L. N. Nikitin

Swelling and impregnation of polystyrene using supercritical carbon dioxide

Abstract Swelling of polystyrene (PS) in supercritical carbon dioxide was studied in situ. Experiments were carried out in a high-pressure cell furnished with an optical channel. This allowed to measure the dynamics of diffusion front propagation in the polymer samples during the swelling process by the use of an optical microscope supplied with a digital video camera. The measurements of this dynamics provided information about diffusion coefficients of CO 2 molecules in PS. Diffusion coefficients and equilibrium sorption degrees of the PS samples were also calculated by the use of a gravimetric method. The data were compared with the results of in situ technique. Impregnation of PS films wish ethyl-2-cyano-3(4′-dimethylaminophenyl)acrylate as a model substance for UV-filters and electrographic materials was carried out.

Synthesis of polyimides in supercritical carbon dioxide

High-molecular-mass polyimides were synthesized in the supercritical carbon dioxide by the one-step polycyclization of diamines and tetracarboxylic dianhydrides under batch and flow regimes. The effect of various reaction parameters (including the content of water in the reaction system) on the structure, molecular mass, and yield of polymers was studied. It was shown that the solubility of monomers in supercritical CO 2 is indecisive for polymer growth. It was hypothesized that CO 2 exhibits catalytic activity when polyimides are prepared in the presence of water.

Formation of superhydrophobic surfaces by the deposition of coatings from supercritical carbon dioxide

The deposition of uniform coatings of fluorinated polymers from solutions in supercritical carbon dioxide on a number of rough substrates allowed superhydrophobic (ultrahydrophobic) properties to be imparted to their surfaces, and, namely, to increase the value of the contact angle for water droplet to 150° and greater. The dynamics of changing of geometry of a drying droplet on a substrate is studied. A procedure is developed that permits the penetration of water into the substrate to be detected.

Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide

Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.

Swelling of Polyheteroarylenes in Supercritical Carbon Dioxide

Two series of polyheteroarylenes have been investigated with regard to their physical properties before and after swelling with supercritical carbon dioxide. The study of the dependence of glass transition temperature and free volume of polymers on their conformational rigidity showed that the process of swelling in supercritical carbon dioxide is influenced by the voluminous side groups and by the high boiling solvent N-methylpyrolidinone used for the preparation of the polymers which facilitates the formation of crosslinks or complexes with the macromolecular chains.

Composite materials for medical purposes based on polyvinylpyrrolidone modified with ketoprofen and silver nanoparticles

A method for obtaining composite medical materials based on polyvinylpyrrolidone (PVP K15) modified with ketoprofen in a medium of supercritical carbon dioxide and with Ag nanoparticles prepared by metal vapor synthesis is developed. A system in which ketoprofen and Ag nanoparticles with an average size of ∼16 nm are uniformly distributed over the bulk of PVP is obtained. It is found that the yield of ketoprofen from the composite in the physiological solution is higher than that for an analogous system obtained by mechanical mixing of the components.

Supercritical carbon dioxide: A reactive medium for chemical processes involving fluoropolymers

The application of supercritical carbon dioxide for deposition of fluoropolymer coatings on various substrates and formation of superhydrophobic surfaces and composite core-shell microparticles was discussed.

Fe-containing nanoparticles in siloxane rubber matrices

Polymer-matrix composites consisting of Fe3O4-Fe2O3 and FeCoB nanoparticles in SKTN and SIEL siloxane rubber matrices are synthesized. The introduction of nanoparticles into siloxane oligomers leads to their polymerization, resulting in polymer-matrix nanomaterials. Transmission electron microscopy and small-angle x-ray scattering are used to determine the size of the Fe-containing nanoparticles. The magnetic properties of the nanocomposites are studied by electron magnetic resonance.

Imparting enhanced hydrophobicity to polyester fabrics: Formation of ultrathin water-repelling coatings on the fiber surface

A new technology for hydrophobization of synthetic fiber materials was described. This technological approach is based on formation of nanosized fluoropolymer coatings from solutions of low-molecularweight fraction of ultradispersed polytetrafluoroethylene and tetrafluoroethylene telomers. The mechanism of formation of protective coatings was described, and the properties of polyester materials thus modified were presented.

ULTRAHIGH MOLECULAR WEIGHT POLYETHYLENE MODIFIED WITH SILVER NANOPARTICLES PREPARED BY METAL-VAPOUR SYNTHESIS

Silver‐ultrahigh molecular weight polyethylene nanocomposite prepared by metal‐vapour synthesis has been studied by XPS and TEM.