Effects of Temperature on the Alignment and Electrooptical Responses of a Nematic Nanoscale Liquid Crystalline Film

Abstract

The surface-induced alignment and electrooptical (EO) dynamics of a 50-nm-thick liquid crystalline (4-n-pentyl-4'-cyanobiphenyl; 5CB) film were studied at three temperatures: 25 and 33 degrees C (near the crystalline-nematic and nematic-isotropic transition temperatures, respectively) and 29 degrees C (a median temperature in the stability region of the nematic phase). The ZnSe surfaces that entrap the liquid crystal (LC) film have been polished unidirectionally to produce a grooved surface presenting nanometer-scale corrugations, a structure that induces a planar and homogeneous orientation in the nematic phase. The present work attempts to understand the influences of temperature on the surface-induced alignment and corresponding EO dynamics of the material. Step-scan time-resolved spectroscopy measurements were made to determine the rate constants for the electric-field-induced orientation and thermal relaxation of the 5CB film. The field-driven orientation rates vary sensitively with temperature across a range that spans the stability limits of the nematic phase; the relaxation rates, however, vary very little across this same temperature range. We propose that these differences in LC behavior arise as consequence of the interplay of the temperature dependence of the elastic constants, viscosity, and degree of orientational order of the LC medium. A simple theoretical model provides some understanding of these behaviors.

Exploitation of orientation of liquid crystals 5CB and DSCG near surfaces to detect low protein concentration

“…Pattanayek vibration mode of a chemical group is associated with a characteristic peak in the spectra. The observed peaks for pure 5CB are comparable to those of the reported values [21][22][23][24][25][26]. Notable peak positions corresponding to the vibration mode of a group are as follows: phenyl C-H in-plane deformation at 1185 cm −1 , pentyl C-H stretching at 1466 cm −1 and 1397 cm −1 and C-N stretching at 2226 cm −1 .…”

Self-Assembly of Chemically Linked Rod−Disc Mesogenic Liquid Crystals

“…The combination of order and mobility in these soft materials leads to novel functional properties useful in electro-optical applications and in the field of life science. [2][3][4][5][6][7][8][9] Both the mesogenic groups and the flexible tails can be designed to tune important LC properties. [10][11][12] Standard mesogens are either rod or disc shaped, while methylene or ethylene oxide segments are often used as flexible tails.…”

“…In this publication, we demonstrate the construction of newly designed molecular discs. This series of new molecular discs (RDn, here n is the number of carbon atoms between rod and disc mesogens) has been synthesized via the chemical linking of each of six cyanobiphenyl rod mesogens (R) to the triphenyl disc-like mesogenic group (D) by means of alkyl chains (n ) [6][7][8][9][10][11][12]. In this study, the RD12 compound with 12 carbon atoms in each of the alkyl chain linkages between the rod and the disc mesogens is used to represent the phase structures and transition behavior of this newly synthesized series.…”

“…The long-range order in LC phases is partly lost due to the mobility of the constituent building blocks. The combination of order and mobility in these soft materials leads to novel functional properties useful in electro-optical applications and in the field of life science. − …”