Chitin nanocrystal-reinforced fluorescent carboxymethyl chitosan eutectogels

Carboxymethyl chitosan can promote heteroatom clusterization in eutectogels; • Chitin nanocrystals rigidify network and enhance clustering-triggered emission; • Eutectogels can be used for fruit spoilage detection and information encryption. Using polysaccharide nanocrystals to regulate networks is a promising way to open up more functions and application scenarios for the eutectogels. A chitin nanocrystals (ChNCs)-containing eutectogel was fabricated herein via a ‘two-step’ method for the study. Using carboxymethyl chitosan/poly(vinyl alcohol) as the matrices, the hydrogel networks were constructed via the freeze-thawing treatment and boronic esterification, and then underwent solvent exchange with glycerol/choline chloride. The as-obtained eutectogel has a well-defined structure, in which ChNCs act as a ‘reinforcing bar’ and boronic ester (B-O-C) bonding as a ‘bridge’, collaboratively strengthen the eutectogel networks. The strength (1.75 MPa) and modulus (0.65 MPa) are improved remarkably, enhancing by 38% and 55% than those of the eutectogels free of ChNCs and B-O-C bonds. Moreover, the clustering-triggered emission (CTE) capability of eutectogels is evidently enhanced because ChNCs can rigidify the eutectogel networks with the aid of B-O-C bonding. Therefore, the developed fluorescent eutectogel exhibits a variety of potential applications: encrypting specific information by tuning the heterogeneity of eutectogel patterns, monitoring fruit freshness by capturing the volatile substances released during spoilage, and perceiving strain/thermal alterations as a soft substrate. This work paves a feasible approach of using polysaccharide nanocrystals to construct the eutectogel-based multi-tasking platform.