# Diffusiophoretic manipulation of particles in a drop deposited on a hydrogel

## TL;DR

This study demonstrates how diffusiophoresis can be used to control colloidal particle movement in drops on hydrogels, enabling targeted particle deposition through solute gradient manipulation.

## Contribution

It introduces an experimental approach to manipulate particles in hydrogel drops using diffusiophoresis, supported by a numerical model.

## Key findings

- Particles move toward or away from the interface depending on solute gradient and charge.
- Diffusiophoresis significantly influences particle motion at the drop scale.
- Method enables controlled particle deposition on hydrogels.

## Abstract

We report an experimental study on the manipulation of colloidal particles in a drop sitting on a hydrogel. The manipulation is achieved by diffusiophoresis, which describes a directed motion of particles induced by solute gradients. By letting the solute concentrations for the drop and the hydrogel be different, we control the motion of particles in a stable suspension, which is otherwise difficult to achieve. We show that diffusiophoresis can cause the particles to move either toward or away from the liquid-air interface depending on the direction of the solute gradient and the surface charge of the particles. We measure the particle adsorption experimentally and rationalize the results with a one-dimensional numerical model. We show that diffusiophoretic motion is significant at the lengthscale of a drop deposited on a hydrogel, which suggests a simple method for the deposition of particles on hydrogels.