Polymerized liquid crystals as actuators and sensors

Novel liquid-crystalline polymers that respond to specific stimuli by changing their shape or color can be used as soft actuators and optical sensors for environmental, energy, and biomedical applications

Cholesteric liquid crystalline polymer networks as optical sensors

In the past decade, chiral nematic liquid crystals (LCs) have emerged as an attractive material for the development of stimuli-responsive systems (White et al. 2010; Ge and Yin 2011; Fenzl et al. 2014; Mulder et al. 2014; Stumpel et al. 2014). Due to the periodic alteration of their refractive indices, they act as one-dimensional photonic structures and reect circularly polarized light of same handedness. The reection of light is governed by Bragg’s law: λ θb = nP cos where λb is the wavelength of Bragg reection, n is the average refractive index, and P is the length of the helical pitch. The pitch of a chiral nematic is dened as the length traversed by the molecular director nˆ on 360° rotation (Figure 4.1a). It is inversely proportional to the concentration [C] as well as the helical twisting power

Full color camouflage in a printable photonic blue-colored polymer

\u3cp\u3eA blue reflective photonic polymer coating which can be patterned in full color, from blue to red, by printing with an aqueous calcium nitrate solution has been fabricated. Color change in the cholesteric liquid-crystalline polymer network over the entire visible spectrum is obtained by the use of nonreactive mesogen. The pattern in the coating is hidden in the blue color dry state and appears upon exposure to water or by exhaling breath onto it due to different degrees of swelling of the polymer network. The degree of swelling depends on the printed amount of calcium which acts as a cross-linker. The printed full color pattern can also be hidden simply by using a circular polarizer. The responsive full color camouflage polymers are interesting for various applications ranging from responsive house and automobile decors to anticounterfeit labels and data encryption.\u3c/p\u3

Liquid crystal dye mixture

A guest-host liquid crystal dye mixture comprising a calamatic, thermotropic liquid crystal as host and a dichroic fluorescent dye as guest, characterized in that the dichroic fluorescent dye is a multichromophoric dye containing at least a group with the general formula Ry - X1 - C1, wherein Ry is a chromophore from the rylene family, C1 is a second chromophore and X1 is a spacer that interrupts the conjugation between Ry and C1, the spacer X1 is selected such that it introduces rigidity against bending or folding over an axis perpendicular to the length of the molecule

Preface

Not available

A full color photonic polymer, rewritable with a liquid crystal ink

\u3cp\u3eA printable and rewritable photonic polymer coating has been fabricated from a cholesteric liquid crystal. Full color images can be patterned in polymer coatings by using a liquid crystal ink. The printed patterns can be erased and rewritten multiple times, making these coatings interesting as rewritable papers.\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

Infrared regulating smart window based on organic materials

Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year. Moreover, we place emphasis on windows that maintain transparency in the visible region so that additional energy is not required to retain natural illumination. We discuss a number of ways to fabricate windows which remain as permanent infrared control elements throughout the year as well as windows which can alter transmission properties in presence of external stimuli like electric fields, temperature and incident light intensity. We also show the potential impact of these windows on energy saving in different climate conditions

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