Electrically-tunable anomalous electro-optical characteristics of polymer dispersed liquid crystal films

Abstract

The thesis mainly investigates the disorderly and uniformly distributed LC particles in monomers or polymers The size of the LC particles is determinative of their electro-optical (EO) characteristics To methodically and qualitatively explore the peculiar EO characteristics of the LC particles the investigation in this thesis is divided into three parts The first part is to measure the abnormal EO characteristics of polymer-dispersed liquid crystal (PDLC) by applying AC voltage with various frequencies Since the sample will be heated when the frequency of the AC voltage is higher than 10 kHz the second part is to measure the thermal dependent EO characteristics of the PDLC by direct heating The discussion in the first two parts are about the effect of particle size in PDLC on the EO characteristics In the third part the wavelength of the probe beam incident in the PDLC for measurement is varied to realize the relation between the wavelength of the probe beam and the EO characteristics of the PDLC Experimental results show that the Mie scattering theory cannot fully explain the EO characteristics of the large-particle PDLC Therefore the microlens theory is introduced in this thesis Assume the large-particle PDLC as a microlens with a perfectly semispherical shape the lens maker’s formula is adopted to calculate the focal length and then the area ratio of the scattering light and detector is also considered to calculate the transmittance By using this calculation method and the theory of dynamics light scattering by the electrohydrodynamics (EHD) effect in large-particle PDLCs the transmitted features of the large-particle PDLC operated at AC voltage with different frequencies different temperatures or measured by the probe beam with different wavelengths can be completely explained Finally the large-particle PDLC introduced in this thesis is employed to develop tunable light valve devices with lower operating voltage compared to the traditional PDLC Furthermore the light valve device exhibits reversibility and repeatability

Date of Award	2019
Original language	English
Supervisor	Chia-Rong Lee (Supervisor)