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Meeting ID: 871 2853 4826 (Password: rheology)

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Seminar Speakers

Alex Rispo Constantinou | University of Naples Federico II + Université catholique de Louvain

Entropic phase separation in polymer–vitrimer melts

Abstract:
Vitrimeric polymers have recently been proposed as a reprocessable alternative to thermoset plastics. Their potential recyclability stems from the dynamic covalent bonds forming the polymeric network: vitrimers are solid-like at low temperatures, but flow when heated. One application involves adding them to a classical thermoplastic to cheaply improve its thermomechanical properties whilst maintaining reprocessability. An obstacle to the production of homogeneous vitrimeric plastics, however, is the onset of phase separation during synthesis. We investigate this phenomenon, adapting existing theories for dissociative polymeric networks to the associative case of vitrimers in a polymeric matrix.

We find that entropic effects suffice to incite separation into different phases, even in the absence of energetic interactions between species. These results are backed by comparison to Monte-Carlo molecular-dynamics simulations. We thus provide a simple theoretical approach to predicting phase separation in polymer–vitrimer melts, meant to guide experimental exploration of such materials’ design space and facilitate their industrial production.

Surendra Padamata | Penn State University

Symmetry and Memory in Non-Brownian Suspensions

Abstract
Steadily shearing a non-Brownian suspension forms a memory of direction in its structure, while
periodically shearing it forms a memory of amplitude. Our experiments show that these memories coexist and compete within a limited memory capacity. A specific oscillatory amplitude, previously associated with a critical transition, suppresses the directional (fore-aft) asymmetry. A similar picture is known in amorphous solids. We propose that these competing kinds of memory are a motif for non-equilibrium systems coupled to a uniaxial drive, and are a basic example of interplay
between memories.