Scalable Pickering Stabilization to Design Cellulose Nanofiber-wrapped Block Copolymer Microspheres for Thermal Energy Storage

The only limitation to scale up the preparation of Pickering emulsion is the ultrasonication step. In this study, a scalable ultrasound-free approach was adopted to make a stable oilin-water (o/w) Pickering emulsion using cationic cellulose nanofibers (cNFs) as a stabilizer. The formation and stability of the emulsions were entirely dependent on the degree of cationic substitution (DS) in cNFs. Using such emulsions, we developed an aqueous dispersion of block copolymer (BCP)/cNF nanocomposite having the ability to store thermal energy. The BCP was prepared by reversible addition-fragmentation chain transfer ( RAFT) polymerization of stearyl methacrylate (SMA) followed by the polymerization of methyl methacrylate (MMA) in cNF-stabilized Pickering emulsion. The polySMA (PSMA) segment in the nanocomposite exhibited the ability to absorb and release thermal energy due to the side-chain melting and crystallization. The stability of the Pickering emulsion and nanocomposite latex along with the respective yields were greatly dependent on the DS in cNFs. Interestingly, the cNF-stabilized BCPs had the crystalline melting at 34-37 degrees C and crystallization at 22-28 degrees C with 12-fold higher latent heat than the BCP stabilized by sodium dodecylsulfate (SDS), a conventional surfactant.