Thermally-induced phase fusion and color switching in ionogels for multilevel information encryption

• The thermochromic ionogels for information encryption and ionogel barcodes are presented. • The color switching of ionogels can be well controlled within a wide temperature range (32 to above 68 °C). • The ionogels exhibit exceptional stability in terms of size and optical properties . • By utilizing the ionogels, at least six levels of information encryption can be achieved. The growing significance of data security has propelled the advancement of information encryption materials. Here, thermochromic poly(4-hydroxybutyl acrylate) (PHBA) ionogels with broad response range and excellent cyclic stability were successfully developed through photopolymerization. Due to the reversible phase diffusion between PHBA polymer networks and ionic liquids (ILs), the PHBA ionogels can switch between opaque and transparent states in response to changes in heating temperature. The enthalpic and entropic properties of the PHBA ionogels were modified by adjusting the crosslinking density (1.0%–2.5%) of polymer networks and concentration (30%-60%) of ILs, which in turn accurately controlled their phase fusion temperature (32 °C to over 68 °C). The size and optical properties of ionogels can be effectively maintained even after exposure to surpass daily ambient temperatures (−10 and 50 °C) or humidity (75%) levels for 12 h, as well as undergoing heating–cooling cycles or operating in ambient environments for 60 days. These findings demonstrate the exceptional stability of these ionogels, rendering them suitable for application as reversible information encryption devices. For the first time, proof-of-concept demonstrations of a thermochromic ionogel system for six-level information encryption and ionogel barcodes are presented here. This work is particularly significant for smart soft materials and information encryption fields.