# Photo-Triggered Charge Control Induces Dissociation of Complex Coacervates

## TL;DR

This paper shows how light can be used to control the formation and breakdown of coacervate droplets made from charged polymers.

## Contribution

The novel contribution is the development of a light-responsive polyampholyte that allows for photo-triggered dissociation of coacervates.

## Key findings

- A photo-responsive polyampholyte was synthesized with controllable charge states via light exposure.
- Light-induced charge changes in the polyampholyte led to the dissociation of coacervates formed with an anionic polyelectrolyte.
- The study provides a design strategy for light-controlled electrostatic interactions in polymeric systems.

## Abstract

In this study, we designed a statistical polyampholyte bearing cationic quaternary ammonium salts and anionic phosphate groups as pendant functionalities. In addition, small amounts of o-nitrobenzyl groups, which generate anionic species upon photoirradiation, were introduced into the pendant chains to prepare a photo-responsive polyampholyte via reversible addition-fragmentation chain transfer radical polymerization. By increasing the feed ratio of the cationic monomer during copolymerization, a polyampholyte with a net positive charge was obtained. Upon photoirradiation of the aqueous solution of this cationic polyampholyte, the fraction of negatively charged groups in the polymer increased, resulting in a decrease in the zeta potential from positive values to around 0 mV. When the photo-responsive cationic polyampholyte was mixed with an anionic polyelectrolyte, poly(2-acrylamido-2-methylpropanesulfonate) (PAMPS), in water, micrometer-sized coacervate droplets were formed via electrostatic interactions. Photoirradiation of the aqueous coacervate system increased the fraction of negative charges in the polyampholyte, thereby weakening the electrostatic interactions with anionic PAMPS and resulting in the dissociation of the coacervates. Overall, this study presents a design guideline for polymeric materials in which interpolymer electrostatic interactions can be controlled by light to induce the disappearance of coacervates.