Coil to globule transition of homo- and block-copolymer with different topological constraint and chain stiffness

Abstract

In this paper, we present the coil-to-globule (CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The sampling method was a novel enhanced method that efficiently sampled the energy space with low computational costs. The method proved to be efficient and precise to study the structural transitions of polymer chains with complex topological constraint, which may not be easily done by using conventional Monte Carlo method. The topological constraint affects the globule shape of the polymer chain, thus further influencing the CG transition. We found that increasing the topological constraint generally decreased CG transition temperature for homopolymers. For semiflexible chains, an additional first-order like symmetry-broken transition emerged. For block copolymers, the topological constraint did not obviously change the transition temperature, but greatly reduced the energy signal of the CG transition.

Understanding the wettability of a hairy surface: effect of hair rigidity and topology

“…Hairs are chains bonded also by FENE potential with conventional parameters 45 and the harmonic bond angle potential, U b = 1 2 k bend (y À y 0 ) 2 (where k bend is the bending force constant). 47 The rigidity of the hairs is reflected by the harmonic bond angle potential, which can be varied by changing the parameter k bend . A larger k bend force parameter corresponds to more rigid hairs.…”

Two-Step Coil-to-Globule Transition in Mixed Mono-/Polymeric Solvents

“…The coil-to-globule (C–G) transition is the conformational change of a single molecule − and relevant to many interesting phenomena, such as the intrachain crystal nucleation, − gel-network collapse, , interpolymer complexation, − and even DNA or protein packing. − In the monomeric solvent, Lifshitz and co-workers studied the C–G transition based on the assumption that the globule is a uniform spherical droplet with a sharp interface, , and its free energy was obtained by the ground-state dominance. − The transition happens when the interfacial energy is comparable with the volume term in the core, which has a scaling behavior with the chain length as χ t r − 1 / 2 ≈ N 1 − 1 / 2 ( b 3 / v 0 ) 1 / 2 = N 1 − 1 / 2 p 3 / 4 , ,− where p = b 2 / v 0 2/3 is the stiffness parameter ( b is the Kuhn length and v 0 is the monomer volume), and N 1 is the chain length. ,, Recently, a self-consistent field theory (SCFT) was performed to calculate the density profile of the globules, leading to the observation of swollen globule during the C–G transition and a higher solubility limit due to the formation of globules. , …”

Micellization of Diblock Copolymers in Polymeric Solvents

“…In monomeric solvents, the insoluble block of the diblock copolymer in the dilute solution collapses into a compact globule as the temperature decreases, which exhibits the same coil-to-globule (C–G) transition behavior as the homopolymer. − Lu and co-workers found that the topological constraint has a negligible effect on the transition point of the block copolymer. , With the increase in polymer concentration, diblock copolymers can form micelles − and vesicles, where the insoluble block aggregates into a denser core, and the soluble block assembles into a shell to prevent the precipitating. − …”

“…15−19 Lu and co-workers found that the topological constraint has a negligible effect on the transition point of the block copolymer. 20,21 With the increase in polymer concentration, diblock copolymers can form micelles 22−24 and vesicles, 11 where the insoluble block aggregates into a denser core, and the soluble block assembles into a shell to prevent the precipitating. 25−28 The formation of micelles was studied by Ruckenstein and Nagarajan in the framework of dilute solution thermodynamics.…”