Interfacial Materialization Enabled by Cellulose Nanofibril Surfactants

Biphasic liquid systems, serving as platforms with spatially directing functionality, achieve the integration of bio‐mass nano‐building blocks into advanced materials. Using liquid–liquid interfaces, a series of assemblies based on cellulose nanocrystals (CNCs) emerges, yet with limited application prospects, as the assemblies are mechanically fragile and thus incapable of withstanding processing‐induced stresses. Here, we propose flexible cellulose nanofibrils (CNFs) as alternative assembling blocks and exploit their interfacial assembly to construct functional materials. Through an interfacial co‐assembly strategy, CNFs spontaneously adsorb, assemble, and entangle at the water‐toluene interface, forming reinforced yet elastic interfacial multi‐layers. These assemblies are robust enough to yield multi‐dimensional constructs, such as 3D porous foams and 1D biocompatible filaments, with recyclable oil‐water separation and promising bioengineering applications.