Photoinduced Ultrafast Shape-Changing Self-Assembled Arylazopyrazole-Based Polymeric Micelles

Abstract

In recent times, photoinduced shape-changing polymers have demonstrated great potential in various applications. The solvent-dependent/free photochromism and conformationdependent shear viscosity modulation of the developed materials enhance their relevance from industry to academia. Here, two hydrophobically modified photoresponsive arylazopyrazole-based copolymers have been developed via reversible addition−fragmentation chain-transfer (RAFT) polymerization technique using hydrophilic poly(ethylene glycol) methyl ether methacrylate [PEGMA] moieties. The nonsubstituted arylazopyrazole-based copolymer has a shorter half-life that fosters the development of the difluorosubstituted copolymer with a longer half-life. Both copolymers exhibit self-assembly behavior in water to form micelles, as has been evidenced by photoluminescence spectroscopy and surface morphological analyses. Upon UV light exposure, both copolymeric micelles photoisomerize from trans-state to cis-state. The electron microscopic analyses (both FESEM and TEM) can detect that the shape-changing morphology has been perceived from spherical to deformed spherical only for the difluoro-substituted copolymer. Rheological studies reveal the impact of photoisomerization-induced changes in the hydrophobicity of two arylazopyrazoles on solution aggregation. Two distinct photoinduced glass transition temperatures and phase transition temperatures of both copolymers have been evidenced by differential scanning calorimetry (DSC). The study offers a new finding toward the impact of varying the hydrophobicity of stimuli-responsive end groups on aggregation and viscoelastic behaviors. Nevertheless, it is essential to mention that the extended thermal half-life of the developed material advances its applicability in smart devices for biomedical sciences optics, coating, energy storage, and so on.