Heinz Amenitsch

Humidity-controlled mesostructuration in CTAB-templated silica thin film processing. The existence of a modulable steady state

A study is presented of the self-assembly process that takes place during CTAB-templated silica film formation through in situ SAXS, interferometry and water titration investigations during evaporation associated with dip coating under various conditions. This work shows that the quantity of water present in the film when the mesostructuration takes place depends on the relative humidity (RH) during deposition. Indeed, the system contains considerable quantities of water at high RH, while it loses water at low RH. The water content is demonstrated to be a critical parameter, as poorly ordered, 2D-hexagonal or 3D-cubic final structures are obtained, depending on the RH, in agreement with the general physico-chemical laws of CTAB mesophases. Furthermore, changing the RH or the solvent vapour pressure just after evaporation induces a film composition change and a potential mesostructure modification, evidencing a modulable steady state, during which the mesostructure can be modified by external influences. The present study pinpoints the role of processing conditions that are often considered secondary to chemical conditions. The conclusions of this study into the CTAB–TEOS system are also relevant to other surfactant-templated systems which undergo evaporation-controlled self-assembly.

Impurities in Commercial Phytantriol Significantly Alter Its Lyotropic Liquid-Crystalline Phase Behavior

The lyotropic liquid-crystalline phase behavior of phytantriol is receiving increasing interest in the literature as a result of similarities with glyceryl monooleate, despite its very different molecular structure. Some differences in the phase-transition temperature for the bicontinuous cubic to reverse hexagonal phase have been reported in the literature. In this study, we have investigated the influence that the commercial source and hence the purity has on the lyotropic phase behavior of phytantriol. Suppression of the phase-transition temperatures (by up to 15 degrees C for the bicontinuous cubic to reverse hexagonal phase transition) is apparent with lower-purity phytantriol. In addition, the composition boundaries were also found to depend significantly on the source and purity of phytantriol, with the bicontinuous cubic phase + excess water boundary occurring at a water content above that reported previously (i.e., >5% higher). Both the temperature and compositional changes in phase boundaries have significant implications on the use of these materials and highlight the impact that subtle levels of impurities can play in the phase behavior of these types of materials.

Small angle X-ray scattering analysis of deoxyguanosine 5'-monophosphate self-assembing in solution: nucleation and growth of G-quadruplexes.

To solve details of the self-assembling process of guanosine in diluted aqueous solution and to derive a thermodynamical model for quadruplex formation, the structural behavior of deoxyguanosine 5-monophosphate has been analyzed by in-solution small angle X-ray scattering. The experiments have been performed as a function of guanosine concentration and at fixed guanosine concentration but in the presence of varying amounts of KCl. As a result, the self-assembling process, in terms of both aggregate particle fractions and aggregate length, has been observed to be strongly dependent on composition and largely affected by excess potassium ions in the solution. In particular, the different aggregate forms have been resolved and their concentration derived as a function of sample composition. In accordance with a hierarchical aggregation process, a nucleation and elongation mechanism has been used to derive the thermodynamical parameters for self-assembling. The results show that the annealing and fragmentation steps play an important role in the aggregation process.

Presmectic wetting and supercritical-like phase behavior of octylcyanobiphenyl liquid crystal confined to controlled-pore glass matrices.

The influence of controlled-pore glass (CPG) confinement on the phase behavior of octylcyanobiphenyl liquid crystal (LC) is studied by means of x-ray scattering and high precision calorimetry. For CPG samples with pore diameter 2R>24 nm, the smectic order parameter temperature dependence eta(T) reveals apparent presmectic ordering far above the bulk smectic A-nematic (SmA-N) phase transition for both nontreated and silane-treated CPG matrices. The behavior of eta(T) is qualitatively similar in all samples, well obeying the mean field approach (MFA) in which the surface wetting tendency plays the dominant role. In contrast, the critical fluctuations remain important in the specific heat data, which cannot be described within the MFA. We show experimentally that randomness and surface wetting become dominant over finite-size effects for 2R approximately<10 nm, in agreement with theoretical analysis. In nontreated samples, the noncritical character of the static disorder and the interfacial LC-CPG coupling almost completely suppress the quasi-SmA-N and nematic-isotropic phase transitions at 2R approximately 15.1 and approximately 7.5 nm, respectively.

Self-organization of synthetic cholesteryl oligoethyleneglycol glycosides in water.

Lectin-sugar recognition systems are of interest in the pharmaceutical field, especially for the development of drug carriers, tailored for selective delivery. This paper deals with the anhydrous and aqueous self-organization properties of a synthetic cholesteryl oligoethyleneglycol glycoside with the aim of their incorporation in liposomes. Successive phases (lamellar, R3m, Im3m, micelles) have been described depending on water content and temperature. As a result of the presence of sugar residues and their hydration ability, this glycolipid shows a large range of packing parameter with increasing water content. However, because of oligoethyleneglycol spacer, a slight dehydration has been observed with increasing temperature from 20 to 60 degrees C.

Low-dimensionality effects in the melting of a Langmuir-Blodgett multilayer.

Low-dimensionality effects in the melting behavior of a cadmium arachidate Langmuir-Blodgett multilayer have been studied. Depth resolved information about structural changes occurring with temperature is obtained using in-plane X-ray diffraction under standing wave conditions. The surface region exhibits a distinctly different melting behavior as compared to the bulk of the film. While in the bulk of a 13-monolayer cadmium arachidate multilayer, the crystalline phase directly transforms to a tilted hexaticlike phase at 360 K, in the near surface region transformation occurs via an intermediate smectic phase. This behavior of the surface region is similar to that observed in two-dimensional crystals. Thus even in a thick Langmuir-Blodgett multilayer, the surface region exhibits low-dimensionality effects.

Smectic Ordering of 8CB Liquid Crystal Confined to a Controlled-Pore Glass

ABSTRACT We study the temperature evolution of smectic ordering of 8CB liquid crystal confined to various CPG matrices. The characteristic diameters of matrices ranged from 24 nm to 128 nm. The CPG voids were either left non-treated or were treated with silane. A weakly 1st order N-SmA transition in bulk 8CB, which could be attributed to the Halperin-Lubensky-Ma (HLM) effect, is broadened in confined samples. In confined samples substantial pretransitional anchoring was also observed, particularly in the silane-treated samples.