Chameleon-like Self-Healing Flexible Materials Based on Ferrocenyl-Containing Polysiloxanes ^†

Animals such as chameleons change their skin colour in case of potential threat and recover damaged tissues [1]. Some ferrocenyl-containing polymers are similar to chameleon skin in terms of their colour-changing behaviour. For instance, they exhibit electrochromic properties due to an easily reversible one-electron redox transition [2].

Another feature of chameleons represented in polymer materials is their self-healing ability. One of the most promising self-healing materials is silicone rubber [3]. Some silicone materials possess self-healing properties achieved through siloxane equilibrium. This mechanism is based on reversible interactions between “living” anionic centres and polysiloxane chains [2,3].

The siloxane equilibrium discussed above allowed us to prepare unique chameleon-like ferrocenyl-containing silicone rubbers (FSRs) which exhibit both electrochromic and self-healing properties [2]. Thus, FSRs were obtained via ring-opening anionic copolymerisation of cyclic siloxane monomers including octamethylcyclotetrasiloxane (D₄), tetraferrocenyl-substituted cyclotetrasiloxane (1,3,5,7-(2-ferrocenylethyl)-1,3,5,7-tetramethylcyclotetrasiloxane, Fc₄D₄), and bicyclic cross-linking agent (bis-D₄). The physicochemical properties of the FSRs were estimated by tensile tests and cyclic voltammetry. As a result, the tensile strength of the FSRs reached 0.1 MPa, and the elongation at break was up to 215%. After one hour, the self-healing efficiency of FSR reached 98% at 25–100 °C. The FSRs also possess redox activity (Fc/Fc⁺ transformations at E⁰ = 0.43 V) and electrical conductivity at the level of antistatic materials (approximately 10⁻¹⁰ S cm⁻¹). The FSR films change their colour from yellow (reduced state) to blue (oxidised state). Our chameleon-inspired materials could find potential applications as redox-active and flexible electrochromic coatings.