Unveiling Spinodal Decomposition‐Driven Phase Separation of Cellulose Nanofibrils‐Reinforced Nanoemulsion Films for In Situ Thermoset Curing

Abstract Herein, a temperature‐responsive nanoemulsion film (NEF) system is introduced with spinodal decomposition for in situ thermoset curing. The NEFs, fabricated by alternate layering of nanoemulsion droplets with bacterial cellulose nanofibrils (BCFs) and polyelectrolytes through the layer‐by‐layer (LbL) deposition, show ≈32% increase in Young's modulus compared with those fabricated with polyelectrolytes only. It is determined that such reinforcement stemmed from the presence of BCFs that form fibrillary layers in the NEF matrix. The BCF‐reinforced NEFs show the unprecedented spinodal decomposition behavior; nanoemulsion droplets uniformly dispersed in the NEF network and readily interdiffused to produce microscale oil domains with controlled phase separation rate as well as oil domain size. The insight gained from the thin film‐based microphase separation behavior confirms that NEFs layered with epoxy resin nanoemulsions are materials with promising temperature‐responsive in situ thermoset curing performance.