Insights into the thermal responsiveness of W/O emulsions with nanoparticles and oleogels as building blocks

Abstract

Understanding the thermal behavior of emulsions with complex structures was crucial for wider applications. However, the correlations between the structural units and emulsion properties at different temperatures are poorly understood. Herein, W/O emulsions stabilized by oleogels and nanoparticles were studied during thermal process, and dynamic interactions among the structural units occurred at micro-, meso-, and macroscales. Results revealed that the thermal behavior of W/O emulsions shifted from stable (25–50 °C) to sub-stable (50–60 °C), and unstable states (60–80 °C). Microstructural analysis confirmed that the particles desorbed from the interface and dissolved in the oil phase after heating, causing water droplet coalescence in the emulsions. This was attributed to the enhanced hydrophobic interactions between the particle dispersions and the oleogel, as the contact angle and interfacial tension were decreased during heating. At the mesoscale, the T2 values of oleogels and nanoparticle dispersion were increased more than three times from 25 °C to 80 °C, leading to the higher mobility of protons in emulsions. At the macroscale, the viscoelastic modulus of emulsions at higher temperature were higher, together with less energy dissipated by friction and increased nonlinear response. Furthermore, the temperature-induced transformation of emulsion stability can be reversibly controlled at least three times. Insights into the complex behavior of emulsions across different temperature stages can inspire the design of emulsions for specific applications.