Chitin nanocrystal-stabilized Pickering emulsion for multimodal sensing

A Pickering emulsion-templating method is developed for preparing composite hydrogels with improved mechanical properties and ionic conductivity. First, an aqueous system with poly(trimethylolpropane triacrylate) microspheres coated with chitin nanocrystals (ChNCs) is prepared using an oil-in-water emulsion template by means of photo-cross-linking. Thereafter, the system is mixed with poly(vinyl alcohol) (PVA) and borax solutions, followed by freeze-thawing treatments. The as-prepared hydrogels exhibit two types of characteristic cross-links, physical cross-links caused by the crystallization of PVA, and chemical cross-links caused by the occurrence of boronic ester (B-O-C) bonding between PVA chains and ChNC-coated microspheres. Microspheres serve to simultaneously reinforce and plasticise the hydrogel system. The strength and elongation of the microsphere-containing hydrogel are 676 kPa and 600 %, respectively, considerably higher than those of the microsphere-free hydrogels (350 kPa and 350 %). The volume exclusion effect of microspheres also enhances ionic conductivity, resulting in improved strain and thermal resistances. Therefore, the emulsion-templated hydrogel sensor is deemed more suitable for probing deformation with large strain in comparison with the microsphere-free hydrogel sensor. This study proposes an effective way of using ChNC-stabilized Pickering emulsions to template mechanical properties and sensing abilities of hydrogel-based strain sensor.