Fabrication And Research Of Polymer Dispersed Liquid Crystal Films

Manufacture of parts made by liquid crystal is very important in electronic and communicate industry. Because of advantages such as lower working volt and energy consumer, higher resolution, no harmful radiate and smaller volume, these parts are used in the manufactures of electronic watcher, computer, mobile phone, et al. Twisted and super twisted nematic liquid crystal parts are used as display by combination of electronic-photo effect and integrate circuit traditionally. Advanced parts such as nematic, polymer disperse, double or multiple stable, ferroelectric, and anti-ferroelectric liquid crystal are made now. Especially polymer disperse liquid crystal (PDLC) is highly potential as composite material. PDLC could be used more wildly in application as display with soft and big area, photoelectric swatch and grating due to advantages such as without polar and orientation meter, simpler manufacture process compared with traditional liquid crystal parts.The fabrication of the PDLC film is mainly made by polymerization induced phase separation of the mixture. In such as a process the monomer and liquid crystal is mixed as a homogenous solution and initiated by polymerization to increase monomer's molecular weight. When the monomer's molecular weight is close to critical point, the solubility between monomer and liquid crystal is decreased and phase separation occur. Liquid crystal droplets are formed and the size of the droplets increased gradually. Finally the shape of the droplets is fixed by the polymer. Under this process the polymeric temperature is higher than that of clear point and the solubility between monomer and liquid crystal is high, which result in more liquid residue exists in the polymer phase and more monomer residue exists in liquid phase. The photoelectric properties of PDLC are severely affected by this problem. Irregular shape and low degree of conversion of the PDLC film are also disadvantages.The two kinds of PDLC films, acrylates such as Bis-EMA2,Bis-EMA4,Bis-EMA15, and thiol monomer NOA65 dispersed liquid crystal films are made by first application of an alternating current promoted phase separation process. The disadvantages such as irregular shape and high residue were overcome by this method. The polymerization rate is increased by application of high intensity visible light, in which the harmful effects caused by UV light are avoided. The main works in this paper are as following:1. Effects affected phase and kinetic behaviors of acrylates(Bis-EMA2,Bis-EMA4,Bis-EMA15)/LC and thiol (NOA65)/LC systems were carefully studied, the results are as following:(a) The clear points of acrylates(Bis-EMA2,Bis-EMA4,Bis-EMA15)/LC and thiol (NOA65)/LC systems decrease with the decrease of LC concentration. The UCST of the systems become higher after polymerization.(b) The phase separation process could be divided into three stages for all the systems : LC phase transition stage; LC droplets fast growth stage; hypercoalescence. The depression of transition and combination occurred at different extent with decrease of diameter and amount increase of the droplets when the concentration of LC decreased in all systems. Hypercoalescence was stopped when the concentration of LC was lower to 80% in Bis-EMA2/LC,Bis-EA4/LC,NOA65/LC system and 60% in Bis-EMA15/LC system.(c) The depression of transition and combination also occurred with increase of phase separation. When temperature was increased to 35℃the hypercoalescence stopped for NOA65/LC system, 40℃for Bis-EMA2/LC,Bis-EA4/LC systems. Hypercoalescence still occurred with Bis-EMA15/LC system but the diameter of the droplets obviously decreased with increase of temperature.(d) Beside concentration and temperature, the degree of phase separation was also connected with structure of monomers. The solubility of LC with acrylates Bis-EMA2,Bis-BIS-EA4,Bis-EMA15,decreased with increase of hydrocarbon chain.(e) The transition and combination was affected by application of alternating current for all systems with phenomena such as decrease and more homogenous distribution of diameter of the droplets, shorter time to reach phase equilibrium.2,Phase separation automatically happened when the temperature was lower than clear point (TNI) for all the systems. The distribution of droplet size was wider and distance between droplets was longer. The droplets, on the other hand, were with small size distribution and homogenous shape under alternating current existence. In order to obtain ideal droplet shape, different electric potentials were required for different system; 6V/μm for acrylates/LC and 3V/μm for thiol/LC system. The ideal shape obtain under AC existence could be kept by fast polymerization. The polymerization times are 25s for Bis-EMA2//LC, Bis-EA4//LC, 40s for Bis-EMA15//LC and 50s for NOA65/LC separately. The size, shape and arrangement of the droplets are not affected by fast polymerization. The polymer is more tight, the thickness of the polymer wall is more homogenous and smooth, which lowered the LC residue in polymer and resulted in a decrease of anchoring energy between polymer and LC.3,The Bis-EMA2, Bis-EA4, Bis-EMA15, NOA65 dispersed in P0616A films were fabricated separately with an alternating current promoted phase separation process and without this process. Orientation parameters of LC molecules in these films were measured and calculated by polarized IR spectroscopy. The results shown that under non-working condition (without applied electric field) all the orientation parameters were low, the values of orientation parameters related to rigid part were a few higher than those of fat chain. All the parameters of LC molecules under working condition were much bigger than those of same LC molecules under non working condition. The parameters related to LC molecules in the films that were fabricated with n alternating current promoted phase separation process were higher than those of LC molecules without such a process, which indicated that orientation along electric field of former molecules is more ordered than that of the latter and anchoring energy was lowered by introduce of an alternating current promoted phase separation process. The changes of orientation parameters were bigger and the orientation along electric field occurred more easily for the LC molecules in the films fabricated with the process.In summery, the research of present study lines not only in the further investigation and broadening on the polymerization induced phase separation (PIPS),but also in the more embedded comprehension of the traditional PIPS technique and the fabrication processing of PDLC films as well as the correlation theories .At the same time ,it provides the referencable ideas for the studies of PDLC. Phase separation under alternating current electric field techniques given by the research will provide a new way to fabricate PDLC films.