Photo and temperature responsive novel surface active ionic liquid-based polymeric hydrogel

Abstract

Integrating more than two properties into a single polymeric hydrogel to introduce the multi-functionality has been a challenge for the scientific community in recent times. In order to impart photo and temperature responsive characteristics added with adjustable mechanical properties into the polymeric hydrogel, herein we have added newly synthesized photo-responsive ionic liquid (IL) into the polymeric (κ-carrageenan) hydrogel. The IL used is having morpholine-based ester functionalized long chain cation and azobenzene based anion that exhibited trans to cis transformation when irradiated by light of 465 nm for 50 min and show surface-active properties with CMC of 6.83 mM. IL with such photo and temperature responsive properties when mixed with the hydrogel of κ-carrageenan in KCl solution gives the photo and thermo-responsive hybrid hydrogel. The three-dimensional network structure of hydrogel made up of the ellipsoidal aggregates with major and minor axis radius of 9.3 A0 and 1.6 A0, respectively is made up of a fibrous porous structure and gets disrupted through the light irradiation and initiated the gel to sol transition, studied through the SEM images, DLS data and rheological measurements. The (IL) based hydrogel gets disrupted after light irradiation as the anion of the IL starts transforming from trans to cis isomerization. Also, the thermo-reversible transition of hydrogel within room temperature to 54 °C is also shown by rheology. Kinetics of the trans to cis transformation, controlled strain and stress measurement and thermal stability of the hydrogel are assessed here. The studied photo and temperature responsive hydrogel could start a new range of smart materials.