Cellulose-derived Nanoparticle Stabilized Pickering Emulsions: Connecting Rheology to Droplet Clustering via Confocal Imaging

Sustainable Pickering emulsions are stabilized by environmentally friendly emulsifiers instead of traditional surfactants. We characterize a model iso-refractive Pickering emulsion system stabilized by biodegradable cellulose acetate nanoparticles (NP) comprising mineral oil droplets dispersed in glycerol. By combining rheology with real-time microscopic visualization, we draw parallels between bulk rheological parameters and emulsion droplet size and microstructure. Microstructure breakdown videos show that emulsion droplets form attractive clusters with varying interaction strengths depending on the NP concentrations. In the linear regime these clusters form stable gel networks which maintain their stability up to the cross-over strain beyond which they disintegrate, with droplets undergoing coalescence and rupture. Droplet and cluster stability increases with NP concentration despite the clusters yielding at lower strains at higher NP concentrations. Additionally, large amplitude oscillatory strain (LAOS) analysis correlates intracycle strain hardening to droplet deformation, assessed through particle tracking. This study provides insights into the breakdown of polydisperse Pickering emulsions by correlating image analysis with rheological characterization.