Tunable Photonic Materials via Monitoring Step‐Growth Polymerization Kinetics by Structural Colors

Abstract

The functional and responsive properties of elastomeric materials highly depend on crosslink density and molecular weight between crosslinks. However, tedious analytical steps are needed to obtain polymer network structure–property relationships. In this article, an in situ structure–property characterization method is reported by monitoring the structural color change in a photonic elastomeric material. The photonic materials are prepared in a two‐step polymerization process. First, linear chain extension occurs via Michael addition. Second, photopolymerization ensures crosslinking, resulting in the formation of an elastomeric photonic network. During the first step, the step‐growth polymer process can be monitored by following the photonic reflection band redshift, allowing to program the molecular weight between the crosslinks. During network formation, the crosslink density, chain length between crosslinks, and the colors are “frozen in.” These processes can be locally controlled creating both single‐layered multicolor patterned and broadband reflective coatings at room temperature. The scalability of the coating process is further demonstrated by using a gravure printing technique. Additionally, the final coatings are made responsive toward specific solvents and temperature. Here the modulus, response, and color of the coating are controlled by tuning the crosslink density and molecular weight between crosslinks of the elastomeric material.

4D Chiral Photonic Actuators with Switchable Hyper‐Reflectivity

“…The CLCE is made using a two‐step crosslinking involving a base‐catalyzed thiol‐acrylate reaction and a light‐induced free radical polymerization reaction reported previously. [ 36–38 ] The CLC mixture is composed of 6 components ( Figure A). Monomer 1 is a liquid crystal diacrylate monomer and monomer 2 is a chiral dopant that induces the formation of the cholesteric liquid crystal phase.…”

Mechanochromism in Structurally Colored Polymeric Materials

“…[85,89,179] Increasingly, researchers are introducing other functionalities to photonic or plasmonic polymers, drawing from diverse areas of material science: examples include supramolecular selfhealing, [256] shape memory, [245,[250][251][252]257] and tunable moduli. [178] These designer materials could be particularly useful in areas such as soft robotics or electronic skins, [63,258,259] where polymeric components with bright, tunable color and the ability to self-repair for an improved product lifetime are highly desirable. It is certain that advances in structurally colored mechanochromic polymers such as these will drive the development of novel optical technologies, solving challenges across the fields of communications, optics, and sensing.…”

“…This result was attributed to the increase in surface roughness of the film that was caused by the roughness of the indenter. Gravure printing, another type of scalable roll‐feed printing, has also been used to produce patterned, stimuli‐responsive photonic materials, [ 178 ] and could be applied to mechanochromic LC materials in the future. In addition to thin films, microspheres of CLC elastomers can be produced by polymerizing emulsion droplets containing monomeric mesogens, with the LC ordering induced from the oil–water interface.…”

Rapid Fabrication of Alcohol Responsive Photonic Prints with Changeable Color Contrasts for Anti‐Counterfeiting Application

“…Similar RPPs in response to water or other stimulus can also be printed on cholesteric liquid crystals. [ 77–89 ] For example, Schenning's group [ 83,84 ] demonstrated that RPPs can be prepared by selective cross‐linking the cholesteric photonic film, which show reversible color under solvent or different temperature. Despite these successes, most of the fabricated RPPs show simple change in color contrast in response to the solvents.…”