Events

 
Joint Seminar - HKUST and SID HK Chapter
Determination of anchoring energy, diamagnetic susceptibility anisotropy and elasticity of some nematics by means of semiempirical method of self-consistent director field

by Prof. Zbigniew Raszewski, Military University of Technology, Poland

Date
 :  06 Apr 2005 (Wed)
Time
 :  3:00pm - 4:00pm
Venue  :  Rm 2407, 2/F (Lift 17-18), HKUST

Abstract
A wedge cell of the wedge angle of order of few mill radians was used to measure threshold electric and magnetic fields for the different kinds of Freedericksz transitions. A nematic liquid crystal filling the cell was of planar orientation enforced by the treatment of the flat boundary plates. A system of interference fringes appeared in the cell placed in normally incident light between analyser and polariser crossed. In the vicinity of each fringe the cell could be considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness; the same relates to any cell of slowly-varying thickness and flat cover plates. The threshold electric and magnetic fields magnitudes were interpreted as the boundary eigenvalue problem for the operator of the second derivative the interaction between the nematics and the substrate was described by the Rapini-Papoular formula (i.e. weak coupling was considered). The resulting formulae were used to determine the polar anchoring energy coefficient and the anisotropy of diamagnetic susceptibility after the threshold fields measured. The method was applied to characterise a few nematic liquid crystals (PCB, 6CHBT, DE) and the coupling between them and the substrates made of some polyimides. The estimates of material parameters agreed pretty well with data taken from literature.


Biography
Graduated from the Department of Chemistry and Technical Physics, Military University of Technology (MUT), Warsaw Poland, in 1973. After graduation, he joined the Institute of Applied Physics, MUT as a Teaching assistant and then lecturer. From 1978 to 1988 he was the Head of the Students General Physics Laboratory MUT, 1988-1994 -Deputy Director of Institute of Applied Physics MUT, 1994-1996 - Head of the Crystal Physics and Technology Department, 1996-1998 - Vice Dean of the Engineering, Chemistry and Technical Physics Faculty. In 1996, he became a professor. Since 1975 he has investigated physics and technology of liquid crystals. He has studied phase transitions of liquid crystals, their optical, elastic and dielectric properties. Among others he intensively studied liquid-crystalline mixtures with induced smectic phases. The main directions of the scientific research nowadays are studies on ferro- and antyferroelectric liquid crystals. He has published over 200 research papers and one book. He has served on several international scientific links and advisory committees connected with liquid crystals.

 

*** All are Welcome ***