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Current Trends in Polymer Science   Volumes    Volume 13 
Relaxations of rubbing induced birefringence in glassy polymers
Z. Yang
Pages: 69 - 99
Number of pages: 31
Current Trends in Polymer Science
Volume 13 

Copyright © 2009 Research Trends. All rights reserved

Using a simple process of rubbing with a velvet cloth on a glassy polymer surface at room temperature, we place the polymer in a non-equilibrium form that has never been attained before. In rubbed polymers the segments are distorted, in addition to being aligned by the rubbing process. The relaxations of rubbing induced birefringence (RIB) in several glass forming polymers, including polycarbonate, polystyrene (PS), and PS derivatives with various modifications to the phenyl ring side group, are studied. Significant relaxations of RIB, with relaxation times spanning a wide range from ~ 10 s to probably geological time scale, are observed at temperatures tens of degrees below the glassy temperature Tg. Physical aging effects are absent in the RIB relaxations. A phenomenological model is proposed and shown to describe well the RIB relaxations in all the polymers investigated so far. The energy barriers found from the analysis within the framework of the model are of the order of a few hundred kJ/mol and decrease with decreasing temperature, in opposite of the trend of Vogel – Tammann – Fulcher form for polymer segmental relaxations above Tg. The relaxation behaviors of different polymers are qualitatively similar but somewhat different in quantitative details, such as in the values of the saturated birefringence, the shape of the initial barrier density distribution functions, the rates of barrier decrease with decreasing temperature, and the dependence of relaxation times on temperature and individual barrier height parameter ξ, etc. The RIB relaxations are different from any of the other relaxations below Tg that have been reported so far in the literature, such as dielectric relaxations or optical probe relaxations. A first-principle microscopic model for the relaxations of RIB, however, is still lacking. Buy this Article


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