Thermoreversible and tunable supramolecular hydrogels based on chitosan and metal cations

Abstract

A new thermoreversible and tunable hydrogel CS-M with high water content prepared by metal cation (M = Cu2+, Zn2+, Cd2+ and Ni2+) and chitosan (CS) was reported. The influence of metal cations on the thermosensitive gelation of CS-M systems were studied. All prepared CS-M systems were in the transparent and stable sol state and could become the gel state at gelation temperature (Tg). These systems after gelation could recover to its original sol state at low temperature. CS-Cu hydrogel was mainly investigated and characterized due to its large Tg scale (32–80 °C), appropriate pH range (4.0–4.6) and low Cu2+ concentration. The result showed that the Tg range was influenced and could be tuned by adjusting Cu2+ concentration and system pH within an appropriate range. The influence of anions (Cl−, NO3− and Ac−) in cupric salts in the CS-Cu system was also investigated. Scale application as heat insulation window was investigated outdoors. The different supramolecular interactions of the -NH2 group in chitosan at different temperatures were proposed to dominate the thermoreversible process of CS-Cu hydrogel.