Dual cross-linked cellulose based hydrogel films†

Polymeric hydrogels and the associated structural assemblies are endowed with exceptional capabilities for applications in biomedicine, chemical biology, molecular electronics and wider energy paradigm. Cross-linking chemistry adds extra handles to tailor the gelation process and functional properties, surpassing those of traditional hydrogels. Here, we present molecularly tethered gelation of a cellulose (C) derivative by taking advantage of covalent and non-covalent interactions using organic and ionic linkers, respectively. The dual-cross-linked C-based hydrogels can be synthesized at a moderate temperature (∼70 °C) and processed into thin films using a programmable dip-coater at room temperature. The hydrogel films exhibited enhanced pH stability compared to the mono-cross-linked gels, were long-lived (over 180 days) and showed excellent ion-exchange properties. The gelation mechanism, local structures, and ion-exchange properties were corroborated by high-field (28.2 T, ¹H = 1200 MHz) solid-state NMR spectroscopy. A facile gelation process enabled by covalent linkages, metal coordination, and multimodal characterization demonstrated here is expected to provide opportunities for a number of unexplored applications.