AFM and optical investigations of liquid crystal dewetting: Influence of short and long-range forces

We have investigated the dewetting morphology of thin films of the liquid crystals 5AB 4 and 5AB 3, from a silicon substrate. For 5AB 4, nucleation and spinodal dewetting can be clearly identified, and from scanning force microscopy of the liquid profiles, details of the effective interface potential can be quantitatively inferred. Due to peculiarities of the wetting forces in this system, the analogy to spinodal decomposition is particularly close. With 5AB 3, an additional, rather complicated dewetting scenario is observed which is connected to the crystallization of droplets which have formed during the initial dewetting process

Layering Transitions and Reentrant-Like Phenomenon in Thin Films of Three-Block Organosiloxane Smectogens at the Air/Water Interface

The surface pressure induced layering transition of three-block amphiphilic smectogens at the air/water interface is observed and characterized by film balance measurements, Brewster angle microscopy and X-ray reflectivity. Since the systems possess a fluid smectic A bulk phase the transition is reversible with little hysteresis and occurs layer by layer. Wheareas the monolayer at the air/water interface exhibits polar smectic C-like order the multilayer is in a smectic A arrangement equivalent to that in bulk. The reentrant-like transition can be ascribed to a loss of order of water surrounding the hydrophilic head when removing molecules from the water surface. The thickness uniformity and stability may be ascribed to the line tension related to a domain boundary and to long-range van der Waals forces between interfaces. The mono-as well as multilayers can be transferred onto solid substrate apparently without any major structural changes

Columnar to nematic mesophase transition in mixtures of rhodium or copper soaps with hydrocarbon solvents

This paper describes observations of the mesomorphic behaviour of mixtures of rhodium eicosanoate or copper dodecanoate with solvents such as toluene, decahydronaphthalene, and (+) camphene. The mesophase found with these compounds at high temperatures turns from columnar to nematic when the weight fraction of the solvent (toluene, decahydronaphthalene is increased beyond a value of about 50 %. The binary phase diagram of the copper compound with toluene was experimentally determined using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The novel feature of the nematic phase is that the basic physical object which align parallel to the nematic director are not individual molecules, but columns of molecules (one-dimensional supramolecular assemblies) which have lost the long-range lateral positional order characteristic of the columnar mesophase. These observations are discussed on the grounds of recent theoretical calculations. Cholesteric-like textures are observed for mixtures of rhodium eicosanoate with the chiral solvent (+) camphene