The Electro-Optical Properties and Adhesion Strength of Epoxy-Polymercaptan-Based Polymer Dispersed Liquid Crystal Films

Polymer dispersed liquid crystal (PDLC) films were prepared by thermal polymerization-induced phase separation in epoxy/polymercaptan/liquid crystal (LC)/accelerator mixtures. The effects of the concentration of LC and accelerator, the curing temperature, and the structure of epoxy monomer on the electro-optical (E-O) properties and adhesion strength of the PDLC films were studied systematically via E-O, peel strength, DSC, IR, and gel measurements. It showed that different polymer structures and the properties of the polymer can be obtained by changing the compositions and the curing temperature, which had significant impacts on the E-O properties of the PDLC films. Meanwhile, the polymer matrix with high glass-transition temperature (Tg) and small pore size will improve the adhesion strength of the PDLC film, and these kinds of epoxy-polymercaptan-based PDLC films have better performance than traditional acrylate-based PDLC in the aspect of the adhesion strength. This work may provide some inspiration in preparing epoxy-polymercaptan-based PDLC films, which both have excellent E-O performance and good adhesion strength, towards roll-to-roll processes and large-scale flexible applications.

Intrinsically Visible Light-Responsive Liquid Crystalline Physical Gels Driven by a Halogen Bond

Photoresponsive physical gels using liquid crystals (LCs) as solvents have attracted great interest owing to their potential applications. But, current investigations mainly focus on UV light, which is not environment-friendly enough. On the other hand, the halogen bond is a novel tool for constructing supramolecular gels because of good hydrophobicity, high directionality, tunable strength, and large size of halogen atoms. Herein, to construct an LC physical gel with both the advantages of a halogen bond and visible light response, azopyridine-containing Azopy-C₁₀ is chosen as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene is selected both as the halogen bond donor and for the intrinsically visible light response. Such a binary gelator can self-assemble in the anisotropic solvent of nematic LC 5CB to form an LC physical gel. It experiences the gel-to-sol transition by green light irradiation. As the gelator concentration increases, the saturation voltage increases, but the switch-off time decreases. The combination of the halogen bond and controllable visible light-responsive LC physical gel provides the feasibilities of manipulating these smart soft materials.

Acrylate-assisted fractal nanostructured polymer dispersed liquid crystal droplet based vibrant colored smart-windows

We have studied liquid crystals (LCs) and acrylate-assisted thiol–ene compositions to synthesize dye based colorful polymer dispersed liquid crystals (PDLCs) without using a photo-initiator for smart-windows applications. A typical PDLC mixture was prepared by mixing LCs with UV-curable monomers, which included triethylene glycol diacrylate (TEGDA), trimethylolpropane diallyl ether (TMPDE, di-functional ene monomer), trimethylolpropane tris(3-mercaptopropionate) (TMPTMP, a thiol as a cross-linker), and a dichroic dye. The ratios of the TMPDE/TMPTMP and the LCs/TEGDA showed significant effects in altering the properties of the UV-cured PDLCs. During the curing process, the monomers polymerize and led to the encapsulation of the LCs in the form of interesting fractal nanostructures by a polymerization induced phase separation process. The switching time, electro-optical properties, power consumption, and ageing of the fabricated PDLCs were investigated. It was possible to achieve a 70–80% contrast (ΔT) at a voltage difference of ∼70 V with a fast switching time (τ) as low as < 20 milliseconds (ms) and low power consumption. These PDLCs had a low threshold voltage that ranged between 10 and 20 V. The sustainability of the fabricated UV-cured PDLCs was analyzed for up to 90 days, and the PDLCs were observed to be stable.

Vibrant colored smart-windows were fabricated based on acrylate-assisted fractal nanostructured polymer dispersed liquid crystals.

Photomodulated Electro-optical Response in Self-Supporting Liquid Crystalline Physical Gels

Photoresponsive liquid crystal (LC) physical gels have attracted more and more attention because of the nature of strong response via light stimulus. Although many efforts on the breaking and recovering of physical gels through photoisomerization have been focused, fast electro-optical response and high mechanical properties even upon light irradiations are difficult to achieve at the same time. In this work, two kinds of azobenzene-containing gelators (AG1 and AG2) with different terminal groups were designed and synthesized. Both gelators could induce the nematic LC P0616A self-assemble into anisotropic phase-separated LC physical gels at low contents. Their phase-transition behavior, thermal stability, microstructure, and mechanical strength were systematically studied. Compared with AG2 in P0616A, the P0616A/AG1 gels showed better mechanical property. When the gelator content was above 3 wt %, the P0616A/AG1 gels possessed good self-supporting ability with a storage modulus more than 10⁴ Pa. Thus, the photoresponsive electro-optical properties and structures of P0616A/AG1 gels were focused in detail. It was surprising that the electro-optical response speed of the P0616A/AG1 gels could be promoted upon UV irradiation. In particular, the decay time (τ_off) was only about half when compared with the initial state, whereas the gels still exhibited good self-supporting ability; also the network of the LC physical gels had no change at macro- and microstructural levels. These exciting results would open a door for the application of this material in electro-optical devices.

A novel light diffuser based on the combined morphology of polymer networks and polymer balls in a polymer dispersed liquid crystals film

A novel light diffuser based on a thermally cured polymer dispersed liquid crystal film was made by thermally curing epoxy monomers with thiols and polyamine in a solution of monomers and liquid crystals between two transparent polyethylene terephthalates.

Low power consumption and high-contrast light scattering based on polymer-dispersed liquid crystals doped with silver-coated polystyrene microspheres

Polymer-dispersed liquid crystals (PDLCs) have attracted considerable attention for optical device applications in recent years. However, the high operating voltage of PDLCs limits their applications. This study reports a simple approach used for the first time to decrease the operating voltage of PDLCs by means of doping 3 μm-diameter silver-coated polystyrene microspheres (Ag-coated PSMSs) into PDLCs. Ag-coated PSMSs construct an induced electric field between each other when an external electric field is applied. This induced electric field can enhance the effective electric field so the operating voltage can be actively reduced from 77 V to 40 V. Such PDLCs also possess a high contrast ratio of >50 and a high on-state transmittance of ~73%. Therefore, PDLCs doped with Ag-coated PSMSs maintain a high contrast ratio and improve their electro-optical properties.

Monodisperse PDLC composites generated by use of polyvinyl alcohol boric acid as matrix

PDLC composites with narrow size polydispersity and radial droplet configuration were obtained using polyvinyl alcohol boric acid as carrying matrix.