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| - A DSC Study of α- and β-Relaxations in a PS−Clay System
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| - Differential scanning calorimetry has been used to study the α-relaxation (glass transition) as well asβ-relaxation (sub-Tg relaxation) in both virgin polystyrene (PS) and PS−clay nanocomposite. The β-relaxationshave been measured as a small endothermic peak that appears on heating of the samples previously annealedat temperatures from 30 to 80 °C. The relaxations have been characterized by determining the effectiveactivation energies (E) and evaluating the sizes of cooperatively rearranging regions at the glass transition(Vg). The values of Vg have been determined from the heat capacity data. The β-relaxation in both systemsshows comparable values of E that increase with annealing temperature from ∼90 to 170 kJ mol-1. In thePS−clay system the increase occurs slower, suggesting that this process is more decoupled from the α-relaxationthan in virgin PS. The α-relaxation demonstrates markedly larger values of E (∼340 vs ∼270 kJ mol-1) forthe PS−clay system than for virgin PS. The PS−clay system has also been found to have a significantlylarger value of Vg, 36.7 nm3 as compared to 20.9 nm3 for PS. The increase in E and Vg reflects an increasein molecular cooperativity that is introduced by the mutually dependent motion of the polymer chains anchoredto the surface of clay sheets.
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