Induced liquid crystals

Some materials are themselves not liquid crystals, or do not display the liquid crystal phase at a certain temperature or solvent concentration. But, 

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The phase behavior of surfactant systems is particularly complex because of the existence of numerous lyotropic (solvent-induced) liquid crystal phases (3). These phases, like liquids and crystals, are discrete states of matter. They are fluids, but their x-ray patterns display sharp lines signifying the existence of considerable structure. They are often extremely viscous because of their high viscosities and for other reasons they are difficult to study using conventional methods. This is evident from the fact that serious errors in the presumably well-established classical aqueous phase diagrams of soaps, sodium alkyl sulfates, monoglycerides, and... 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

Patterning a polymer film to induce liquid crystal orientation... 

Presnyakov V, Asatryan K, Galstian T, Chigrinov V. 2006. Optical polarization grating induced liquid crystal micro structure using azo dye command layer. Opt Expr 14 10558 10564. 

Minoofar P.N., Hernandez R., Chia S., Dunn B., Zink J.I., FranvUle A.-C. Placement and characterization of pairs of luminescent molecules in spatially separated regions of nanostructured thin films. J. Am. Chem. Soc. 2002 124 14388-14396 Miyata H., Itoh M., Watanabe M., Noma T. Preparation of highly ordered mesostructured tin oxide film with a microcrystalline framework through vapor-induced liquid-crystal templating. Chem. Mater. 2003 15 1334-1343... 

Y. Liao, Ch. Hsn, and S. T. Wu, Dipping and photo-induced liquid crystal alignment using silane snrfactants. Japanese Journal of Applied Physics 39, L-90 (2000). 

S. Gong, J. Kanicki, L. Ma, and J. Zhong, Ultraviolet-light induced liquid-crystal ahgnment on polyimide films. Japanese Journal of Applied Physics 38, 5996 (1999). 

S.-J. Sung, H.-T. Kim, J.-W. Lee, and J.-K. Park, Photo-induced liquid crystal ahgnment on polyimide containing fluorine group. Synthetic Metals 117, 277 (2001). 

Figure 4.17 Experimental setup for forming the polarization grating in photoahgnmg layer SDl X/2, half-wave plate for power balance between interfering beams BE, beam expander BS, beam splitter PG, Gian prism X/4, quarter-wave plates [57]. Reproduced from V. Presnyakov, K. Asatiyan, T. Galstian, and V. Chigrinov, Optical polarization grating induced liquid crystal micro-structure using azo-dye command layer. Optics Express 14, 10558 (2006), Optical Society of America...

As witli tlie nematic phase, a chiral version of tlie smectic C phase has been observed and is denoted SniC. In tliis phase, tlie director rotates around tlie cone generated by tlie tilt angle [9,32]. This phase is helielectric, i.e. tlie spontaneous polarization induced by dipolar ordering (transverse to tlie molecular long axis) rotates around a helix. However, if tlie helix is unwound by external forces such as surface interactions, or electric fields or by compensating tlie pitch in a mixture, so tliat it becomes infinite, tlie phase becomes ferroelectric. This is tlie basis of ferroelectric liquid crystal displays (section C2.2.4.4). If tliere is an alternation in polarization direction between layers tlie phase can be ferrielectric or antiferroelectric. A smectic A phase foniied by chiral molecules is sometimes denoted SiiiA, altliough, due to the untilted symmetry of tlie phase, it is not itself chiral. This notation is strictly incorrect because tlie asterisk should be used to indicate the chirality of tlie phase and not tliat of tlie constituent molecules. 

If we compare with figure C2.2.I I, we can see that this defonnation involves bend and splay of the director field. This field-induced transition in director orientation is called a Freedericksz transition [9, 106, 1071. We can also define Freedericksz transitions when the director and field are both parallel to the surface, but mutually orthogonal or when the director is nonnal to the surface and the field is parallel to it. It turns out there is a threshold voltage for attaining orientation in the middle of the liquid crystal cell, i.e. a deviation of the angle of the director [9, 107]. For all tliree possible geometries, the threshold voltage takes the fonn [9, 107]... 

T. Gruhn, M. Schoen. Substrate-induced order in confined nematic liquid-crystal films. J Chem Phys 705 9124-9136, 1998. 

Our results [104,117] have shown that the extended chains of ethyl cellulose liquid crystal at high pressures can act as the nucleus of PE ECC and induce the formation of ECC. (The details will be introduced in Section IX.)... 

Another example of the coupling between microscopic and macroscopic properties is the flexo-electric effect in liquid crystals [33] which was first predicted theoretically by Meyer [34] and later observed in MBBA [35], Here orientational deformations of the director give rise to spontaneous polarisation. In nematic materials, the induced polarisation is given by... 

The response of liquid crystal molecular orientation to an electric field is another major characteristic utilised for many years in industrial applications [44] and more recently in studies of electrically-induced phase transitions [45]. The ability of the director to align along an external field again results from the electronic structure of the individual molecules. 

The interaction of complex liquid crystal molecules with realistic surfaces is an area which is currently unexplored using electronic structure methods though, as stated earlier, the problem of surface-induced control of molecular orientation remains at the forefront of liquid crystal device technology. This problem is currently at the limits of practical capability of the most powerful computer systems. However treatment of a single mesogenic molecule on a... 

Stelzer et al. [109] have studied the case of a nematic phase in the vicinity of a smooth solid wall. A distance-dependent potential was applied to favour alignment along the surface normal near the interface that is, a homeotropic anchoring force was applied. The liquid crystal was modelled with the GB(3.0, 5.0, 2, 1) potential and the simulations were run at temperatures and densities corresponding to the nematic phase. Away from the walls the molecules behave just as in the bulk. However, as the wall is approached, oscillations appear in the density profile indicating that a layered structure is induced by the interface, as we can see from the snapshot in Fig. 19. These layers are... 

Firouzi, A Schaefer, DH Tolbert, SH Stucky, GD Chmelka, BE, Magnetic-Field-Induced Orientational Ordering of Alkane Lyotropic Silicate-Surfactant Liquid Crystals, Journal of the American Chemical Society 119, 9466, 1997. 

First, it is important to appreciate that all liquid crystal mesophases exist due to non-covalent interactions between molecules, namely the anisotropic dispersion forces mentioned earlier. However, this section will address more specific non-covalent interactions that have been used either to induce liquid-crystalline behaviour or to generate a new species that is liquid crystalline. 

For example, Marder and co-workers [10] (among others) have studied liquid crystal mesophases induced by the presence of quadrupolar interactions between non-mesomorphic phenyl- and perfluorophenyl-containing moieties (e.g. 1). 

N.m.r. studies of liquid crystal media showed that phenyl sulphonate counter ions induced abrupt changes in the dipolar coupling of methy1phosphonate. 61... 

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