Two Types of Anchoring Structure in Smectic Liquid Crystal Molecules

Abstract

The anchoring structures of smectic liquid crystals, n-alkylcyanobiphenyl (mCB: m=8, 10, 12), on molybdenum disulfide (MoS2) are directly observed by scanning tunneling microscopy (STM) in order to analyze the alignment mechanism of liquid crystals. For 8CB, the anchoring structure is of the periodic monolayer type, while 10CB and 12CB take a bilayer structure in which there is no interdigitation of the cyano groups. These structures on MoS2 depend on the length of the alkyl group in contrast to those on graphite. The mechanism of alignment is discussed based on the STM results.

Liquid Crystals — as seen by the Scanning Tunnelling and Force Microscopes

“…The attractive contacts between rows also come from head-to-head and tail-totail interactions. 9CB and 11CB pack similarly on MoS 2 [7]. 10CB and 12CB maintain nearly the same pack ing pattern on MoS 2 as on graphite.…”

“…The well -studied class of cyanobiphenyl liquid crystals has also been imaged on MoS 2 [7], and the resulting molecular patterns have been compared to those from graphite (Fig. 8) .…”

Anchoring Phase of Liquid Crystal Mixtures Studied by Scanning Tunneling Microscopy

“…As both the alkyl chain and cyanobiphenyl in 8CB are about 11 A long, those liquid crystals can be recognized as 8CB molecules, following the same manner as we discussed in our previous paper. 6 The STM images of pure 8CB samples, on the other hand, exhibited a homogeneous single-row structure in which cyanobiphenyl head groups and long alkyl tails alternate in each row. 4 Figure 3a shows a model of the anchoring structure in the homogeneous 8CB single-row (a)80:20 (0.3nA,1.6V,15x15nm) (b)70:30 (0.3nA,1.0V,15x15nm)(c)60:40 (0.2nA,2.0V,20x20nm) 8CB Single Row (C-S-N-l) 8CB Single Row (C-S-N-l) Mixed Double Row (C-S-l) (d)30:70 (0.2nA, 1 9V,20x20nm) (e)20:80 (0.3nA,1.6V,20x20nm) (f)10:90 (0.2nA,1.1 V,20x20nm)…”

Kinked row-induced chirality driven by molecule–substrate interactions

“…When the number of methylene units n (n = 5, 6, 7, 8, 9, 10, 12) varies, the molecular ordering on crystalline substrates may change. This effect was evidenced on highly oriented pyrolytic graphite (HOPG) [28][29][30][31][32] and molybdenum disulfide (MoS 2 ) [33][34][35][36] substrates. It has been shown that the n-CB molecular rows can be kinked, inducing a specific kind of chirality related to the direction of the kinks 13 .…”