Liquid Crystalline State Of Matter Research Articles

Chemical and biological sensing using liquid crystals

The liquid crystalline state of matter arises from orientation-dependent, non-covalent interactions between molecules within condensed phases. Because the balance of intermolecular forces that underlies the formation of liquid crystals (LCs) is delicate, this state of matter can, in general, be easily perturbed by external stimuli (such as an electric field in a display). In this review, we present an overview of recent efforts that have focused on exploiting the responsiveness of LCs as the basis of chemical and biological sensors. In this application of LCs, the challenge is to design liquid crystalline systems that undergo changes in organization when perturbed by targeted chemical and biological species of interest. The approaches described below revolve around the design of interfaces that selectively bind targeted species, thus leading to surface-driven changes in the organization of the LCs. Because LCs possess anisotropic optical and dielectric properties, a range of different methods can be used to read out the changes in organization of LCs that are caused by targeted chemical and biological species. This review focuses on principles for LC-based sensors that provide an optical output.

FROM BULK JANOSSY EFFECT TO NONLINEAR SELF WAVE-GUIDING OR SPATIAL SOLUTION IN DYE-DOPED LIQUID CRYSTALS

The pure liquid crystalline state of matter is known for its large optical nonlinearity. The effect has been widely studied in thin film as the beam crosses it. Few studies have been done for a geometry in which the light interacts with the matter on a large volume. In this paper, we report the results we have obtained in this configuration (Bulk Optical Freederisckz Effect) and for dye-doped liquid crystals. In such mixtures, the nonlinear effect occurs at low input powers and is called the Janossy effect. Besides similar behaviors which occur in the Bulk Freederisckz Effect, it is reported in this paper a beam behavior, namely a self wave-guiding or "spatial soliton," which is probably more specific to the bulk Janossy Effect. This self created wave-guide is assigned to be a consequence of the dye absorption: the optically induced refractive index gradient is finely tuned by the additional anisotropic thermal contribution, allowing a quasi perfect optical coupling of the fiber source with the optically induced liquid crystal wave-guide.

Cholesteric liquid Crystals: Physical Properties and Molecular-Statistical Theories

Abstract It seems certain now that cholesteric liquid crystals (cholesterics, or CLC, for short) have been the first examples of mesomorphic state of matter known to humankind. Apart from the well-known discovery of the two-stage melting of cholesteryl benzoate made by Reinitzer in 18881 and cited in almost all the textbooks, one may recall some other papers where the authors, quite unaware of the real significance of their observations, presented undeniable evidence of the liquid crystalline state of matter. E.g., Professor Planer from the Lvov University as early as in 1861 did observe, putting it in the presentday terms, selective reflection from the planar texture of cholesteryl chloride forming a monotropic cholesteric mesophase on cooling.2 One should also note that the works of Fergason3,4 outlining the prospects of practical applications for CLC, did, in fact, precede similar endeavors by Heilmeier in the field of nematics. From the viewpoint of organic chemistry, a number of mesogenic cholesterol...

Structures and properties of the liquid crystalline state of matter

Liquid crystals were discovered in 1888 but have been studied seriously during the past 20 years. The kinds of molecules that form liquid crystals on heating and by mixing two or more substances are explained. Properties of liquid crystals and related structural characteristics are summarized. The properties considered include optical characteristics, textures, and the role of water in lyotropic systems. The structures of nematic and smectic liquid crystals are explained and systemized. Determination of the tilt angle of the molecules in the smectic C compounds terephthal-bis-(4, n-butylaniline) (TBBA and its C 5 and C 6 homologs) is discussed. The molecular packings in the crystalline forms of three nematogenic compounds are explained.

Properties and applications of liquid crystals

This paper is a brief review of some of the properties and applications of liquid crystals. References will guide the reader to more extensive presentations. Molecular geometry is important in interpreting the properties of liquid crystals. Certain aspects of molecular geometry are discussed along with classification of the different types of liquid crystals. The molecular packings in some liquid crystalline structures are presented and correlated with some of the behaviors of the liquid crystalline state of matter. Optical properties which relate to applications of liquid crystals are described. Applications of liquid crystals are focused on three common areas. These include the use of cholesteric materials (spontaneously twisted nematic liquid crystals) in non-destructive testing in industrial laboratories and in medical clinics; the use of liquid crystals in displays; and the use of liquid crystals as solvents.

Properties of Liquid Crystals

Molecular geometry is important in interpreting the properties of liquid crystals. In addition, the molecular packing in different liquid crystalline structures will be presented and correlated with the properties of the liquid crystalline state of matter. This information on molecular packing will be focused essentially on thermotropic liquid crystals, but some information will be presented on lyotropic ones. A brief synopsis of some of the most interesting applications of liquid crystals will be presented.