Pressure-induced formation of diblock copolymer "micelles" in supercritical fluids. A combined study by small angle scattering experiments and mean-field theory. II. Kinetics of the unimer-aggregate transition

We developed a simple time-dependent mean-field theory to describe the phase separation kinetics of either homopolymers or AB-diblock copolymers in supercritical (SC) fluids. The model, previously used to describe the phase behavior of AB-block copolymers under the assumption of strong solvent selectivity for just one copolymer chain, has been extended to study the kinetics of the phase separation process. Time resolved small angle x-ray scattering (TR-SAXS) measurements have been performed on different AB-diblock copolymers containing a perfluorinated chain and dissolved in SC-CO2. The data obtained over a wide range of pressure and temperature confirm our theoretical predictions. Particul…

Supra Aggregates of Fibers-Forming Anisotropic Molecules: theory and experiments by Scanning Force Microscopy

Patterning by Langmuir-Blodgett monolayers

Kinetics of Molecule Transfer between Lipid Vesicles and β-Cyclodextrins

Abstract We propose a calorimetric method based on the van't Hoff model of depression of the freezing temperature to investigate slow kinetics involving lipid vesicles (liposomes) and drug–β-cyclodextrin (Cyd) complexes. Some nonsteroidal antiinflammatory drugs (NSAIDs) were examined and standard phospholipid liposomes were used in our experiments. Three different kinetic processes were investigated: (a)9Transfer of drugs from water-soluble Cyd-complexes to void liposomes. (b)9Uptake of drugs from the surface of liposomes by free Cyd dissolved in the aqueous phase. (c)9Exchange of drugs from loaded to void vesicles, and the effect of free Cyd in enhancing such a transfer. Most experiments w…

Self-assembling of fiber forming anysotropic molecules

Switching direction of laterally ordered monolayers induced by transfer instability

Langmuir-Blodgett monolayers may show nanoscopic periodic patterns parallel and/or perpendicular to the transfer direction. The experimental findings are interpreted by a nonequilibrium model based on the stability of surfactant concentration and film thickness coupled fluctuations near the meniscus of a surfactant-covered receding thin film. In the high and low transfer speed limits, periodic fluctuations of the fluid subphase thickness, respectively perpendicular and parallel to the transfer, are selected. A qualitative phase diagram shows how transfer speed and film density manage the pattern shape.

Pressure-Induced Formation of Diblock Copolymer "Micelles" in Supercritical Fluids. A Combined Study by Small Angle Scattering Experiments and Mean-Field Theory. I: the Critical Micellization Density Concept

We developed a simple mean-field theory to describe polymer and AB diblock copolymer phase separation in supercritical (SC) fluids. The highly compressible SC fluid has been described by using a phenomenological hole theory, properly extended to consider the solvent/polymer/vacancy pseudoternary mixture. The model has been applied to describe the phase behavior of AB-diblock copolymers under the assumption of a strong solvent selectivity for just one copolymer chain. In our model the solvent selectivity is a strong function of the external pressure because in compressible fluids vacancies reduce the number of favorable solvent-polymer contacts. The combined effect of the pressure on the ave…