2026 Student Poster Award - 2nd Place

Shear-induced nematic alignment in polysulfone melts

Sara Daryoush | Pennsylvania State University
Tiago outerelo corvo | Pennsylvania State University
Enrique Gomez | Pennsylvania State University
Ralph Colby | Pennsylvania State University

Abstract

Polymer melt processing commonley imposes tempereture and shear condition thet give rise to flow-induced structures, which profoundly affect the properties of the resulting materials. Such effect is connected to chain stretching, often leading to shear-induced nematic alignment of at least the longest chains, reported for rod-like polymers but also polyolefins. The chain stiffness of a polysulfone melt is numerically determined from the tangeant correlation decay along a freely rotating chain model. Its moderate chain stiffness and linearity, supported by the strong agreement between the linear viscoelastic data and the branch-on-branch (BoB) tube model, together with its amorphous nature, make polysulfone a suitable system for investigating the temperature dependence of nematic alignment. Such behavior is monitored by both rheology, exhibiting a failure of the Cox-Merz rule, and birefringence by means of an in situ reflection polariscope. The critical shear rate for the onset of nematic alignment is determined over a range of temperatures and compared with the prediction based on the Rouse relaxation time of the longest chains, commonly regarded as the controlling timescale. Although the onset shear rate for nematic alignment share the same temperature dependence as the chain relaxation times, suggesting chain stretching is the underlying mechanism, the critical shear rate is much smaller than expected. The origin of this discrepancy in polysulfone behavior is discussed in relation to possible π–π stacking interactions that may help stabilize the nematic domains.

2^nd Place, 97^th Annual Meeting, Oct 2026, Boston