Surface electroclinic effect on the layer structure of a ferroelectric liquid crystal

Abstract

Optical second-harmonic generation and ellipsometry were used to study molecular alignment in an interfacial region and the deviation of the layer normal from the surface-rubbing axis in the smectic-/4 phase of a ferroelectric liquid crystal. The results can be well explained by the surface electroclinic effect. PACS numbers: 6l.30.Gd, 42.65.Ky, 64.70.Md, 68.45.-v The problems of interfacial properties of liquid crystals (LCs) are not only of fundamental interest but also of practical importance to the design and construction of LC devices. It is well known that an LC film can be oriented by a rubbed polymer surface [1]. It has been recently shown that the rubbed polymer surface effectively aligns the first LC monolayer on the surface, and then via LC molecule-molecule interaction, the average molecular orientation (the director) in the bulk is aligned [2,3]. Recently, however, it has been found that in the smectic-/^ iSmA) phase of chiral molecules the bulk LC director and hence the smectic layer normal deviate from the rubbing axis by an angle 0, which can be as large as 18° [4,5]. Nakagawa et ai [4] observed that the sign of 0 correlates with the sign of spontaneous polarization in the smectic-C* (SmC*) phase. Based on this observation, they proposed that the deviation originated from the electroclinic (EC) effect [6] in the SxnA phase induced by a localized surface field. Using a different LC material, Patel, Lee, and Goodby [5]found a large 0 and suggested that it is too large to be described by the surface EC effect. They proposed an alternative mechanism based on molecular twist via chirality and reduction of smectic ordering at the surface. Both models qualitatively explain some aspects of the experimental observations but not others so that a complete understanding of the phenomenon is still lacking.

Ferroelectric ordering and electroclinic effect in chiral smectic liquid crystals

“…The value of g is estimated to be 0.5 which indicates that the magnitude of the field-independent contribution is comparable to the fielddependent one, allowing effective mutual interference in accordance with (6). Symmetry axis shift dθ between opposite values of the voltage is about 52 o .…”

“…Then, according to (6) and (7), the temperature dependent contribution I 2ω (E, T ) in the absence of the electric field and for T < T c can be approximated by the following expression:…”

Surface electroclinic effect near the first-order smectic-A*–smectic-C*transition

“…1. The SECE has been analyzed, both experimentally and theoretically [1][2][3][4], for materials with a continuous Sm-A * -Sm-C * transition. The investigation of W415 [4] was notable in that an unusually large SECE was found and the effects of varying the enantiomeric excess were explored.…”

Alignment instability caused by anchoring of the in-plane directors to the rubbing direction in the V-shaped switching

“…19 This alignment behavior, of course, is dependent on the comparative value of the surface anisotropy and the molecule± surface polar interactions. Therefore, in the Sm-A phase of the open cell, the molecular alignment is easily explained.…”