Revolutionary developments in the fabrication of nanosized particles have created enormous expectations in the last few years for the use of such materials in areas such as medical diagnostics and drug-delivery, and in high-tech devices. By its very nature, nanotechnology is of immense academic and industrial interest as it involves the creation and exploitation of materials with structural features in between those of atoms and bulk materials, with at least one dimension limited to between 1 and 100 nm. Most importantly, the properties of materials with nanometric dimensions are, in most instances, significantly different from those of atoms or bulk materials. Research efforts geared towards new synthetic procedures for shape and size-uniform nanoscale building blocks as well as efficient self-assembly protocols for manipulation of these building blocks into functional materials has created enormous excitement in the field of liquid crystal research. Liquid crystals (LCs) by their very nature are suitable candidates for matrix-guided synthesis and self-assembly of nanoscale materials, since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level. Based on selected relevant examples, this review attempts to give a short overview of current research efforts in LC-nanoscience. The areas addressed in this review include the synthesis of nanomaterials using LCs as templates, the design of LC nanomaterials, self-assembly of nanomaterials using LC phases, defect formation in LC-nanoparticle suspensions, and potential applications. Despite the seeming diversity of these research topics, this review will make an effort to establish logical links between these different research areas.

Nanoparticles in Liquid Crystals: Synthesis, Self-Assembly, Defect Formation and Potential Applications

To explain the large isotope effect on the transition temperature in KH2P04, the tunnel­ ing motion of the protons in hydrogen bonds is considered and a theory of the phase transi­ tion is developed under the assumption that the ferroelectric behavior of this substance is due to cooperation of the ionic displacements, the interactions between ions and protons and the tunneling motion of protons. The relation between the present theory and the Slater model or the Blinc model is discussed. § I. Introduction In spite of the considerable amount of investigation made from the theo­ retical as well as the experimental side, the microscopic mechanism of the phase transition in KH2P04 and isomorphous crystals does not seem to be clearly un­ derstood. If . we classify the ferroelectric substances roughly into two groups, displacive and order-disorder type ferroelectrics, then KH2P04 will certainly belong to the latter group. However, the experimental data accumulated so far do not really give us a definite molecular picture of the phase transition, but sometimes reveals obvious inconsistencies among observed quantities. The main object of the present paper and a forthcoming one is to organize the somewhat divergent observed facts from the theoretical point of view and to suggest some experiments which might be helpful in attaining a full understanding of the phenomena. The crystal structure of KH2P04 (which will be abbreviated as KDP here­ after) is the so-called tetragonal diamond type. A characteristic feature of this structure is the existence of hydrogen bonds connecting two P04 tetrahedra, which run almost perpendicularly to the direction of the ferroelectric c axis. In the ferroelectric phase, the magnitude of the saturated polarization Ps is well accounted for by making use of the observed values for the displacements of ions K+I, p+ 5 and o- 2 along the c axis relative to their symmetric positions. 2 ),s) Therefore the hydrogen bonds do not contribute any appreciable dipole moments to the saturated polarization, and hence the essential unit of the dielectric prop­ erties in this crystal is the dipole moment of the complex [K-P04] as shown in Fig. 1. If KDP is of an " order-disorder " type of ferroelectric, that is, if the phase transition is caused by order-disorder arrangements of the dipole moments, the two configurations of the complex [K-P04] denoted as (A) and

Theory of Ferroelectric Phase Transition in KHzP04 Type Crystals. I

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880–2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C1 to C10. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C11 to C192. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C1-C10

In this Highlight article we will describe the current impact of nanoscale materials (nanoparticles and carbon nanotubes) in liquid crystal nanocomposites on the improvement of LC display (LCD) applications, an industry currently worth more than $60 billion per year. First tendencies clearly demonstrate the potential of nanomaterials to improve upon current LCD technologies with the discovery of new or modified switching modes, lower operating voltages, faster switching speeds, and higher contrast ratios—enormous advantages in a world with more LCDs than people (see ref. : D. W. Bruce, J. W. Goodby, J. R. Sambles and H. J. Coles, Introduction: New directions in liquid crystal science, Philos. Trans. R. Soc. London, Ser. A, 2006, 364, 2567–2571).

Impact of nanoscale particles and carbon nanotubes on current and future generations of liquid crystal displays

The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4′-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.

Hydrogen-bonded liquid crystals built from hydrogen-bonding donors and acceptors. Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties

Transformation of hydrogen bonding of a liquid crystal-aerosil system under the influence of an electric field

This paper describes detailed studies of the phase transitions and other physical properties of the series of 4-n-alkylbenzoic acids (CH3(CH2)nC6H4COOH) with alkyl groups ranging from propyl to heptyl.

A.A. Yakubov

Papers

Transformation of hydrogen bonding of a liquid crystal-aerosil system under the influence of an electric field

Polymorphic transitions in alkylbenzoic acids

Molecular interaction and ‘memory’ of filled liquid crystals

Polymorphism and intermolecular interactions in crystalline fluorinated alkylbenzoic acids

IR study of the cholesteryl n-alkanoates conformation mobility