| In the modern society,everybody is inseparable from display technology.Currently,liquid crystal displays(LCD)dominate the display technology,and new display technologies represented by organic light emitting semiconductor displays(OLED)are also developing rapidly.The display screen,as the main window for information collection,processing,transmission,and acquisition in modern society,is already an external organ that people can not leave in daily life.After years of development,the display technology in China has accumulated to a certain extent.The raw materials,processing methods,and processing equipment of most of the components in LCD backlight modules have been commercialized domestically,and the research and development of luminescent materials in OLED has also accumulated with a wealth of experience which can be partial commercialized domestically.However,taking the polarizer as an example,the raw materials,processing methods,and processing equipment of the polymer film in the screens are still firmly in the hands of Japanese and South Korean companies.No matter what is the mainstream,LCD displays or advanced OLED displays,polarizer is indispensable.In LCD,the combination of the liquid crystal cell and the polarizer on both sides can determine whether light can pass.In OLED,the combination of polarizer and quarter-wave plate can eliminate the interference of external ambient light on the display.Therefore,the polarizer is a key element that determines the display quality.However,the research on polarizing film processing is no longer fashionable for researchers,and it is difficult to study the structure evolution during the process.The manufacturing of polarizer goes through multiple processing steps,includes multi-scale structural evolutions,and is under multi-field control,which involves multiple scientific problems.In-situ tracking structural evolution during processing can explore the best production parameters.First of all,we establish a high-time-resolved optical path based on quantum cascade laser for in-situ orientation detection.And then,we will introduce that by the means of synchrotron radiation,we try to reveal the role of boric acid in processing;and track the structure evolution of dichromatic substance in PVA during stretch and failure process in this thesis.The main results and conclusions of these work are summarized as follows:(1)A system with the combination of quantum cascade lasers(QCLs)and photoelastic modulator(PEM)has been designed and constructed,which can achieve orientation detection with time resolution of nearly 20 ?s based on the principle of infrared dichroism,several orders of magnitude higher than that of general mid-infrared spectrum.PEM with inherent frequency of 50 kHz is employed to modulate the polarization direction of infrared light rapidly,the controller of which is used to provide the external trigger signal.A double frequency and delay circuit is fabricated to match the frequency of QCLs and PEM as well as overcome the delay during transfer the trigger signal to QCLs controller,which can realize a minimum delay resolution of 5 ns.Also,a data acquisition program is compiled to reduce the data size,making continuous collection possible and lowering difficulty of data processing.The system is combined with a home-made biaxial stretching equipment to conduct the sequential biaxial stretching of ?-polypropylene(PP)film.It shows that the orientation factor of polymer chains increases from 0.04 to 0.36 during machine stretching,which decreases to 0 during transverse stretching,fitting well with the orientation factors estimated with FTIR.The result robustly proves the feasibility of the system for rapid orientation detection.(2)Mechanical and structural evolution of poly(vinyl alcohol)(PVA)induced by uniaxial deformation at different concentrations of boric acid is systematically studied with in-situ synchrotron radiation small-and wide-angle X-ray scattering(SAXS and WAXS).The PVA films were stretched uniaxially in the aqueous solution at room temperature with concentrations of boric acid at 0.3 wt%,1 wt%and 3 wt%,respectively.The stretching process can be divided into three stages through WAXS and SAXS results,whose boundary is the end of the crystallinity platform and the onset of the formation of nanofibrils.In the first stage,the films show elastic stretch with the crystallinity keeping constant and the d-spacing of(101/101)plane(d101/101)decreasing.The unstable crystal breaks up and transfers into amorphous during the second stage so that the force is gradually removed from the unit cell.The connection between the crystal network breaks up in the third stage when the content of boric acid is not enough.Moreover,increasing the concentration of boric acid leads to the earlier emergence of nanofibrils due to the lower energy barrier induced by entropy decrease,which also results in a reduction of nanofibrils content by limiting the mobility of molecular chain.The results have been applied to establish relationships between the microstructure and the physical characteristics of PVA to help us tune the processing parameters during the practical production.(3)The evolution of poly(vinyl alcohol)PVA structure and dichromatic substance induced by uniaxial stretching PVA in the mixed solution with iodine and boric acid(BA)is systematically studied by the combination of in-situ synchrotron radiation small-and wide-angle X-ray scattering(SAXS and WAXD).The experiment is carried out under an orthogonal experimental design for the iodine concentrations of 0.01,0.2,1M,and the BA concentrations of 0.3,1,and 3 wt%,respectively.We divide the stretch process into three regions,whose boundary is the yield point and strain harden point.The PVA-I3-co-crystal generating at high and moderate iodine concentrations is less stable as compared with the PVA crystal,which leads to the earlier decrease of crystallinity at the end of the first region.In the second region,the broken crystal,namely the regular amorphous,is the precursor of the PVA-polyiodide complex.Further increasing the strain,the PVA-I3-co-crystals are generated from the one-dimension polyiodide surrounded by the PVA chains through a melt-reconstruction process.The adequate BA can make it easy to form the polyiodide at the initial state.Still,the increasing rate of polyiodide is suppressed by further added BA due to the limitation of chain movement by the crosslinking agent.In the final region,the emergence of nanofibril can account for the strain hardening of the film.The evolution of polyiodide and PVA-I3-co-crystal revealed by this work gives a better understanding of the polarizer production process,which may guide the resolution of blue leakage of polarizer via an enhancement of the I3-in the crystal form during stretching.(4)The structure evolution of the uniaxially stretched iodized PVA during wetting is systematically studied by the combination of in-situ synchrotron radiation wide-angle X-ray scattering(WAXD)and the homemade stretch machine with humidifying part.The samples with different initial strain and boric acid concentration are applied for the studying of the water stimulate structure evolution.By the means of MDSC,the glass transition temperature(Tg)of the PVA with different water content are measured.It is found that the crystallinity of the films keeps decreasing during wetting.When the crystallinity reaches the minimum value,the stress will generate at the same wetting time.The time will be delay with the boric acid concentration increasing.Meanwhile,the Tg is already far below the room temperature at this time.Our result indicate that the contraction will happen when the crystallinity can not maintain the stability of the films.The boric acid works as the chemical crosslinking agent can replace the crystal to keep the film stable.What's more,the final content of poly iodide will decrease during wetting,which will lead to the polarizer become invalid.This experiment tries to reveal the mechanism of failure of the polarizer during wetting,which may shed some light on the manufacturing of the durable polarizer. |
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