On the thermal properties of knotted block copolymer rings

TL;DR

This study explores how knot topology, monomer composition, and temperature affect the structural and thermal properties of knotted diblock copolymer rings using a lattice model and Monte Carlo simulations.

Contribution

It provides new insights into the interplay between topology, composition, and temperature in determining copolymer conformations and thermal behavior.

Findings

Knot topology influences conformational responses over temperature.

Small B-block variations cause nonmonotonic, reentrant behavior.

Transitions between knot localization and delocalization occur at low temperatures.

Abstract

We investigate the thermal and structural properties of knotted diblock copolymer rings using a coarse-grained lattice model in an implicit solvent. The system is studied by means of the Wang--Landau Monte Carlo algorithm, allowing us to analyze thermodynamic and conformational responses over a wide temperature range. Different knot topologies, including the unknot, trefoil, figure-eight, and pentafoil knots, are considered for both symmetric and asymmetric monomer compositions. In the AB model employed here, A-type monomers are self-repulsive, B-type monomers are self-attractive, and A-B interactions are neutral, such that the solvent is effectively good for A-type monomers and poor for B-type monomers at low temperatures. We analyze several key observables, including the heat capacity, the radius of gyration, and its temperature derivative for both the entire copolymer ring and the individual blocks, and the probability that a monomer belongs to the knotted region. Our results show that the interplay between knot topology, monomer composition, and temperature strongly influences polymer conformations. Small variations in the B-block length induce nonmonotonic, reentrant-like conformational behavior as a function of temperature, including transitions between knot localization and delocalization at low temperatures. These effects arise from the competition between energetic and entropic contributions imposed by topological constraints.