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 its colour-changing behaviour. For instance, they exhibit electrochromic properties due to easy 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 through 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 elongation at break was 215%. After one hour, the recovery of FSR self-healing efficiency at 25 and 100 °C reached 98%. 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 application as redox-active and flexible electrochromic coatings.

This research was funded by the Russian Science Foundation (№ 23-23-00103).

References:

1. Zheng, R. et al. // ACS Appl. Mater. Interfaces 2018, 10, 35533–35538, doi:10.1021/acsami.8b13249.
2. Rashevskii, A.A. et al. // Coatings 2023, 13, 1282, doi:10.3390/coatings13071282.
3. Deriabin, K.V. et al. // Biomimetics 2023, 8, 286, doi:10.3390/biomimetics8030286.