Phenomenological treatment of dynamic glass transition heterogeneity

Relaxation in Poly(alkyl methacrylate)s: Crossover Region and Nanophase Separation

“…The a process above the crossover (T A T on ) is interpreted as a more localized cage-escape motion as discussed in the literature. [88,107] No dynamic heterogeneity is expected in this temperature range. It is assumed that no intermolecular cooperativity is required above T on for a single particle to escape the cage formed (randomly) by its nearest neighbors.…”

“…An empirical picture for the relaxation processes above and below T on is suggested in the literature. [88,93,107] The idea is that intermolecular cooperativity starts at the onset temperature T on in the crossover region, i. e., dynamic heterogeneity and CRRs are assumed to exist only below T on . With decreasing temperature the a motions involve a larger and larger number of particles N a in a cooperative way.…”

“…Probably the situation is more complex in this case or other crossover scenarios exist. [25,61,107] Free Volume Concept Differences in free volume [111,112] are a way to explain changes in T g or the frequency temperature position of the a relaxation in glasses. An increase in free volume is connected with a decrease in glass temperature.…”

Fluctuation approach for the estimation of the dynamic heterogeneity in glass-forming liquids from the dispersion in o-Ps lifetimes: Free volume fluctuations in polymers

“…(6) are mean values representative for the bulk properties. Then hV SV i can be considered as volume of the smallest representative freely fluctuating subsystem related to structural relaxation (compare gedankenexperiment by Donth [14]). This volume has a similar meaning as volume of a cooperatively rearranging region (CRR) of the Adam-Gibbs theory [11] which mirrors the dynamic heterogeneity of the glass transition [2,14].…”

“…Values for n of 1-3 nm 3 at glass transition were estimated [4] and confirmed by nuclear magnetic resonance experiments [12], for example. Another fluctuation formula which considers temperature fluctuations has been derived by Donth [2,[13][14][15][16][17][18][19]. Results of this approach will be discussed later.…”