Giant Casimir non-equilibrium forces drive coil to globule transition in polymers

TL;DR

This paper develops a theory predicting that non-equilibrium Giant Casimir Forces can induce a coil-to-globule transition in polymers under a temperature gradient, with potential experimental verification.

Contribution

It introduces a novel theoretical framework linking non-equilibrium fluctuation-induced forces to polymer conformational transitions.

Findings

GCF causes attractive interactions between monomers in non-equilibrium conditions.

A critical temperature gradient scales with polymer length as N^{-5/4}.

Predictions are testable via light-scattering experiments.

Abstract

We develop a theory to probe the effect of non-equilibrium fluctuation-induced forces on the size of a polymer confined between two horizontal thermally conductive plates subject to a constant temperature gradient, $\nabla T$. We assume that (a) the solvent is good and (b) the distance between the plates is large so that in the absence of a thermal gradient the polymer is a coil whose size scales with the number of monomers as $N^{\nu}$, with $\nu \approx 0.6$. We predict that above a critical temperature gradient, $\nabla T_c \sim N^{-\frac{5}{4}}$, favorable attractive monomer-monomer interaction due to Giant Casimir Force (GCF) overcomes the chain conformational entropy, resulting in a coil-globule transition. The long-ranged GCF-induced interactions between monomers, arising from thermal fluctuations in non-equilibrium steady state, depend on the thermodynamic properties of the fluid. Our predictions can be verified using light-scattering experiments with polymers, such as polystyrene or polyisoprene in organic solvents (neopentane) in which GCF is attractive.