How plants keep dry: a physicist's point of view

This work describes the investigation of the physical basis of the amazing water repellence of some plant leaves, which is in addition to self-cleaning properties known as the "Lotus effect". Two rather different possible mechanisms are proposed, which are suggested to cover the main physics in a majority of superhydrophobic systems. These concepts are illustrated with two different types of plant leaves as well as a model surface carrying carbon nanotube aggregates.     

Liquid crystals with a terminal oxime group

Two homologous series with the terminal oxime group are synthesized to evaluate the effect of the oxime group on mesogenic properties of the system. It is observed that oxime formation eliminates the smectic mesophases exhibited by parent homologous series. The nematic phase exhibited by mesogens has higher thermal stability because of intermolecular H-bonding.     

Liquid crystals with a 5-phenyltropone core

Liquid crystals with a 5-phenyltropone structure were prepared. 5-(4-Alkanoylaminophenyl)tropone derivatives ( 5 and 6 ) showed smectic A and C phases. From the layer spacing, compound 5q formed an interdigitated bilayer smectic A phase. The variable temperature FTIR spectra of 5q indicated the presence of intermolecular hydrogen bonding between the amide carbonyl group and the NH group on the phenyl ring of neighbouring molecules. The amide groups of the 2-alkanoylamino-5-phenyltropones controlled the occurrence of mesophases through not only inter- and intra-molecular hydrogen bonds, but also dipole-dipole interaction with the tropone carbonyl group of neighbouring molecules.     

Liquid crystals and life

The molecules of living systems invariably exhibit both thermotropic and/or lyotropic liquid crystalline properties. In some cases the mesophases formed by bio-materials have lamellar structures, whereas in other situations they form columnar phases. Many liquid crystal biomaterials are found in cell membranes, indicating that such structures have properties that are dependent on liquid crystallinity for their behaviour of a variety of bio-materials is discussed. function. In this article the mesomorphic     

Liquid crystals: first active organics in electronics

A Commentary on the paper “Anisotropic gels and plasticized networks formed by liquid crystal molecules”, by R. A. M. Hikmet. First published in Liquid Crystals, 9, 405-416 (1991).     

Liquid crystals: first active organics in electronics

A Commentary on the paper “Anisotropic gels and plasticized networks formed by liquid crystal molecules”, by R. A. M. Hikmet. First published in Liquid Crystals, 9, 405–416 (1991).     

Liquid crystals for display applications

Active Matrix (AM) LCDs and STN LCDs are the leading display technologies for portable applications such as notebook computers. Recently, new LCD device configurations and new LCD operation modes have been introduced. The existing technologies and the new LCD operation modes require improved liquid crystal materials. The history of liquid crystals for display applications and recent progress in new liquid crystal structures is presented.     

Liquid crystals from hydrogen-bonded amphiphiles

Liquid crystals originating from hydrogen-bonded amphiphiles will be discussed, highlighting the structural features of the amphiphilic components that lead to supramolecular systems exhibiting liquid crystalline character. Liquid crystalline phases derived from two types of hydrogen-bonded amphiphiles will be presented: (a) liquid crystalline phases originating from multihydroxylated amphiphiles; and (b) liquid crystalline phases resulting from combined hydrogen bonding and ionic interactions.     

Liquid crystals for active matrix displays

Active matrix liquid crystal displays belong to one of the fastest growing fields in display research and development. Several pocket TVs using this technology are already available commercially. High quality displays for TV and instrumentation require an understanding and optimization of liquid crystal material parameters. We have, therefore, investigated the influence of the elastic, dielectric and optic properties on the electrical resistance of the liquid crystal as well as on the response times and the viewing angle dependence of active matrix displays. Based on correlations derived from our investigations, we have developed new liquid crystals which have suitable properties and a very high electrical resistivity.     

Liquid crystals stabilized by polymer networks

This review is devoted to the characteristics of a new class of polymer composites, dispersions of chemical polymer networks in LCs. Photopolymerization of various bifunctional monomers in the medium of LCs leads to the formation of a polymer network that stabilizes the structure of crystals. Methods for the preparation of the above composites, their structure, morphology, and optical characteristic are reviewed, and areas of practical application of such materials are described.     

Liquid crystals stabilized by physical networks

This review concerns the behavior of a new class of LC composites with physical networks. These composites are prepared through the addition of some low-molecular-mass compounds (gelators) containing various functional groups to liquid crystals. In the medium of liquid crystals, gelators can form gels via non-covalent interactions, thereby stabilizing their structures. The structures of LC composites, their morphologies, and their optical and electro-optical properties are examined, and some application areas of these materials are illustrated.     

Liquid crystals for active matrix displays

Active matrix liquid crystal displays belong to one of the fastest growing fields in display research and development. Several pocket TVs using this technology are already available commercially. High quality displays for TV and instrumentation require an understanding and optimization of liquid crystal material parameters. We have, therefore, investigated the influence of the elastic, dielectric and optic properties on the electrical resistance of the liquid crystal as well as on the response times and the viewing angle dependence of active matrix displays. Based on correlations derived from our investigations, we have developed new liquid crystals which have suitable properties and a very high electrical resistivity.     

A view and a review of melting of alkali metal halide crystals

Theoretical models for the melting of solids are inadequate because relatively little is known about the structures of liquids formed and the factors that control this phase transformation. In the present analysis of fusion phenomenon, usually considered to be a physical change, it is pointed out that, for many solids (e.g., metals and some simple ionic salts) melting involves the redistribution of primary valence bonds. Accordingly, this review includes examination some more chemical aspects of the controls of melting. The available data show that enthalpy and density changes during liquefaction and solidification of the metallic elements and of the alkali halides are small. From quantitative consideration of these values, it is concluded that ordered packing arrangements of atoms, ions, or molecules, comparable with those of crystals, must be extensively retained into the melt. The energy and molar volume changes on melting are too small to allow significant departure, in the liquid, from the regular, efficient space-filling arrays that characterize crystalline solids. The set/liq model for melting (dynamic equilibria between alternative ordered structures) is proposed to account for the properties of the liquid. A detailed and critical comparison of melting with solid state decompositions considers the kinetics and the mechanisms of the changes that occur during the supply/removal of energy to/from the melt/crystal contact interface. Other relevant aspects of melting are discussed including the factors that determine the magnitudes of the melting points of individual solids.     

Liquid crystals and biological morphogenesis: Ancient and new questions

Superposed series of arcs were observed in extracellular matrices of diverse tissues in plants and animals, and also within certain chromosomes. These bow-shaped patterns were shown to originate from oblique sections in a three-dimensional arrangement of fibrils, which was reminiscent of a well-known structure present in a specific type of liquid crystal, called “cholesteric”, since it was first described in several cholesterol esters. These liquid crystals were also obtained with numerous chiral polymers, such as double-stranded nucleic acids, diverse polypeptides and polysaccharides. However, the fibrous matrices with arced patterns are not at all fluid in general and are considered as stabilized analogues of cholesteric liquid crystals. These geometrical similarities between fibrous tissues and liquid crystals were at the origin of numerous works defining a new type of self-assembly involving two successive steps: a phase transition from an isotropic liquid phase to a liquid crystalline one, followed by a sol–gel stabilization of the liquid crystal. One is tempted to apply to these biological materials the main concepts introduced by physicists in the field of liquid crystals, but many aspects require a new discussion, especially because living cells are present in such systems, and this opens considerable perspectives for research.     

Liquid crystals derived from 2-phenylisoindoles: synthesis and characterization

2-Phenylisoindole was investigated as the rigid core unit in a series of asymmetric mesogenic molecules. When the 2-phenylisoindole core was terminated with a hexyl tail, no mesophase formation could be observed. When 4- n -(tridecafluorohexyl) was used, however, both monotropic and enantiotropic phase behaviour were observed. It was found that most functionalities at the anhydride 5-position results in the formation of smectic A (SmA) phases in the temperature range 70-180°C. Functionalities at the anhydride 4-position suppress mesophase formation. Large substituents (-Br, -NO2) and symmetric substitution patterns (5,6-dichloro, 4,7-dichloro and 4,5,6,7-tetrachloro) on the anhydride moiety increase the melting point and destabilize the mesophase. Temperature dependent X-ray diffraction experiments suggest an interdigitated SmA packing for this family of compounds.     

The systems-theoretical view of chemical concepts

While the principal ideas of a systems theory for the molecular sciences have been introduced in part I (Reiher, 2003), illustrative examples for the ingredients of this systems chemistry are discussed in greater detail in this work. The potential wealth of systems chemistry is then demonstrated for a recently developed approach for the calculation of hydrogen bond energies in non-decomposable systems. This revised version was published online in July 2006 with corrections to the Cover Date.