Revealing polymerization kinetics with colloidal dipatch particles

TL;DR

This study explores the dynamics of 2D polymerization of colloidal particles bonded by critical Casimir forces, revealing how concentration and valency influence growth, diffusion, and phase transitions, with implications for synthetic and biological polymers.

Contribution

It provides direct observation of 2D polymerization dynamics with tunable interactions, highlighting the effects of valency and concentration on growth and phase behavior.

Findings

Dilute polymers follow exponential size distributions consistent with Flory theory.

Concentrated samples exhibit arrested diffusion due to isotropic-nematic transition.

Adding higher-valency particles creates networks, altering growth dynamics.

Abstract

Limited-valency colloidal particles can self-assemble into polymeric structures analogous to molecules. While their structural equilibrium properties have attracted wide attention, insight into their dynamics has proven challenging. Here, we investigate the polymerization dynamics of semiflexible polymers in two dimensions (2D) by direct observation of assembling divalent particles, bonded by critical Casimir forces. The reversible critical Casimir force creates living polymerization conditions with tunable chain dissociation, association and bending rigidity. We find that unlike dilute polymers that show exponential size distributions in excellent agreement with Flory theory, concentrated samples exhibit arrest of rotational and translational diffusion due to a continuous isotropic-to-nematic transition in 2D, slowing down the growth kinetics. These effects are circumvented by addition of higher-valency particles, cross-linking the polymers into networks. Our results connecting polymer flexibility, polymer interactions and the peculiar isotropic-nematic transition in 2D offer insight into polymerization processes of synthetic two-dimensional polymers, and biopolymers at membranes and interfaces.