Physics of thick polymers

TL;DR

This paper investigates the behavior of thick polymers, revealing a new phase transition influenced by thickness, with implications for understanding protein structures and polymer phases through analytic and numerical methods.

Contribution

Introduces a novel model of thick polymers using a three-body interaction, uncovering new phase transitions and structural formations relevant to proteins and polymers.

Findings

Discovery of a phase transition between compact and swollen phases at zero temperature.

Formation of space-filling helices and sheets near the transition, similar to protein structures.

Observation of a crossover from secondary structures to semi-crystalline or amyloid-like phases with increasing chain length.

Abstract

We present the results of analytic calculations and numerical simulations of the behaviour of a new class of chain molecules which we call thick polymers. The concept of the thickness of such a polymer, viewed as a tube, is encapsulated by a special three body interaction and impacts on the behaviour both locally and non-locally. When thick polymers undergo compaction due to an attractive self-interaction, we find a new type of phase transition between a compact phase and a swollen phase at zero temperature on increasing the thickness. In the vicinity of this transition, short tubes form space filling helices and sheets as observed in protein native state structures. Upon increasing the chain length, or the number of chains, we numerically find a crossover from secondary structure motifs to a quite distinct class of structures akin to the semi-crystalline phase of polymers or amyloid fibers in polypeptides.