Dynamic viscoelastic relaxations of nematic solutions of poly(p-phenylene terephthamide) in sulfuric acid after cessation of shearing

摘要

This rheological study investigated strain recovery and evolution of dynamic moduli (G '') of nematic poly(p-phenylene terephthamide)/H2SO4 solutions after cessation of shearing. Recoil experiment showed a large recoverable strain when the prestrain was smaller than 20 strain units. When the prestrain was larger than 50 strain units, the relative recoverable strain turned out to be small. After cessation of steady-state shearing, the variation of G '' with time was determined by the preshear rate ((gamma) over dot(p)). When (gamma) over dot(p) was low in Region I of the flow curve, G '' slowly increased with time after cessation of shearing. On the contrary, when (gamma) over dot(p) was high in Region III, G '' quickly decreased with the time. In a wide range, G '' first increased and then decreased with the time of relaxation. After cessation of the steady-state shearing, scaling relationships of the time and (gamma) over dot(p) were observed for both G '' increasing and decreasing stages as well as the first stage of the strain recovery. (C) 2015 Elsevier Ltd. All rights reserved.