# Refractive Index Matched Scanning and Detection of Soft Particle

## TL;DR

This paper presents a method combining refractive index matched scanning and numerical analysis to image and analyze deformed hydrogel spheres in 3D, enabling stress measurement in soft particle packings.

## Contribution

It introduces a specialized imaging and detection approach for hydrogel spheres, including handling techniques and numerical methods for identifying deformed, contacting particles.

## Key findings

- Successful 3D imaging of hydrogel spheres using index matching.
- Numerical techniques for detecting non-spherical, contacting particles.
- Experimental access to stress tensors in soft particle packings.

## Abstract

We describe here how to apply the three dimensional imaging technique of refrecative index matched scanning to hydrogel spheres. Hydrogels are water based materials with a low refractive index, which allows for index matching with water-based solvent mixtures. We discuss here various experimental techniques required to handle specifically hydrogel spheres as opposed to other transparent materials. The deformability of hydrogel spheres makes their identification in three dimensional images non-trivial. We will also discuss numerical techniques that can be used in general to detect contacting, non-spherical particles in a three dimensional image. The experimental and numerical techniques presented here give experimental access to the stress tensor of a packing of deformed particles.