TIT# Short-term morphology relaxation of three elastomers after fast 
     strain steps
AUT# Stribeck, Almut; Schneider, Konrad; Eling, Berend; Pöselt, Elmar;
SOU# Macromol. Mater. Eng. (2020), 305(9), 2000386
DOI# 10.1002/mame.202000386
LOC# xv164
CLA#
COM# Title story (issue: September 2020)
APP#
MAT#
ABS# Strain steps are subjected to elastomers in a pneumatic relaxometer and
     monitored by small-angle X-ray scattering (SAXS). The relaxometer 
     provides a rise time of 13 ms for strain pulses of step height 
     Δε=±1 in strain. The basic character of the two-dimensional SAXS frames is
     examined and corresponding invariants Q(t) are analyzed. 3 Thermoplastic
     polyurethanes (TPU) of hardness 85 Shore A with different soft segments
     are studied both unannealed and annealed. The first response of all
     materials is a fast morphology conversion which finishes within 
     $t_{mc}$=250 ms. Because it has been untraceable, it is characterized by
     a settling lift Q(t_{mc})-Q(0). The second response is a slow morphology
     adjustment process which complies with logarithmic relaxation. It is
     characterized by a relaxation rate D_{Q}=Q(10 t)/Q(t)-1. Comparison 
     indicates that the nanoscopic morphology relaxation processes appear to
     have little direct relation to the macroscopic stress relaxation curves.
     The materials differ with respect to hard-domain morphology stability and
     morphology recovery. Most unstable is the morphology of the annealed 
     polyether-based material. It forms nanofibrillary entities when strained.