Yanzi Gao

A novel soft matter composite material for energy-saving smart windows: from preparation to device application

Nowadays, with the increasing energy consumption of buildings and the continuous improvement of human living standards, use of architectural glass with multi-functional features of large-scale manufacturing, safety and energy saving has become the mainstream trend. In this paper, a series of cholesteric side-chain liquid crystal polymers (ChSCLCPs) are designed and synthesized to composite with a widely used laminating material for safety glasses, ethylene-vinyl acetate (EVA), to endow the windows with IR light shielding property. The synthesized ChSCLCPs have the desired reflection wavelengths and thermal stability. Preparation methods of EVA/ChSCLCP composite materials are investigated and different ratios of the contents and various film treatment conditions are attempted. Interestingly, when the contents of EVA and ChSCLCP are equal, “sky-blue” areas are found under polarized optical microscopy (POM) and the film exhibits stronger light scattering and selective reflection properties. Taking advantages of this phenomenon, a new type of IR shielding film is manufactured by the powder blending method and it not only performs broadband reflection, but also exhibits a strong light scattering. Then, model buildings equipped with and without the film are set up and an energy conservation efficiency of up to 40.4% is obtained, which proves the films practical applications in energy-saving smart windows.

Studies on the electro-optical and the light-scattering properties of PDLC films with the size gradient of the LC droplets

Polymer dispersed liquid crystal (PDLC) films with the size gradient of the LC droplets were prepared based on the epoxy/acrylate hybrid polymer matrix. The ultraviolet (UV) intensity gradient was induced by the UV-absorbing dye over the thickness of the samples. Taking advantage of the difference between the epoxy monomers and acrylate monomers in polymerisation rates and the UV intensity gradient, the gradient distribution of the LC droplet size was formed in PDLC films. The effect of the size gradient of the LC droplets on the electro-optical and the light-scattering properties of PDLC films was investigated. The results showed that due to the size gradient distribution of the LC droplets, PDLC films could exhibit the strong light scattering in the UV-visible-near infrared (VIS-NIR) region. Consequently, it provides a potential approach for modulating NIR light transmittance.

Synthesis and self-assembly behaviours of side-chain smectic thiol–ene polymers based on the polysiloxane backbone

A series of polysiloxane side chain liquid crystal polymers (PSCLCPs) with chiral and achiral substitutions in the side chains, denoted as PMMS-Xchol-n (n = 0, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5 0.6, 0.7. 0.8, 0.9, and 1.0, respectively, the molar content of the chiral cholesteric unit (Xchol) in a specific polymer), were successfully synthesized via thiol–ene click chemistry. The molecular structures of the polymers were confirmed by 1H-NMR, FT-IR, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). Their liquid crystalline (LC) properties and self-assembling behaviors were investigated in detail by a combination of various techniques, such as differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction. The results demonstrated that the phase transition behaviour and the self-assembly structure of the polymers were significantly influenced by Xchol and temperatures. With increased Xchol, the clearing points increased significantly, their mesogenic temperature ranges greatly widened, and abundant mesophases developed. Generally, two different types of LC phase structures and three different molecular arrangements were observed, depending on the two LC building blocks. Polymers with Xchol below 0.3 could self-assemble into a smectic E (SmE)-like structure and a single layer smectic A (SmAs) structure upon heating. When Xchol was between 0.4 and 0.7, a single phase structure of a SmAs or a bilayer smectic A (SmAd) could be observed. While for polymers with Xchol over 0.8, a SmAd phase structure was self-organized, further heating led to a SmAs structure. Moreover, when the molar ratio of the chiral group or achiral group was about 0.1, a microphase-separated smectic morphology could be found, indicating that the introduction of a small amount of any components in the copolymers might destroy the well-ordered structures.

Stimuli-Directed Dynamic Reconfiguration in Self-Organized Helical Superstructures Enabled by Chemical Kinetics of Chiral Molecular Motors

Abstract Dynamic controllability of self‐organized helical superstructures in spatial dimensions is a key step to promote bottom‐up artificial nanoarchitectures and functional devices for diverse applications in a variety of areas. Here, a light‐driven chiral overcrowded alkene molecular motor with rod‐like substituent is designed and synthesized, and its thermal isomerization reaction exhibits an increasing structural entropy effect on chemical kinetic analysis in anisotropic achiral liquid crystal host than that in isotropic organic liquid. Interestingly, the stimuli‐directed angular orientation motion of helical axes in the self‐organized helical superstructures doped with the chiral motors enables the dynamic reconfiguration between the planar (thermostationary) and focal conic (photostationary) states. The reversible micromorphology deformation processes are compatible with the free energy fluctuation of self‐organized helical superstructures and the chemical kinetics of chiral motors under different conditions. Furthermore, stimuli‐directed reversible nonmechanical beam steering is achieved in dynamic hidden periodic photopatterns with reconfigurable attributes prerecorded with a corresponding photomask and photoinduced polymerization.

Influence of shorter backbone and cholesteric monomer percentage on the phase structures and thermal-optical properties of linear siloxane tetramers containing cholesterol and benzene methyl ether groups

A series of new linear polysiloxane tetramers containing cholesterol and benzene methyl ether groups as side chains was successfully synthesized via a typical hydrosilylation reaction. Their chemical structures were confirmed by 1H-NMR, FT-IR and thermogravimetric analysis (TGA). A combination of analysis methods such as differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction was carried out to systematically investigate their phase transition behaviours and phase structures. The results revealed that the mesophase structures of all the polymers were greatly dependent on the molar content of the chiral cholesteric unit (Xchol). Polymers with Xchol below 0.60 or over 0.70 could develop a stable cholesteric phase or smectic A phase, while both smectic A and cholesteric phases could be formed for polymers with Xchol between 0.60 and 0.70. Besides, polymers with Xchol below 0.60, which developed a cholesteric phase with sufficiently wide temperature ranges in the entire mesomorphic state (minimum over 50 °C and maximum over 130 °C), could also exhibit tunable selective reflection wavelengths between 470–560 nm upon heating and arbitrarily regulated glass transition temperatures between 0–40 °C. As a result, a thermochromism liquid crystalline material for temperature sensors was successfully obtained. Surprisingly, different from the results previously reported, an unusual phenomenon of the centre selective light reflection wavelength (λm) vs. Xchol, which decreased dramatically (blue shift) at first, then had a remarkable red shift with increasing Xchol, was first observed.

A Study on the Electro-Optical Properties of Thiol-Ene Polymer Dispersed Cholesteric Liquid Crystal (PDChLC) Films

In this study, a polymer dispersed cholesteric liquid crystal (PDChLC) film obtained via a one-step fabrication technique based on photopolymerization of a thiol-acrylate reaction system was prepared and characterized for the first time. The effects of the chiral dopant, the influence of thiol monomer functionality and content on the morphology and subsequent performance of the PDChLC films were systematically investigated. It was demonstrated that the addition of a small amount of chiral dopant slightly increased the driving voltage, but decreased the off-state transmittance significantly. Furthermore, scanning electron micrographs (SEM) shown that the liquid crystal (LC) droplet size decreased at first and then increased with the increasing amount of thiol monomer functionality, while increasing the thiol content increased the LC droplet size. Correspondingly, the electro-optical switching behavior was directly dependent on LC droplet size. By tuning the raw material composition, PDChLC film with optimized electro-optical performance was prepared.

Effect of a Polymercaptan Material on the Electro-Optical Properties of Polymer-Dispersed Liquid Crystal Films

Polymer-dispersed liquid crystal (PDLC) films were prepared by the ultraviolet-light-induced polymerization of photopolymerizable monomers in nematic liquid crystal/chiral dopant/thiol-acrylate reaction monomer composites. The effects of the chiral dopant and crosslinking agents on the electro-optical properties of the PDLC films were systematically investigate. While added the chiral dopant S811 into the PDLC films, the initial off-state transmittance of the films was decreased. It was found that the weight ratio among acrylate monomers, thiol monomer PETMP and the polymercaptan Capcure 3-800 showed great influence on the properties of the fabricated PDLC films because of the existence of competition between thiol-acrylate reaction and acrylate monomer polymerization reaction. While adding polymercaptans curing agent Capcure 3-800 with appropriate concentration into the PDLC system, lower driven voltage and higher contrast ratio were achieved. This made the polymer network and electro-optical properties of the PDLC films easily tunable by the introduction of the thiol monomers.

Polysiloxane-Based Side Chain Liquid Crystal Polymers: From Synthesis to Structure–Phase Transition Behavior Relationships

Organosilicon polymer materials play an important role in certain applications due to characteristics of much lower glass transition temperatures (Tg), viscosities, surface energy, as well as good mechanical, thermal stabilities, and insulation performance stemming from the higher bond energy and the larger bond angles of the adjacent silicon-oxygen bond. This critical review highlights developments in the synthesis, structure, and phase transition behaviors of polysiloxane-based side chain liquid crystal polymers (PSCLCPs) of linear and cyclic polysiloxanes containing homopolymers and copolymers. Detailed synthetic strategies are elaborated, and the relationship between molecular structures and liquid crystalline phase transition behaviors is systematically discussed, providing theoretical guidance on the molecular design of the materials.

Angular Photochromic LC Composite Film for an Anti-Counterfeiting Label

In the harsh application environment, improving the mechanical properties of liquid crystal materials is a fundamental and important problem in the design of anti-counterfeit materials. In this paper, by a stepwise polymerization of first, photo-polymerization and subsequently thermal-polymerization, a coexistent polymer dispersed network was first constructed in cholesteric liquid crystal materials containing a photo-polymerizable system of urethane acrylate and a thermo-polymerizable system of isocyanate. Results revealed that the coexistent polymer dispersed network exhibited largely enhanced mechanical performance, and the networks obtained by different methods had different contributions to the enhancement of the peel strength and toughness of the composite films. Then an angular photochromic anti-fake label based on a coexistent polymer dispersed network with enhanced mechanical and apparent angular discoloration characteristics, suitable for practical applications, was successfully achieved.

Preparation of polymer-dispersed liquid crystal doped with indium tin oxide nanoparticles

ABSTRACT To study polymer-dispersed liquid crystal (PDLC) films doped with indium tin oxide (ITO) nanoparticles (NPs), samples were prepared by ultraviolet-initiated polymerisation based on the thiol–acrylate system. Owing to the interaction between PDLC system and ITO NPs, the content and the size of ITO NPs are the main determinants to the microstructure which plays an essential role on the electro-optical and anti-infrared properties of the PDLC films. In the polymer matrix, a novel microstructure consisting of a dense surface, micron-sized meshes and submicron meshes is found to benefit the better performances of the low driven voltage (20.7 V), the relatively high contrast ratio (8.3) and the lowest transmittance(500–2500 nm) on average at about 3.55% with maximum of merely 7.6%. Thus, it lays a solid foundation for the further investigations on the microstructure and the performance of the PDLC films. Meanwhile, it is proved that the PDLC film, improved performance through doping ITO NPs, is promising to be a superior choice in the field of energy-saving. Graphical Abstract