Dynamics of Surfactant-Functionalized Nanoparticle Assembly during Bicontinuous Particle-Stabilized Emulsion Formation

Abstract

In situ functionalization of nanoparticles by surfactants is a versatile strategy to stabilize bicontinuous interfacially jammed emulsion gels (bijels). However, the dynamic and composition-dependent nature of surfactant adsorption complicates the reproducibility of kinetically determined formation. While prior research has primarily correlated the precursor composition with the final bijel morphology, the underlying formation dynamics have not yet been fully elucidated. This paper investigates the formation of bijels fabricated via solvent transfer-induced phase separation (STrIPS). To explore how surfactants can affect the formation kinetics, we investigated the combination of silica nanoparticles functionalized with cetyltrimethylammonium bromide (CTAB). Using in situ (ultra)small-angle X-ray scattering and ex situ confocal microscopy, we show that higher CTAB concentrations accelerate both liquid-liquid phase separation and nanoparticle self-assembly, shortening the bijel formation time from 600 to 250 ms. Moreover, we find that initially self-assembled particles can rearrange or disassemble during phase separation depending on the CTAB concentration. Analysis of the particle interactions in precursor mixtures, supported by theoretical modeling, proposes a correlation between interparticle forces and the final bijel morphology. These findings highlight the importance of understanding the formation dynamics to control the bijel structure and enhance their reproducibility. The obtained insights into phase separation and particle assembly are important to advance biosynthesis in applications like catalysis and energy storage.