This study introduces a promising approach to stabilize high internal phase emulsions (HIPEs) in which droplets are enveloped by octadecane (C18)-grafted bacterial cellulose nanofibers (BCNFdiC18), which are mainly surrounded by carboxylate anions and hydrophobically modified with C18 alkyl chains. For this purpose, BCNFdiC18, in which two octadecyl chains were grafted onto each of several cellulose unit rings on 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidized BCNFs, was fabricated using the Schiff base reaction. The wettability of BCNFdiC18 was adjusted by controlling the amount of the grafted C18 alkyl chain. Interfacial rheological analysis revealed that BCNFdiC18 enhanced the membrane modulus at the oil–water interface. We figured out that such a resilient interfacial membrane substantially prevented interdrop fusion across the water drainage channel formed between the jammed oil droplets, which was confirmed theoretically using the modified Stefan–Reynolds equation. These findings highlight that the use of surfactants in the form of nanofibers to form a rigid interfacial film plays a key role in hindering the interfusion of the internal phase and the collapse of the emulsion, which is essential for HIPE stabilization.

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Benefiting from the demixing of substances in the two-phase region, a smart polymer laminate film system that exhibits direction-controlled phase separation behavior was developed in this study. Here, nanoemulsion films (NEFs) in which liquid nanodrops were uniformly confined in a polymer laminate film through the layer-by-layer deposition of oppositely charged emulsion nanodrops and polyelectrolytes were fabricated. Upon reaching a critical temperature, the NEFs exhibited a micropore-guided demixing phenomenon. A simulation study based on coarse-grained molecular dynamics revealed that the perpendicular diffusion of oil droplets through the micropores generated in the polyelectrolyte layer is crucial for determining the coarsening kinetics and phase separation level, which is consistent with the experimental results. Considering the substantial advantages of this unique and tunable two-dimensional demixing behavior, the viability of using the as-proposed NEF system for providing an efficient route for the development of smart drug delivery patches was demonstrated.