. At high temperature the dynamics follows non-Arrhenius behavior (fragile liquid) and at high temperature it follows Arrhenius behavior (strong liquid). Adapted with permission from Proc. Natl. Acad. Sci. USA, 103 (2006), 9012. Copyright (2006) Proc. Natl. Acad. Sci. USA. 

The behavior of methine-labeled poIy(ethyl acrylate)-di (PEA-di), poly(wo-propyl acrylate)-di (PIPA-di), and poly(n-butyl aciylate)-di (PNBA-di) has been studied with deuterium NMR relaxation time measurements in concentrated solutions with chloroform. PEA-di and PNBA-di behaved similarly in terms of solution dynamics, but PIPA-di was found to reorient significantly faster at similar concentrations. The relaxation times were fitted to a log-normal distribution of correlation times and the resulting mean correlation times fit to Arrhenius behavior. The energies of activation were found to increase with increasing concentration from about 6 kJ/mol at lower concentrations to 10-20 kJ/mol from about 40 to 80 wt % polymer. 

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