Bidirectionally Modulating the Dissipative Phase Transition of UCST Polymers in a Programmable Manner Using Visible Light

Abstract

Dynamic phase transitions are important in living organisms for sustaining their adaptive structures and functions. The design of artificial dynamic systems using light as a noninvasive input fuel has gained significant interest to mimic such adaptive features. Here the development of light‐fueled dissipative phase transitions of upper critical solution temperature polymers by introducing pendant spiropyrans as photoactive units, is reported. The reversible open‐close photoisomerization of spiropyrans is designed to undergo either an enhancement or a decline of their net charge, which is subsequently used to regulate the electrostatic interactions between polymer chains, and ultimately shift their phase transition temperatures to either a lower or a higher direction. The degree and speed of such bidirectional shifting are flexibly modulated by manipulating the external illumination parameters or varying the compositions/concentrations of the polymers. The diametrically opposite transmittance changes driven by light are utilized to produce a series of complementary patterns and shapes for application in transient information storage and encryption with improved accuracy and security. This work offers a bidirectional spatiotemporal modulation of dissipative phase transitions of polymers using visible light that allows highly tunable and adaptable features shared with their natural counterparts.

A Paper‐Like Hydrogel for Versatile Information Encryption and Decryption Via Chemical‐Induced Phase Separation

“…[20] Although hydrogel-based information storage using chemical color is highly designable and can be achieved by means of a wide range of stimuli, such as light, [21] electricity, [22] heat, [23] pH, [24] and lanthanide ions or other chemicals, [12,[25][26][27][28] it generally demands a specific material design and synthesis by incorporating responsive species (e.g., chromophores) that usually react to a single stimulus, limiting the versatility. As for hydrogel information storage based on physical color, most studies use polymers that undergo thermally induced phase separation on heating (LCST) or cooling (with an upper critical solution temperature: UCST), including PNIPAM, [29] poly(2-isopropyl-2oxazoline), [21] poly(acrylamide-co-acrylonitrile) [30] and polyacrylamide (PAAm), [31] to realize optical transmittance change. Thermally responsive hydrogels are easy to prepare, with temperature as the primary stimulus for the physical color adjustment.…”

Multiresponsive Bilayer Hydrogel Actuator with Switchable Shape Morphing Capability and Visible Color/Fluorescence Change

“…Nature serves as an eternal source of inspiration; creatures like chameleons, frogs, and diverse plant species such as mimosa and Venus flytraps exhibit remarkable abilities to manipulate their color, volume, shape, and morphology toward external stimuli. − They employ these capabilities for purposes such as camouflage, communication, and predation, which inspire humans to explore the development of artificial intelligence materials capable of responding to environmental stimuli. − Among them, stimulus-responsive hydrogels have emerged as versatile tools in the realm of smart materials. − Multistimulus-responsive bilayer hydrogels that are capable of shape morphing and/or color alterations in response to external stimulus (such as variations in light, temperature, salt concentration, electric fields, etc.) have paved the way for diverse applications. − These bilayer hydrogels find utility in areas such as switches, microrobots, and smart windows, unlocking a multitude of possibilities. − …”