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

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.