Pickering emulsion stabilized with fibrous nanocelluloses: Insight into fiber flexibility-emulsifying capacity relations

Three types of nanocelluloses, including bacterial cellulose (BC), cellulose nanofiber (CNF) and cellulose nanocrystal (CNC), were used to prepare oil-in-water Pickering emulsions with the objective to disclose the effect of fiber flexibility on emulsification. In aqueous suspensions, the shortest CNC is rigid, while the longest BC fully flexible, which result in large difference in their dilute-to-semi-dilute concentrations, and in the rheological percolations. Thus, these cellulosic nanofibers play different roles during emulsification. Flexible BC nearly has no emulsifying capacity, whereas semi-flexible CNF and rigid CNC can be well used to stabilize emulsions. For the CNF-stabilized system, depletion effect is dominant, leading to the formation of droplet clusters easily, while for the CNC-stabilized one, repulsive effect plays more important role. Visible evidence regarding relaxation of long-term structure of droplets is further disclosed by dynamic rheology. This work proposes interesting views around tailoring morphology and viscoelasticity of Pickering emulsions by regulating fiber flexibility.