Preparation of Holographic Gratings of Liquid Crystals Dispersed in Polyurethane Acrylates under Controlled Reaction Conditions

Polymers for Advanced Techs

et al. 2008

The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0 < l 31 ) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro-1-butanesulfonyl fluoride) and amounts (0--9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater l 31 gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time.

Section: Materials Oligomer Synthesis and Sample Preparationmentioning

confidence: 99%

Effects of surfactant and molecular weight of polyol on grating formation and switching of holographic PDLC

Shim

Woo

Polymers for Advanced Techs

et al. 2008

“…Thus, an enhanced control of the morphology is paramount to optimize the overall performance of the HPDLC films. [12][13][14][15][16][17] There have been many reports of how to manipulate and improve the electro-optical performance of HPDLC films (e.g., their morphology, diffraction efficiency, switching voltage, speed, and contrast). A major issue concerning HPDLCs is to reduce the driving voltage, which is of importance in practical applications.…”

Section: Introductionmentioning

confidence: 99%

Transmission Holographic Polymer Dispersed Liquid Crystals Based on a Siloxane Polymer

Woo

2008

ChemPhysChem

Self Cite

The low surface energy and the great immiscibility of poly (dimethylsiloxane) (PDMS) with liquid crystals (LCs) are used in the fabrication of holographic polymer dispersed liquid crystals (HPDLCs). By adding increasing amounts of PDMS, the extent of the phase separation between the polymer and the LC, the LC channel width, and-eventually-also the diffraction efficiency of the film can be increased, while keeping the droplet size essentially the same. In addition, the presence of PDMS causes a decrease in the switching voltage and an increase in the response time. At an optimum content of PDMS (PUA40), a minimum switching voltage of 4 V microm(-1), a rise time of 0.20 ms, and a decay of 14.75 ms were obtained. Regarding the effect of the LC content, an overshoot of the diffraction efficiency was observed when the amount of LC exceeded 35 %, which can be attributed to droplet coalescence.

“…HPDLC films operate based on this simple principle. The phase separation can be enhanced by reducing the viscosity of the prepolymer mixture, increasing the solubility parameter gap between matrix and LC and increasing the elasticity of the matrix 4, 5. In particular, phase separation directly related to LC droplet size affects the electro‐optical properties of HPDLC films, which is of practical importance 6, 7.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of electro‐optical properties in holographic polymer‐dispersed liquid crystal films by incorporation of multiwalled carbon nanotubes into a polyurethane acrylate matrix

Lee

Jung

et al. 2010

Polymer International

Self Cite

Holographic polymer-dispersed liquid crystal (HPDLC) films were fabricated with varying amounts of multiwalled carbon nanotubes (MWCNTs) to optimize the electro-optical performance of the HPDLC films. The MWCNTs were well dispersed in the prepolymer mixture up to 0.5 wt%, implying that polyurethane acrylate (PUA) oligomer chains wrap the MWCNTs along their length, resulting in high diffraction efficiency and good phase separation. The hardness and elastic modulus of the polymer matrix were enhanced with increasing amounts of MWCNTs because of the reinforcement effect of the MWCNTs with intrinsically good mechanical properties. The increased elasticity of the PUA matrix and the immiscibility between the matrix and the liquid crystals (LCs) gradually increased the diffraction efficiency of the HPDLC films. However, the diffraction efficiency of HPDLC films with more than 0.05 wt% MWCNTs was reduced, caused by poor phase separation between the matrix and LCs because of the high viscosity of the reactive mixture. HPDLC films showing a low driving voltage (<3 V µm −1 ), a fast response time (<10 ms) and a high diffraction efficiency (>75%) could be obtained with 0.05 wt% MWCNTs at 40 wt% LCs.