| Polymer optical films are one of the indispensable components in display panels,have played as an extremely important role in this image displaying age. For instance,polarizers used in liquid crystal display (LCD) are composited by multiple layers of polymer optical films. Poly (vinyl alcohol) (PVA) films can be stretched to form the structure of nanofibrils and the complex of PVA-1 in KI/I2 solutions, are particular suitable for being the substrate materials of polarizers. However, there are some challenges to study the manufacturing of PVA films from the perspective of basic film processing physics. One is that the manufacturing of PVA films is a continuous process mainly contains swelling, iodine-staining, washing, stretching and drying, which is coupled and influenced by multi procedures and parameters. The other is the high demand of constructing the film processing apparatuses on laboratory level, as well as when combining with complicated in-situ measurements.Considering the problems above, we have designed the uniaxial stretching machine in solutions to follow the structure evolution of PVA films drawn in KI/I2 solution. Analyzing these results helps us to deeply understand its manufacturing production principles, has provided valuable guidance for choosing the strain and concentration to obtain the best property of PVA films. Major research works and conclusions are as follows:(1) Developed the in-situ film blowing systems combined with infrared temperature testing and synchrotron radiation SAXS/WAXS measurements. Two homemade auto-lifters were constructed and holding the 200 kg weight blown machine move up and down with a slow speed of 0.05 mm/s. By redesigning the air ring,structure information of film bubble could be obtained as soon as it came from the die.(2) Constructed the uniaxial stretching machine in solutions which was driven by high-precision servo motors, two sides of clamps were reverse shifting using two linear sliders. The spacing between incident and scattering holes in the sink was 3 mm,ensuring the attenuation of X-ray was acceptable and the samples was away with the inside of sink. Servo motors could keep the clamps moving precisely under the slow speed of 0.2 mm/s. The tension sensor could record the mechanical information of films when stretching. The electric hearing plates and proportion integration differentiation were empolyed to keep the homogeneous environment temperature without overshoot.(3) The fibrillation and complexation reaction between PVA-I complexes are studied with in situ synchrotron radiation small- and wide-angle X-ray scattering(SAXS/WAXS) during uniaxial stretching PVA film in KI/I2 aqueous solution. SAXS results show that stretch induces the formation of nanofibrils, which pack periodically with an average inter-nanofibrillar distance around 10 nm in the later stage of stretch.The onset strains for fibrillation and the appearance of periodicity of nanofibrils locate at the beginning and the end of stress plateau, which decrease with the increase of iodine concentration. The presence of iodine ions reduces the crystallinity of PVA crystal but favors the formation of PVA-I complex in the whole stretching process. The complexation reaction is promoted by the synergistic effect of stretch and iodine ions,during which stretch drives the formation of polyiodine via the effect of entropic reduction while iodine concentration dictates crystallization of PVA-I3- co-crystal through the role of chemical potential. A morphological and structural phase diagram is constructed in strain-iodine concentration space, which defines the regions for fibrillation and complexation reactions and may serve as a roadmap for industrial processing of PVA polarizer. |
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