Light responsive microstructural transitions in photo-responsive wormlike micelle mediated viscoelastic material based on cationic surfactant and photo-responsive organic acids

Abstract

Designing smart materials with fine-tunable structures and stimuli-tunable characteristics within a single molecule is a challenging task for the scientific community. This kind of materials circumvent limitations of conventional materials and are applicable in the formation of soft robotics, actuators, tissue engineering, optical devices, molecular switches and biosensors. In our efforts to design photo-responsive materials, herein we have designed photo-responsive wormlike micelle mediated viscoelastic materials (WMMVMs) through the synergistic interactions between the cetyltrimethylammonium bromide (CTAB) with photo-responsive organic acids (P-OA), i.e.,trans-cinnamic acid (t-CA) and p-coumaric acid (p-CA). Upon exposing the WMMVMs to UV light of 270 nm, drastic drop in viscoelasticity was observed because of the conversation of wormlike micelles in to rodlike micelles as the P-OAs are transformed from its trans form to cis form, confirmed through rheology and SANS. Further, the morphology of the system before and after UV irradiation was confirmed through SEM and TEM images. The irreversible photo-responsive character of the P-OA contributed to the irreversible photo-responsive behavior of the investigated systems. These systems bear good rheological behavior; specifically, Maxwell behavior. Additionally, these viscoelastic materials are also having excellent stretchability (20 times than its original length), self-healing (2 min) ability and higher thermal stability (>262 0C). WMMVMs also exhibited pH (below pKa) and temperature induced (CTAB/t-CA and CTAB/p-CA at 42 °C and 40 °C, respectively) reversible change in viscoelastic properties. We believe that the studied WMMVMs can serve as a useful model in understanding the process of photo-responsiveness and in various applications.