Photonic Shape Memory Chiral Nematic Polymer Coatings with Changing Surface Topography and Color

Abstract

optical time-analyte indicators. [21,22] Regular surface topographies exhibiting structural colors have been fabricated in SMPs by top-down methods including locally induced surface wrinkling, [23] nanoimprint lithography, [24,25] compression molding, [26] or templating via microspheres. [27] In these examples, hot pressing of the surface features results in a temporary flattened and colorless state, which is reversible upon heating. [24][25][26][27] To circumvent the cumbersome topdown nanoforming steps to generate the structural color, photonic SMP coatings generated by bottom-up self-assembly have also been employed. [17,28,29] For example, shape memory photonic films have been produced from core-interlayer-shell polymer microspheres that form opal structures. [30][31][32] Alternatively porous inverse-opal SMPs have been templated by silica colloids. [33] Capillary pressure-induced "cold" programming of these materials results in a disordered temporary state consisting of collapsed pores and an arbitrarily roughened surface, which can be recovered by pressure, heat, organic vapors, solvents, and microwave radiation. [34][35][36][37][38][39] Unfortunately, the fabrication of such SMP coatings is still hampered by the lack of facile methods and materials. [40] Reactive liquid crystalline materials are exciting from this perspective since they form nanostructured phases via selfassembly, and can be easily processed via photopolymerization [41][42][43][44] to fabricate polymeric coatings. [45][46][47][48][49] Chiral nematic liquid crystalline (a.k.a. cholesteric liquid crystalline (CLC)) phases are of particular interest for their periodic helical structures which lead to the selective and incident-angledependent reflection of light, resulting in iridescent structural colors. [50] CLC coatings have been reported that respond to stimuli including heat, light, and humidity. [17,[51][52][53][54][55][56][57] In addition, CLC coatings have been reported that simultaneously change surface topography and color in a reversible manner. [41,55] Recently, our group reported that irreversible thermoresponsive photonic coatings can be fabricated based on CLC polymer networks using a shape memory approach. [58,59] Indentation of a small area (≈1 mm 2 ) of the CLC film, at a temperature above the T g of the polymer network, resulted in a blue-shift of the reflection band through a reduction of the pitch of the cholesteric helix, which was fully recovered upon heating.We now report a new approach for the fabrication of shape memory photonic coatings that irreversibly change both topography and color. Polymeric CLC films with a red structural The fabrication of shape memory coatings that change both reflectivity and topography is hampered by the lack of facile methods and materials. Now, shape memory photonic coatings are fabricated by high-speed flexographic printing and UV-curing in air of a chiral nematic liquid crystal ink. Deformable polymeric films with a red reflection band and a smooth surface topography are obtained which...

Brush‐Paintable, Temperature and Light Responsive Triple Shape‐Memory Photonic Coatings Based on Micrometer‐Sized Cholesteric Liquid Crystal Polymer Particles

“…[ 11–15 ] In contrast, photonic paints, in principle, are able to generate both structural colors and topographical changes. [ 16–21 ] Such paints are useful to adjust surface wettability and adhesion and/or the reflective and aesthetic properties of a coating. Photonic paints usually require delicate processing to promote the formation of the photonic nanostructure, [ 21–23 ] and brush or spray‐painting is not possible.…”

“…[ 16–21 ] Such paints are useful to adjust surface wettability and adhesion and/or the reflective and aesthetic properties of a coating. Photonic paints usually require delicate processing to promote the formation of the photonic nanostructure, [ 21–23 ] and brush or spray‐painting is not possible. Recently, structurally blue colored silica spheres have been reported as photonic pigments that can be mixed with a binder to form static photonic paints that can be brush‐painted.…”

Self-Avoiding Random Walks as a Model to Study Athermal Linear Polymers under Extreme Plate Confinement

“…Polymer based thin films have been used extensively for several decades in a varied range of applications from optical coatings and energy storage to smart appliances, semiconductors and pharmaceutics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Further inclusion of nanoparticles or adhesion to complex interfaces allows efficient control, tuning, and magnification of the already exceptional base macromolecular properties.…”

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

“…Elastomeric polymers have been investigated intensively over the past years for the creation of stimuli‐responsive materials. In particular, the combination of the anisotropic nature of liquid crystals (LCs) and the flexibility of elastomer networks have proven to be an excellent combination for shape memory films, soft actuators, and stimuli‐responsive materials . Having control over the polymerization reaction by controlling crosslink density and molecular weight between crosslinks is highly desired to create optimal functionality, flexibility, and strength in the material …”

“…[20] Especially the latter, involving Michael addition, has received a lot of interest recently, due to the large variety of reactive mesogens that are available. [1][2][3][4][5]8,13,14,21,22] By controlling the network formation, a large variety of stimuli-responsive shape and color changing materials with desired functional properties can be obtained. [23] Stimuli-responsive photonic materials that are able to change their color are appealing for applications such as sensors, energy-saving windows, and security labels.…”