Nanomaterials-based Pickering foams: Stabilization, morphology, rheology, and perspectives

Increasing demand for foams in various industries and processes necessitates foams with high stability. However, the most widely used surfactants as foaming stabilizers are not sufficient to meet this requirement, particularly under extreme conditions. Recently, nanomaterials have emerged as an effective solution to improve foam stability, alter foam morphology, and control foam flow behavior. This review highlights key advancements in Pickering foams stabilized by various nanomaterials, which are categorized into three distinct types according to their spatial scale and structure: zero-dimensional (0D) nanomaterials (e.g., inorganic nanoparticles, organic nanoparticles, nanodots, etc.); one-dimensional (1D) nanomaterials (e.g., cellulose nanofibers, cellulose nanocrystals, chitin nanofibrils, etc.); and two-dimensional (2D) nanomaterials (e.g., graphene oxide nanosheets, molybdenum disulfide nanosheets, etc.). These nanomaterials work by stabilizing foam fluids at the interface and within the bulk liquid phase. The nanomaterials induce a shift from a liquid-like interface to a solid-like or gel-like state, altering the morphology of foams. The rheological properties of interface and bulk phase are intricately linked to the micron-scale structure of nanomaterials, ultimately dictating the rheology of foam fluids. Based on the special flow behavior of Pickering foams enhanced by nanomaterials, the mobility of liquid or gas in porous media can be controlled effectively. Finally, current applications of advanced nanomaterial-based Pickering foams are summarized, and the need for further exploration is underscored. The study holds promise to advance the creation of new nanomaterials and the expansion of applications for Pickering foams.