Polymer Dispersed Liquid Crystal (PDLC)
Fluid Physics: Fluid and interface physics
Convection and Segregation in Crystal Growth
Drop Tower Bremen - DYT2009
J.C. Leitao (1), M. Matos (1), R. André (1), R. Zambujal (1), C. Rosa (1), P. Simeao (1)
|(1)||University of Porto (FCUP)|
Faculty of Sciences
Department of Physics and Astronomy
Rua do Campo Alegre, s/n
A study on Polymer Dispersed Liquid Crystal (PDLC) materials obtained from polymerizations in 0g and 1g with three different liquid crystals (LCs) was made. Physical and structural properties such as size and shape of LC droplets, light transmission, reorientation field, response time and hysteresis effects, that are very important for electro-optical applications of PDLCs, are being studied for various polymer:LC ratios, liquid crystals, and gravity acceleration during polimerization. Spatially varied droplet size samples were also produced – through the variation of UV-light intensity when polymerizing – and are being studied.
The aim of this project is to study the influence of microgravity on PDLC properties in order to develop materials and techniques that will allow smaller LC reorientation fields, increased optical transmission and contrast, and reduced hysteresis. Preliminary results point to an improvement on PDLC optical transmission and contrast characteristics, with an increase in contrast of 6,8%.
All the samples were prepared at FCUP before going to Bremen. To prepare them, each LC was mixed with the NOA-81 photo-polymer with the desired mass ratio; the mixture was then homogenized in an ultrasound wave chamber for about 30 minutes and then put inside the cells. The samples were handled with care to avoid exposure to UV-light.
At ZARM Drop Tower, the setup was integrated in the drop capsule and the drops were made under controlled temperature and pressure. All the samples were polymerized during ~9s with different light intensities according to the polymer:LC ratio of each sample. The light intensities were chosen from preliminary tests performed at FCUP in order to guarantee the pre-cure of the polymer. Finally, the full polymerization, with UV exposures of 5min duration, was made back at the faculty under normal gravity conditions with the same light intensity that was used in microgravity.
Please find results in the final report attached to this experiment record.
|Fig. 1 Aluminium plates.|
|Fig. 2 Checking the Aluminium plates.|
|Fig. 3 Experimental setup attached to the drop capsule.|
|Fig. 4 Last preparations of experimental setup attached to the drop capsule.|
|Fig. 5 Experiment integrated in the drop capsule.|
Natacha Callens (e-mail: firstname.lastname@example.org)