Easily-processable and programmable responsive semi-interpenetrating liquid crystalline polymer network coatings with changing reflectivities and surface topographies

\u3cp\u3eThe fabrication of stimulus-responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily applied reflective coating based on a semi-interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.\u3c/p\u3

Stimuli-responsive polymer film or coating prepared by mixing in a suitable fashion a side chain liquid crystalline polymer with reactive mesogens and responsive devices:process for preparing the same

The limitation of the different classes of responsive liquid crystals such as volatility in case of low molecular weight liquid crystals (LMWLCs) can be overcome by the development of a responsive film based on polymerliquid crystals (PLCs) and reactive mesogens (RMs or reactive liquid crystal monomers) to create a responsive film or coating material which appears to be easily alignable and processable. That coating material shows a large response of which the properties can be tuned in a modular approach. In this way, the advantages of both materials, PLCs and RMs, were combined, yielding stable films, which can be aligned when desired and which stimuli- responsive properties can be tuned by the choice of RMs. Thus mixtures of PLCs with RMs open the doors to a wide variety of stimuli-responsive coating systems, without the need of time consuming trial-and-error synthesis of PLCs and closed liquid crystal cells. By choosing chiral RMs, cholesteric LC coatings can for instance be fabricated, while a light responsive RM could provide a light responsive coating. In addition, one could use similar methods as were used for LMWLCs with RMs in closed cells to prepare for example broadband reflectors or patterned coatings that change topography by a stimulus

Environmentally responsive photonic polymers

\u3cp\u3eStimulus-responsive photonic polymer materials that change their reflection colour as function of environmental stimuli such as temperature, humidity and light, are attractive for various applications (e.g. sensors, smart windows and communication). Polymers provide low density, tunable and patternable materials. This feature article focusses on various autonomously responding photonic polymer materials such as hydrogels, block copolymers and liquid crystals and discusses their potential industrial implementation.\u3c/p\u3

Temperature-responsive, multicolor-changing photonic polymers

\u3cp\u3eA new principle is developed to fabricate temperature-responsive, multicolor photonic coatings that are capable of switching color. The coating is composed of a non-cross-linked liquid crystal siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixing between the siloxane and the acrylate polymers and change the reflective colors correspondingly. The temperature-responsive color change of the coatings can be programmed by the processing conditions and coating formulation, which allows for the fabrication of photopatterned multicolor images. The photonic ink can be coated on flexible poly(ethylene terephthalate) films using roll-to-roll flexographic printing, making these temperature-responsive, multicolor-changing polymers appealing for applications such as responsive color decors, optical sensors, and anticounterfeit labels.\u3c/p\u3

Temperature-responsive polymer wave Plates as tunable polarization converters

\u3cp\u3eA temperature-responsive polarization converter, which reversibly changes from a full-wave to a half-wave plate upon heating, is developed. The polymer wave plate has a controlled thickness and is based on a uniaxial aligned nematic semi-interpenetrating network coating containing a specific concentration of a non-crosslinked liquid crystal elastomer. Upon heating, the effective birefringence of the wave plate halves without changing the thickness. The function of the wave plate is demonstrated by sandwiching the tunable polarization converter between two identical right-handed circular polarized light reflective films with a wavelength around 770 nm. At low temperatures, this optical device reflects 50% of light at 770 nm, whereas at elevated temperature 81% is reflected. Such temperature-responsive optical devices have potential applications for both aesthetic purposes as well as energy saving windows.\u3c/p\u3

3D helix engineering in chiral photonic materials

\u3cp\u3eEngineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super-reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left- and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti-counterfeit labels and data encryption to aesthetics and super-reflective films.\u3c/p\u3

An easily coatable temperature responsive cholesteric liquid crystal oligomer for making structural colour patterns

\u3cp\u3eA crosslinkable cholesteric main-chain liquid crystal oligomer was prepared, and coated on glass using blade-coating. The coating showed a reflection band that varied as a function of temperature over a range of several hundreds of nanometers. This allowed patterning of the coating in various colours using multiple crosslinking steps at different temperatures.\u3c/p\u3

Easily processable temperature-responsive infrared-reflective polymer coatings

\u3cp\u3eA temperature-responsive near-infrared reflective coating was fabricated based on a side-chain liquid crystal siloxane polymer using a simple wired-bar method. The cholesteric liquid crystalline polymer film showed a blue shift of the reflection band of 1000 nm in the IR region upon heating. The temperature-responsive change of the reflection band was reversible. Compared to that of the same mixture system in an alignment cell, the coating showed a significantly faster response. This research demonstrates an easy way to prepare a temperature-responsive IR-reflective coating that shifts its reflection to a shorter wavelength upon heating. As IR radiation of shorter wavelengths is more strongly represented in sunlight than longer wavelengths, this coating could be used to selectively reduce heating of an indoor space when the temperature is high. This is promising for the future application of smart climate control.\u3c/p\u3

Photonic time-temperature sensor having an embossed interpenetrating network of cholesteric liquid crystalline polymers and a secondary polymer

Photonic time-temperature sensor consisting of an embossed interpenetrating network of a cholesteric liquid crystalline polymers and a secondary polymer. Preferably in which the secondary polymer is orthogonal and is not covalently attached to the interpenetrating network, but physically interpenetrated therein. For use as food sensor for checking freshness of the food