Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures

Photoresponsive N-isopropylacrylamide ionogel microstructures are presented in this study. These ionogels are synthesised using phosphonium based room temperature ionic liquids, together with the photochromic compound benzospiropyran. The microstructures can be actuated using light irradiation, facilitating non-contact and non-invasive operation. For the first time, the characterisation of the swelling and shrinking behaviour of several photopatterned ionogel microstructures is presented and the influence of surface-area-to-volume ratio on the swelling kinetics is evaluated. It was found that the swelling and shrinking behaviour of the ionogels is strongly dependent on the nature of the ionic liquid. In particular, the [P6,6,6,14][NTf2] ionogel exhibits the greatest degree of swelling, reaching up to 180% of its initial size, and the fastest shrinkage rate (ksh = 29 ± 4 × 10-2 s-1).