Second, we introduce materials based on the emulsions and discuss their potential applications, such as drug delivery, food, and composite materials. First, we outline several approaches for the preparation of the emulsions. This review summarizes recent advances in the Pickering emulsions stabilized with not only nanocelluloses, such as cellulose nanocrystals (CNCs), microfibrillated celluloses (MFCs), bacterial cellulose nanofibrils (BCNs), and TEMPO-oxidized nanocelluloses, but also microcrystalline cellulose (MCC). Moreover, surface modification of nanocelluloses can tailor wettability at the oil/water interfaces. These excellent mechanical properties play an important role in structurally stabilizing the interfaces. Given that the original crystal structure of cellulose microfibrils remains intact even after preparation, nanocelluloses have high modulus (130–150 GPa) and strength (2–6 GPa) and low coefficient of thermal expansion (4–6 ppm K −1) along the c-axis. The width, length, and surface properties of nanocellulose can be controlled by changes in cellulose sources and pretreatment: mechanical treatment only or with pretreatment, such as acid hydrolysis, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, carboxymethylation, phosphorylation, and enzymatic hydrolysis. Nanocelluloses are typically prepared through mechanical disintegration of bundles of cellulose microfibrils. Nanocellulose satisfies the increasing demands for a sustainable and environmentally friendly stabilizer for Pickering emulsions nanocelluloses efficiently stabilize oil/water interfaces due to their amphiphilic surface nature, which originates from the hydrophobic face and hydrophilic edge of cellulose chains. Solid particle at a planar oil/water interface. These unique characteristics and variability of Pickering emulsions may open up new opportunities for future emulsion-based materials. Surface modification can tailor the wettability of these fine particles, which can effectively change the emulsion phase between oil-in-water (o/w) and water-in-oil (w/o) emulsions (continuous phases are water and oil, respectively). Previous studies have dealt with fine organic or inorganic nanomaterials, including graphene oxide, carbon nanotube, carbon lamp black, laponite, montmorillonite, silica nanoparticles, calcium carbonate (CaCO 3), titanium dioxide (TiO 2), magnetic particles, and polymer particles. Various solid particles have been used as stabilizers for Pickering emulsions. The particles are strongly adsorbed at the interface, and the energy required to desorb the particle from the interface, or –Δ E, is orders of magnitude higher than that of soluble surfactants. As described by Equation 1, the adsorption is the strongest when θ = 90°. Where r and γ ow represent the radius of the particle and oil/water interfacial tension, respectively (see Figure Figure1). Equation 1 shows the change in interfacial energy, Δ E, when a solid sphere is adsorbed at the interface with a contact angle, θ, Unlike surfactant molecules, the particles irreversibly adsorb at liquid/liquid interfaces due to their high energy of adsorption, and therefore, the Pickering emulsion generally form more stable emulsion system than that stabilized by surfactants, which could provide great versatility in material processing. This type of emulsion is called Pickering emulsion. Solid fine particles have great potential as emulsion stabilizing agents. Therefore, surfactants are typically added to stabilize the system surfactants preferentially adsorb at immiscible liquid/liquid interfaces due to their amphiphilic properties, and suitable selection of surfactants leads to efficient reduction in the interfacial energy. However, these nano- and micro-emulsions show poor stability in most media due to their large interfacial areas. pharmaceuticals, cosmetics, food, fuel, and templates for other materials, such as porous material, liquid foam and emulsion films, and electrospun core–shell nanofibers and hollow nanotubes ). Hence, it offers remarkable potential for applications that need macroscopically homogeneous mixtures or efficient delivery systems (e.g. The system is optically isotropic, typically forming nano- or micron-ordered droplets throughout the system. An emulsion is a system consisting of two immiscible liquids, in which droplets of one liquid is dispersed in another.
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