Light‐Responsive Smart Soft Matter Technologies

Abstract

Elegant natural phenomena triggered by light are widespread in our everyday environment. Human vision is enabled by such a light-driven process, i.e., photoisomerization of retinal. Phototropic and heliotropic motions in plants (e.g., sunflowers pivoting their faces to follow the sun) are driven by photoisomerization of phytochromes. These light-triggered processes occurring in nature have served as great inspiration for scientists and engineers and as a consequence, a variety of light-responsive functional materials and systems have been explored both scientifically and evaluated for potential in a wide range of technological applications. Soft materials, including liquid crystals, polymers, gels, and biological materials, endowed with photoresponsiveness have recently emerged as multifunctional advanced optical materials for diverse applications. The great interest in such systems arises from their unique combination of contactless energy delivery with the ability to modulate at high spatial and temporal resolution. The explosion of low-cost light sources with tunable wavelength/frequency, intensity and chirality has enabled a new toolbox of stimulus variables. The dynamic attributes of these soft materials have been exploited in the fabrication of photoswitchable and reconfigurable materials and systems with programmable properties and functions. This has enabled the development of a variety of new light-driven soft matter technologies involving molecular switches/motors, shape morphing materials, alignment methods etc. The applications of such technologies range from simple on-off switching to sophisticated soft robotics and 3D & 4D printing. In this special issue, significant recent developments of various light-driven phenomena and their applications in soft material systems are covered. A wide range of topics that convincingly illustrate the richness of this vibrant research field are presented by leading experts. Optical control over bio-interfaces with the help of azo-dye containing soft materials is a promising approach in cell biology and tissue engineering. In their article, Christopher J. Barrett and co-workers (DOI:10.1002/adom.201900091) present various developments on the use of photo-reversible azo-based soft materials in this context. They describe using light to control molecular motion of photoactuating surfaces and patterns for bio-interface applications. Modulation is enabled by light-driven photoorientation, topological patterning, and photomechanical actuation. Stefano Palagi and co-workers (DOI:10.1002/adom.201900370) discuss wirelessly powering and controlling mobile microscale devices and microrobots using light as a versatile stimulus. They have analyzed the behaviors of two interesting classes of stimuli-responsive polymeric materials, i.e., poly(N-isopropylacrylamide) hydrogels and liquid crystal elastomers, in microrobotics and highlighted their recent applications. They also emphasize the significance of a structured light field in driving soft microrobots fabricated from light-responsive polymeric materials. 2D materials are known to exhibit exceptional physical and chemical properties which qualify them as candidates for modern technological applications. Paolo Samorì and co-workers (DOI:10.1002/adom.201900286) report on the functionalization of 2D materials with light-responsive molecules. They discuss functional hybrid systems possessing tunable optical properties and their applications in photoswitchable electronic devices. Supramolecular polymers exhibit certain distinct characteristics when compared to their synthetic and biopolymer counterparts where the monomers are covalently linked. Da-Hui Qu, He Tian and co-worker (DOI:10.1002/adom.201900033) summarize new developments in light-responsive supramolecular polymers capable of exhibiting novel functions and applications beyond disassembly and reassembly. They discuss light controlled morphology transformations including programmed shape