Colloidal analogues of charged and uncharged polymer chains with tunable stiffness

TL;DR

This paper introduces versatile methods to create colloidal particle chains with tunable stiffness, enabling detailed observation of polymer-like structures and their properties at the single-particle level.

Contribution

The authors develop a general technique to assemble colloidal chains with controllable stiffness and demonstrate its applicability to various colloidal polymer types.

Findings

Chains can be observed at the single-particle level.

Flexibility of chains can be tuned by ionic strength.

Method is applicable to diverse colloidal polymers.

Abstract

Herein, we describe new methods to produce colloidal particle chains of three stiffness regimes that can be observed on a single-particle level, that is, on the level of the monomers that make up the chain; the chains can even be observed in concentrated systems without using molecular tracers. These methods rely on the following: dipolar interactions induced by external electric fields in combination with long-range charge repulsion to assemble the particles into chains only, and a bonding step to ensure that the particles remain assembled as chains even after the external field is switched off. We can control the length and the flexibility of the chains. Additionally, we demonstrate that our method is generally applicable by using it to prepare several other colloidal polymers, such as block-copolymer chains, which are formed by combining rigid and flexible chains, spherocylinders, which are formed by heating rigid chains, and both atactic and isotactic chains, which are formed from heterodimericparticle monomer units. We demonstrate that the flexibility of the charged chains can be tuned from very rigid (rod-like) to semiflexible (as in the simplified polymer model of beads on a string) by changing the ionic strength. This method can, in principle, be used with any type of colloidal particle. Moreover, our systems can be matched in terms of refractive index and density, so that bulk measurements in real space are possible.