Cooperativity and materials' - New insights and quantitative predictions


This research is leading to a detailed model of materials dynamics that accounts for its cooperative nature. The main results so far are the (1) prediction of individual process and average frequencies within materials' structure; (2) prediction of their relative weight (materials frequency, or characteristic time, spectrum), including a quantitative measure of the changes in the effective cooperativity with temperature and the time scale of the experiment as measured by the sizes of active clusters of relevant elements of the structure; (3) prediction of time-, temperature- and excitation-dependent responses in e.g. mechanical creep that naturally turn out consistent with KWW dynamics and time-temperature superposition at not too low temperatures - VTF or WLF at low to moderate temperatures (within a range narrower than 100 K), to Arrhenius at high temperatures - as experimentally observed; (4) prediction of dynamic (temperature scanning rate- or excitation frequency-dependent) responses to thermal and e.g. mechanical excitations and (5) a proposition for the microscopic clarification of the origin of the crossover region. The temperature-dependent average characteristic time (or frequency) of the structure gradually turns out super-Arrhenius at low temperature. The theory may be extrapolated to any fast or slow time: scales, with no additional computational burden, and explicitly includes the equilibrium (infinite time scale) thermodynamic behavior.




Science & Technology - Other Topics; Mechanics; Physics; Polymer Science


Joaquim, J; Pinto, CC


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