Do chain topology and polydispersity affect the two-stage heteropolymer coil-globule transition?

Abstract

The thermodynamic behavior of collapse transition in a fully flexible coarse-grained model of energy polydisperse polymer (EPP), a statistical model of random heteropolymer, is investigated in an implicit solvent by means of molecular dynamics (MD) simulations. Each monomer has interaction energy, $\varepsilon_i$, randomly drawn from a Gaussian distribution, and is characterised by polydispersity index, $\delta$ = standard deviation/mean, where the mean is fixed at $\langle \varepsilon \rangle$ = 2.5. Polymers of different chain topologies assume an expanded coil conformation at high temperature, and undergo a melting transition called a coil-globule transition when temperature is lowered. They collapse into molten globules. Further decrease in temperature results in a liquid-solid transition called a freezing transition, thus, creating crystallite structures at very low temperatures. The current study investigates the effect of chain topology and energy polydispersity in this regard from thermodynamic point of view.