# Linking Viscosity and Droplet Microstructure in Liquid Metal Composites via 3D MicroCT Analysis

## TL;DR

This study uses 3D imaging to show how the viscosity of liquid metal composites affects their microstructure, which is important for making better soft electronics and robotics.

## Contribution

The novel integration of rheology and 3D microCT imaging reveals how composite viscosity controls droplet microstructure in liquid metal composites.

## Key findings

- MicroCT analysis shows that LM volume and fumed silica content influence droplet size and dispersion.
- Rheological properties determine microstructural homogeneity and electrical conductivity upon indentation.
- A 105x increase in electrical conductivity is achievable by tailoring composite microstructure.

## Abstract

Liquid metal (LM) composites offer unique combinations of compliance, conductivity, and functionality that enable applications in soft robotics, wearable devices, and flexible electronics. Realizing these capabilities requires a fundamental understanding of how processing influences microstructure, since droplet size, dispersion, and settling govern material properties. Here, rheological measurements are combined with micro‐computed tomography (microCT) imaging to uncover how uncured composite viscosity directs the formation of LM microstructures in elastomeric matrices. By systematically varying LM volume fraction (ϕ = 10%, 20%, 30%) and fumed silica (FS) weight fraction (ψ = 0%, 4%, 8%) while holding planetary mixing conditions constant, the role of rheology is isolated in shaping LM droplet populations. MicroCT analysis provides quantitative 3D characterization of thousands of droplets, enabling statistical evaluation of size distributions, spatial dispersion, and settling behavior. These findings are further analyzed by modeling LM droplet settling during polymer curing, enabling the prediction of microstructural homogeneity and providing a design tool for tailoring composite properties. This approach reveals how composite rheology dictates LM microstructure, which can be modified to achieve a ≈ 105x increase in electrical conductivity upon indentation. These insights provide design guidelines for processing LM composites with tailored microstructures, advancing their performance in functional devices.

This work connects rheology and microstructure in liquid metal composites through 3D microCT imaging. Quantitative analysis of thousands of droplets reveals how liquid metal and fumed silica contents dictate droplet size, settling, and dispersion, providing design principles for processing‐structure control and advancing high‐performance, multifunctional soft composites.