Karel Procházka

Dilute and semidilute solutions of ABA block copolymer in solvents selective for A or B blocks: 2. Light scattering and sedimentation study

Abstract Micellar solutions of a triblock copolymer polystyrene- block -poly(hydrogenated butadiene)- block -polystyrene, in heptane and in 1,4- dioxane 25 vol % heptane have been studied by light scattering and sedimentation velocity methods. In dilute solutions, micellar molar mass, hydrodynamic radius of micelles, average volume fraction of polymer segments in a micellar core and in the whole micelle, and the unimer/micelles ratio have been determined. While in semidilute mixed solvent solutions only one diffusion mode, corresponding to collective diffusion, has been determined, at least two modes, diffusion and relaxation ones, have been observed in spectra of decay times in semidilute heptane solutions. Micellar models have been proposed for both systems under study, accommodating satisfactorily all experimental results.

Polyelectrolyte-surfactant complexes formed by poly[3,5-bis(trimethylammoniummethyl)4-hydroxystyrene iodide]-block-poly(ethylene oxide) and sodium dodecyl sulfate in aqueous solutions.

Formation of polyelectrolyte-surfactant (PE-S) complexes of poly[3,5-bis(trimethylammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) and sodium dodecyl sulfate (SDS) in aqueous solution was studied by dynamic and electrophoretic light scattering, small-angle X-ray scattering (SAXS), atomic force microscopy, and fluorometry, using pyrene as a fluorescent probe. SAXS data from the QNPHOS-PEO/SDS solutions were fitted assuming contributions from free copolymer, PE-S aggregates described by a mass fractal model, and densely packed surfactant micelles inside the aggregates. It was found that, unlike other systems of a double hydrophilic block polyelectrolyte and an oppositely charged surfactant, PE-S aggregates of the QNPHOS-PEO/SDS system do not form core-shell particles and the PE-S complex precipitates before reaching the charge equivalence between dodecyl sulfate anions and QNPHOS polycationic blocks, most likely because of conformational rigidity of the QNPHOS blocks, which prevents the system from the corresponding rearrangement.

Small-Angle Neutron Scattering Study of Onion-Type Micelles

Onion-type block copolymer micelles were prepared drom polystrene-block-poly(2-vinylpridine) (PS-b-PVP) inner micelles in an acidic solution by basyfyting in the presence of polystrene-block-poly(2-vinylpridine)-block-poly(ethylene oxide) (PVP-b-PEO). This has the effect of depositing the PVP-b-PEO onto the collapsed corona of the PS-b-PVP micelle. These core PS-b-PVP micelle, the small micelles formed by PVP-b-PEO, and the resulting onions micelles were studied by small angle neutron scattering (SANS) techniques . Two recently developed evaluation techniques were employed: 1.Bare-core approximation, which utilizes the data at larger scattering anles provided information about the size and polydispersity of the micelle core. 2. Application of the Pedersen and Gerstenberg micelle model, which utilizes the whole scattering curve. Due to their polyelectrolyte nature, the core micelles had very extentde coronas corresponding to rather large stastistical segment lengths. The SANS data at large scattering angles for the solution of onions-type micelles revealed the presence of a significant number of the small PVP-b-PEO micelles. The contribution of the small micelles to the total scattering was subtracted and the properties and polydispersities of onions cores and stabilizing PEO coronas were obtained.

Interaction of fluorescently substituted metallacarboranes with cyclodextrins and phospholipid bilayers: fluorescence and light scattering study.

We prepared two fluorescein-[3-cobalt(III) bis(1,2-dicarbollide)](-) conjugates. They are sparingly soluble in water and form large aggregates in aqueous solutions. An extensive study on their spectral and aggregation behavior was carried out. To prepare their well-defined dispersion in aqueous systems, we studied the interaction of both probes with two biocompatible amphiphilic systems, cyclodextrins, which are frequently used in drug-delivery systems, and phospholipid membranes, which are the major constituents of cell barriers in living organisms. The presence of fluorescein in both conjugates allows us to study their behavior in detail by steady-state and time-resolved fluorometry, fluorescence correlation spectroscopy, and fluorescence lifetime imaging. The self-assembly of these metallacarboranes in aqueous solutions was studied by dynamic light scattering. The study shows that the compounds interact with cyclodextrins that increases their solubility in water, and they solubilize easily in phospholipid bilayers.

Molecular dynamics simulations of a polyelectrolyte star in poor solvent

We used Molecular Dynamics (MD) simulations to investigate the conformations of a star polyelectrolyte in poor solvent. We observed several distinct morphologies: at low number of arms, pearl-necklace structures are formed on individual arms; at higher number of arms inter-arm bundling is the dominant structural motif.

Adsorption of self-avoiding walks at an impenetrable plane in the expanded phase: a Monte Carlo study

We consider self-avoiding walks on the simple cubic lattice, confined to the half-space z0. In addition, the walks interact with the plane z = 0 and have a vertex-vertex interaction. The walks can adsorb at the plane z = 0. The location of the adsorption phase transition depends, in general, on the contact interaction. We use Monte Carlo methods to investigate the form of the adsorption phase boundary in the expanded phase region.

Formation of block copolymer micelles: a sedimentation study

Abstract The formation of block copolymer mixed micelles has been studied in solutions of polystyrene-block-polyisoprene and polystyrene-block-poly(ethylene-co-propylene) in decane, a selectively poor solvent for polystyrene blocks. The rate of mass exchange between two types of micelles, studied by the sedimentation velocity method, depends strongly on the rates of micelle formation and dissociation processes, which can be controlled by temperature.

pH-dependent self-assembly of polystyrene-block-poly((sulfamate-carboxylate)isoprene) copolymer in aqueous media.

The amphiphilic polystyrene- block-poly((sulfamate-carboxylate)isoprene) (PS-PISC) diblock copolymer was synthesized from the precursor diblock copolymer polystyrene- block-isoprene by reaction with chlorosulfonyl isocyanate. The structure and behavior of self-assembled PS-PISC nanoparticles was studied in alkaline and acidic aqueous solutions by a combination of static and dynamic light scattering, analytical ultracentrifugation, atomic force and cryogenic transmission electron microscopies, NMR spectroscopy, potentiometric titration, and fluorometry using pyrene as a polarity-sensitive fluorescent probe. It was found that PS-PISC exists in aqueous solutions in the form of micellar aggregates. The aggregation tendency increases with decreasing effective charge density in the shell, that is, with decreasing pH of the solution, and aggregates found in alkaline aqueous media have much smaller molar masses than those formed in acidic media. The latter are dense, collapsed structures with immobile PISC domains in which most of the COOH and NH 2 (+)SO 3 (-) groups are buried inside of the nanoparticles. The swelling of PISC domains and disentanglement of PISC chains after addition of a base are slow processes occurring on the time scale of days.

Polyelectrolyte shells of copolymer micelles in aqueous solutions: A Monte Carlo study

Multimolecular micelles, formed by polystyrene-block-poly(methacrylic acid) in water, are studied by lattice Monte Carlo method. Electrostatic interactions are calculated in the mean-field approximation by solving the Poisson-Boltzmann equation. The model is parametrized according to available experimental data. The dependence of micellar size on pH and ionic strength is calculated and compared with experimental data. A special attention is devoted to the behavior in solutions with a low ionic strength.

Micelle-like nanoparticles of block copolymer poly(ethylene oxide)-block-poly(methacrylic acid) incorporating fluorescently substituted metallacarboranes designed as HIV protease inhibitor interaction probes.

We prepared nanoparticles differing in morphology from double-hydrophilic block copolymer poly(ethylene oxide)-block-poly(methacrylic acid), PEO-PMA, and two types of fluorescein-[3-cobalt(III) bis(1,2-dicarbollide)] conjugates, GB176 and GB179, in alkaline buffer. GB176 molecule consists of fluorescein attached to the metallacarborane anion. In GB179 molecule, the fluorescein moiety connects two metallacarborane anions. The self-assembly is based on the unusual interaction of metallacarborane clusters with PEO blocks which form insoluble micellar cores. The GB176 containing nanoparticles are loose and irregular, while the GB179 ones are rigid and spherical. The structure of nanoparticles depends to some extent on a procedure of preparation. The micelles were studied by static and dynamic light scattering, fluorometry and atomic force microscopy. Since the metallacarborane conjugates act as potent inhibitors of HIV protease, the presented system is important from the point of view of drug delivery.