Fluid Interfacial Engineering for Functional Materials: Pickering Emulsion-Mediated Interfacial Assembly

Abstract

Freestanding nanoparticle (NP) films with interconnected, porous architectures are highly attractive for advanced material applications due to their large surface areas and tunable structural features. Nevertheless, assembling NPs into cohesive films remains challenging, particularly when dealing with particles of high surface energy or structural heterogeneity, which often leads to aggregation and compromised integrity. Herein, we present a scalable approach to fabricate ultrathin, bicontinuous NP films using Pickering emulsion-mediated interfacial assembly. Our method facilitates the direct migration of jammed carbon NP networks from oil–water interfaces to air–water interfaces by leveraging catalytic bubble propulsion. This one-step process enables precise control over film dimensions and thickness while minimizing material loss and supporting reusability. The resulting films exhibit uniform NP packing, high mechanical robustness, and smooth transfer onto substrates with diverse geometries, such as micropatterned, stretchable, and complex three-dimensional surfaces. This enables the formation of conformal coatings that are well-suited for integration into flexible devices. In parallel, we introduce a complementary strategy that incorporates elastomeric polymers into the oil phase of Pickering emulsions to generate solidified composites with densely packed NP networks. By localizing barium titanate (BTO) NPs at the oil–water interface and inducing polymer curing, we produce mechanically stable, dielectric-enhancing microspheres. This method overcomes limitations of conventional polymer/NP composites that often suffer from particle aggregation and poor dispersion, which lead to leakage current and diminished capacitance. Furthermore, by tuning the internal phase ratio, we induce high internal phase emulsion (HIPE)-like morphologies that, upon solidification, result in hierarchically structured, freestanding porous solids. Together, these two approaches, involving interface-directed film formation and emulsion-templated microsphere assembly, highlight the versatility of fluid interfacial engineering in constructing functional NP architectures suited for applications that require both mechanical robustness and electrical performance.