The light-controlling of temperature-responsivity in stimuli-responsive polymers
Stimuli-responsive polymers are an important class of advanced materials that have lots of applications in biochemistry, biomedicine, optical memory, and cell labeling. The physical and chemical properties of these materials and also their surrounding media could be varied in response to environmental excitation. Temperature-responsive polymers are a significant category of smart polymers, displaying phase separation and cloud points in response to temperature variations in the solution state. Controlling such responses with light has become an interesting research area, because of the advantages of light-responsive materials for the reversible control of the physical and chemical properties of media in systems with tunable intensities. Photochromic compounds are some of the most important light-responsive materials used for the light-control of temperature-responsivity in light- and temperature-responsive polymers. The incorporation of photochromic compounds, such as spiropyran, azobenzene, diarylethene, and spiroxazine, in temperature-responsive polymers results in reversible light-induced variations of lower critical solution temperatures, upper critical solution temperatures, and phase separation temperatures in such systems. The incorporation of o-nitrobenzyl ester photoactive compounds in temperature-responsive polymers can result in irreversible light-induced variations of these characteristics. These variations originate from light-induced polarity changes in the systems resulting from the responses of the light-responsive compounds. Controlling the thermo-responsivity of dual light- and temperature-responsive polymers using light illumination is the main focus of this study, which is beneficial for the development of new dual- or multi-responsive polymers with potential applications in drug- and gene-delivery systems.