Research On Polymer Stabilized Nematic Liquid Crystals Smart Windows And Its Characteristics Based On Flexible Substrate

Polymer stabilized nematic liquid crystal(PSNLC)smart windows switch from the transparent state comparable to normal glasses to the strong scattering state when powered on,which is ideal for the regulation of sun light.PSNLC smart windows can be applied to offices,residences,greenhouses and other buildings that need their windows to stay transparent for a long time.It has a broad market prospect and conforms to the development direction of energy-saving,environmentally friendly,low-carbon and low-energy buildings.However,the current PSNLCs all use glass as the substrates and lack mechanical strength,which cannot be easily adapted to the curved or specially shaped windows.Moreover,the original windows need to be removed during installation,which will cause a great waste of resources.Therefore,it is of great significance in terms of both scientific research and market value to studying how to realize flexible PSNLC smart films based on material design and device structure engineering while maintaining the excellent electro-optic performance of current PSNLC is of great significance in terms of both scientific research and market value.This thesis starts from exploring the preparation method of the homeotropic alignment layer that is compatible with flexible substrates,and further introduces functional groups to modify the alignment layer to enhance the adhesion between the interface and the polymer network of PSNLC.In addition,the strength of the polymer network can be enhanced by increasing the concentration of polymerizable liquid crystal(LC)monomers.The introduction of a reversible addition-fragmentation chain transfer(RAFT)agent can further regulate the structure of polymer network and adjust the electro-optic properties of PSNLC.Finally,a PSNLC smart film is successfully prepared on a flexible substrate and its potential applications are explored.The main research contents are as follows:(1)Research on the effect of imidization temperature on the alignment layer and the performance of PSNLC.The homeotropic alignment effect of the alignment layer obtained by curing polyamide acid(PAA)film at different temperatures and the influence on the electro-optic properties of PSNLC are discussed.The results show that when the PAA film is partially imidized at 150 °C,the long alkyl group in the molecule can effectively stretch away from the substrate,thus inducing the homeotropic alignment of the LC molecules without any obvious defect.After the PSNLC is formed after photopolymerization,the incompletely imidized PAA film will not affect the electro-optic performance of PSNLC since the homeotropic alignment layer has a weaker binding ability towards the LC molecules than the polymer network.In this way,the preparation of homeotropic alignment layer on the flexible substrate can be realized.(2)Research on the preparation of homeotropic alignment layer by a one-step method using silane and application to PSNLC.The preparation method of alignment layer based on long-chain silane and mixed silane is studied,as well as the effect on the performance of PSNLC when the one-step method is applied.The results show that under suitable one-step preparation conditions,the methoxy group of the long-chain silane reacts and is grafted onto the substrate through covalent bonding.The long alky group can effectively induce the homeotropic alignment of the LC molecules.Furthermore,incorporating a short-chain silane of a suitable concentration will not disrupt the effect of homeotropic alignment.The methacrylate functional group of the short-chain silane can participate in the radical polymerization by forming a covalent bond with the polymer network.The connection improves the adhesion between the polymer network and the interface without affecting negatively the electro-optic properties of PSNLC.(3)Research on the effect of RAFT chain transfer agent(CTA)on PSNLC polymer network and performance.The effect of CTA,LC monomer and photoinitiator concentration on the polymer structure and the electro-optic properties of PSNLC are studied.The results show that the addition of RAFT chain transfer agent can effectively control the polymerization reaction kinetics and the formation of polymer network structure,therefore breaking the trade-off between the strength of the polymer network and the electro-optic properties of PSNLC.When the mass ratio of negative LC,LC monomer,photo-initiator and CTA is 91.5:8.0:0.2:0.3,the strength of the polymer network of PSNLC is doubled compared to the traditional material system.The PSNLC of the new material system keeps excellent electro-optic properties and can continuously regulate light in the wavelength range of 400-1350 nm.(4)The characteristics and application of PSNLC based on flexible substrate.The electro-optic properties and power consumption of PDLC film and PSNLC film are compared,and the characteristics of PSNLC film are studied using light scattering theory.The results have shown that the power consumption of the PSNLC film is only half of that of the PDLC film.Meanwhile the working voltage is within the safe voltage range for human body.According to the theory of Rayleigh and Mie scattering,PSNLC film can scatter both the visible and infrared light.The ability of forward scattering is stronger than the backward scattering.When the PSNLC film is used in buildings,the forward scattering can ensure that part of the light enters the room and provide a certain luminous flux.On the other hand,the backward scattering can block part of the visible and infrared light from entering.The backward scattering of infrared light can help reduce the indoor temperature.