Associative polymers, which often exhibit complex rheological and shear-thinning behaviors, have attracted a great deal of interest for applications as diverse as enhanced oil recovery, biomedicine, sensors, and soft robotics.  Despite longstanding interest in the materials and an increasing diversity of accessible chemistries for building associating polymer systems, our knowledge of their mechanics continues to have several gaps.  Our qualitative understanding of these materials is based on transient network theories which to date are primarily tested based on comparisons with rheology.  We have developed a novel rheo-fluorescence instrument that enables measurement of bond breakage during shear, providing an additional data set for the evaluation of these theories.  Comparison of experimental results with predictions shows that theories that include force-induced chain dissociation as the sole method of relaxation are unable to reproduce the very low fraction of dissociated bonds at high shear rates, suggesting a critical role for additional proposed relaxation mechanisms.  Moving beyond bulk mechanical studies, we have also exploited Forced Rayleigh scattering (FRS) as a method for measuring slow diffusive processes in polymer gels, demonstrating super-diffusive behavior that can be reproduced across relatively long length scales by coarse-grained simulation.  However, the short length scale predictions of this theory remain untested.  Here, we extend the performance of the FRS to low length scales and also use neutron spin echo (NSE) in order to provide very low length scale measurements, providing a detailed test for the diffusion theory in associative polymers.

Diffusion and mechanics of associative linear polymers

ACS Spring Meeting 2021

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