UV Curable Robust Durable Hydrophobic Coating Based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSS) and Their Derivatives.

Hydrophobic coatings have considerable potential applications in many fields. Ease of operation and high durability are essential for practical use. Fast curing and being solvent-free are a plus, and if they possess certain characteristics (antigraffiti, good adhesion, high hardness, heat resistance, wide range of applicability, etc.) at the same time, it is a dream solution. Herein, a facile one-step approach with the above features was reported for a UV curable robust hydrophobic coating based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSSs). The structure and surface morphology of these EP-POSSs and their derivatives were systematically studied. Because of the core-in-cage structure which was constructed by repeating units of R-Si(O1/2)3 and the strong covalent bonds of Si-C and Si-O, the coatings displayed high pencil hardness (6-8H), high thermal stability with initial decomposition temperature around 350-400 °C, and a high water contact angle (up to 108.06°) even after outdoor exposure for a month. These POSSs and their derivatives are expected to find uses in various applications such as stain resistance, self-cleaning, scratch resistance, and cigarette moxibustion resistance of wood furniture, kitchenware, and medical and industrial appliances.

Actuation performance of a liquid crystalline elastomer composite reinforced by eiderdown fibers.

Liquid crystalline elastomer (LCE) materials have been developed and investigated for several decades. One important obstacle, which impedes the practical industrial application of LCE materials, is their modest robustness as actuator materials. In this work, we developed a LCE composite which was fabricated by incorporating eiderdown fibers into a polysiloxane-based main-chain LCE matrix. The eiderdown fibers were used as the flexible reinforcement phase suitable for the shape-morphing performance of LCE materials upon being stimulated. Due to the long fiber property, specific structure and surface characteristics of the eiderdown fibers, they constructed a reinforcement network in the LCE matrix and formed tight interfacial adhesion with the matrix. The LCE composite demonstrated enhanced actuation mechanical properties and robust actuation performance. Its actuation blocking stress and modulus were increased due to the reinforcement effect of the eiderdown fibers. The tensile strength and the performance of anti-fatigue failure under repeated actuation cycles and high loadings were greatly improved due to the crack-resisting effect and bridging effect of the eiderdown fibers. While other properties, such as the liquid crystalline phase structure, the stimulus deformation ratio, phase transition temperature of the LCE matrix, etc., did not deteriorate or change due to the high flexibility, thermal stability and chemical stability of the eiderdown fibers.

Optical Wavelength Selective Photoactuation of Nanometal-Doped Liquid Crystalline Elastomers by Using Surface Plasmon Resonance.

Photoactuated liquid crystalline elastomer (LCE) materials are gaining much attention in many application fields, but challenges for the precise modulation of their photoresponses still exist. Researchers have explored various optical parameters, such as polarization, intensity, and wavelength, to obtain differential responses. The development of photoactuated LCE materials with wavelength-selective responsiveness is more versatile and has attracted more interest, but such LCE materials are commonly prepared by incorporating different molecular chromophores or dyes into the LCE matrices. When the surface plasmon resonance (SPR) characteristic of nanometals, which can generate strong photothermal conversion, and the difference of SPR absorption wavelength bands of different nanometals are considered, a strategy of constructing wavelength-selective actuation of LCE materials by using the SPR photothermal effect can be demonstrated, as done herein. The LCE nanocomposites doped by nanogold or nanosilver were fabricated and exhibited good SPR absorption but in different wavelength bands of the visible spectrum range. They had strong actuation under light irradiation with the wavelengths being inside their respective absorption band but could not be effectively actuated by the light beyond their respective absorption band. A smart electronic device, implementing a hierarchical structured LCE nanocomposite doped by nanogold and nanosilver in different domains as the two-switch actuator, was prepared and capable of outputting different signals in response to the different wavelength bands filtered from a light source, which released the actuator from the restriction of light scanning direction or position. Our work provides new insights for the convenient and precise photoactuation of the LCE actuators.

Photo actuation of liquid crystalline elastomer nanocomposites incorporated with gold nanoparticles based on surface plasmon resonance.

In this work, according to the characteristic of surface plasmon resonance (SPR) of metallic nanoparticles, we investigated the photo actuation performance of a liquid crystalline elastomer (LCE) nanocomposite with incorporated gold nanoparticles (nano-gold/LCE nanocomposite). The nano-gold/LCE nanocomposites were fabricated by incorporating gold nanoparticles into a polysiloxane-based LCE matrix via a novel experimental protocol, and characterized by a well-developed SPR absorption band in the visible spectrum range. The nano-gold/LCE nanocomposites demonstrated strong actuation upon irradiation with a quasi-daylight source; the reason lay in that the SPR response of gold nanoparticles performed efficient energy conversion from light energy to thermal energy, and thus offered an activation pathway for the nematic-isotropic transition of the LCE matrix. The nano-gold/LCE nanocomposites underwent rapid maximum axial contraction up to about one third of the original length under light irradiation, and this photo-stimulated muscle-like actuation was fully reversible via the on-off switching of the light source. The photo actuation properties of nano-gold/LCE nanocomposites with varying irradiation intensities and gold nanoparticle content were also investigated. In addition, the nano-gold/LCE nanocomposites demonstrated superior optical nonlinear properties, and revealed potential for the application area of mode-locking for laser technology.

Photo Actuation Performance of Nanotube Sheet Incorporated Azobenzene Crosslinked Liquid Crystalline Polymer Nanocomposite.

Crosslinked liquid crystalline polymers (CLCPs) containing azobenzene (AZO-CLCPs) are a type of promising material due to their significance in the design of light-driven smart actuators. Developing AZO-CLCP composites by incorporating AZO-CLCPs with other materials is an effective way of enhancing their practicability. Herein, we report an AZO-CLCP/CNT nanocomposite prepared by the in situ polymerization of diacrylates containing azobenzene chromophores on carbon nanotube (CNT) sheets. The liquid crystal phase structure of CLCP matrix was evidenced by the two-dimensional X-ray scattering. The prepared pure AZO-CLCP films and AZO-CLCP/CNT nanocomposite films demonstrated strong reversible photo-triggered deformation under the irradiation of UV light at 366 nm of wavelength, as a result of photo-induced isomerization of azobenzene moieties in the polymer network. But compared to pure AZO-CLCP films, the AZO-CLCP/CNT nanocomposite films could much more rapidly return to their initial shapes after the UV light irradiation was removed due to the elasticity effect of CNT sheets. The deformation behavior of AZO-CLCP/CNT nanocomposite films under the light irradiation was also different from that of the pure AZO-CLCP films due to the interfacial interaction between a polymer network and CNT sheet. Furthermore, incorporation of a CNT sheet remarkably increased the mechanical strength and robustness of the material. We also used this AZO-CLCP/CNT nanocomposite as a microvalve membrane actuator, which can be controlled by light, for a conceptual device of a microfluidic system. The results showed that this AZO-CLCP/CNT nanocomposite may have great potential in smart actuator applications for biological engineering, medical treatment, environment detection and microelectromechanical systems (MEMS), etc.

Photo-Actuation of Liquid Crystalline Elastomer Materials Doped with Visible Absorber Dyes under Quasi-Daylight.

We studied the effect of visible absorber dyes on the photo-actuation performances of liquid crystalline elastomer (LCE) materials under quasi-daylight irradiation. The dye-doped LCE materials were prepared through infiltrating visible absorber dyes into a polysiloxane-based LCE matrix based on its solvent-swollen characteristic. They demonstrated well absorption properties in visible spectrum range and performed strong actuation upon the irradiation from quasi-daylight source, thus indicating that the presence of visible absorber dyes effectively sensitized the LCE materials to light irradiation since the light energy was absorbed by the dyes and then converted into heat to trigger the phase change of LCE matrix. The photo-actuation properties of dye-doped LCE materials with different visible absorber dyes, varied dye contents, and irradiation intensities were investigated. It was shown that the visible absorber dyes with different absorption bands created different photo-actuation performances of LCE materials, the one whose absorption band is near the intensity peak position of quasi-daylight spectrum created the optimum photo-actuation performance. The result disclosed a valuable light utilization way for photo-controlled LCE materials since it revealed that a light-absorbing dye, whose absorption band is in the high intensity region of light spectrum, is capable of effectively utilizing light energy to drive the actuation of LCE materials.