Well-Adhering, Easily Producible Photonic Reflective Coatings for Plastic Substrates

Abstract

The development of well-adhering, easily producible photonic reflective coatings is still a challenge. Here, an easy-to-produce, industrial viable process is reported that uses a primer layer of the so-called type II photoinitiator to obtain an excellent adhesion between a plastic substrate and one-dimensional (1D) photonic liquid crystalline coatings. Furthermore, a good alignment of the reactive cholesteric liquid crystal mixture is obtained using a bar-coating process, without alignment layers or surfactants. After photopolymerization, cross-hatch tape tests show a good adhesion of the photonic coating having a reflection band of 50% transmission with almost no scattering. Additionally, we demonstrate the ability to create well-adhering ∼100% reflective coatings by coating double layers and the ability to create single-layered cholesteric broadband reflectors using solely a reactivity gradient created by the primer layer. Our new interfacial method gives new opportunities to use reflecting 1D photonic coatings in industrial processes and applications and allows the bonding of almost any polymer to a plastic substrate.

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

“…A Ch‐LC mixture was prepared consisting of 20 wt% dithiol 1 , 7 wt% chiral dopant 2 , 70 wt% diacrylate 3 , 1 wt% photoinitiator benzophenone (BP), and 2 wt% catalyst triethylamine (TEA) ( Figure A). For the formation of the elastomeric Ch‐LC coatings, a two‐step thiol–acrylic polymerization mechanism was used after bar coating with the Ch‐LC mixture, which aligned the LCs uniformly by shear alignment . In the first polymerization step, only chain extension of the monomers occurs by linear step‐growth polymerization.…”

“…For the formation of the elastomeric Ch-LC coatings, a two-step thiol-acrylic polymerization mechanism was used after bar coating with the Ch-LC mixture, which aligned the LCs uniformly by shear alignment. [30] In the first polymerization step, only chain extension of the monomers occurs by linear step-growth polymerization. Afterward, the linear oligomers are cured into a network ( Figure 1B).…”

“…Mater. 2020, 30,1906833 times and reveals a significant redshift as the reaction progresses. After 4 h at room temperature, the reflection band has shifted from blue (440 nm) to red (650 nm), keeping a good LC alignment.…”

Flexible Multifunctional Sensors for Wearable and Robotic Applications

“…As highlighted above, the relationship between the helical pitch and the reflection wavelength can be described in Equation (12); thus, the lasing wavelength was tuned by mechanical strain. [192,193] Recently, Schenning et al proposed a new material system that is well-adhering, which can easily produce CLCEs including reactive mesogens, crosslinkers, and photoinitiators; see Figure 14. Currently, the lasing wavelength can be tuned across the whole visible region from blue to red (≈450-650 nm).…”

“…Inspired by this pioneering work, a variety of dyes have been intensively explored for developing a boarded tunability of lasing wavelength. [192] The transparent mixture was bar-coated over a polycarbonate substrate, and subsequently photopolymerized, resulting in a highly molecularly aligned CLCE that were welladhered to the substrate shown in Figure 14d. [185] After the discovery of tunable lasing in CLCEs, Shibayev et al in 2010 came up with the novel concept that the mechanical tunability of a photonic bandgap can be used for next-generation mechanical sensors, allowing one to visualize a mechanical stress due to the change of light reflection wavelength.…”