Marat O. Gallyamov

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.

Atomic force microscopy examination of tobacco mosaic virus and virion RNA

Atomic force microscopy (AFM) was applied to study uncoated virus particles and RNA prepared by stripping of tobacco mosaic virions (TMV) with mild alkali or urea and dimethylsulfoxide. We found that AFM is an appropriate method to study ribonucleoprotein and free RNA structures. Images of entire tobacco mosaic virions, partially uncoated TMV particles with protruding RNA molecule from one or both ends and individual RNA molecules are presented.

Conformational dynamics of single molecules visualized in real time by scanning force microscopy: macromolecular mobility on a substrate surface in different vapours.

We describe a technique to visualize and effect in real time motion and conformational transitions of single macromolecules. Two steps are involved. First, scanning force microscopy (SFM) was applied to detect in situ conformational transitions of single polymer molecules adsorbed on a substrate surface. Secondly, these changes were induced by controlled variations of environmental conditions in a microscope environmental chamber. In particular, we have revealed that exposure of a substrate with adsorbed macromolecules to vapours of different nature was able to increase molecular mobility and to stimulate conformational transitions of the polymer chains on the surface. Realization of SFM observation in a variable vapour environment was not as difficult as in liquid media. Variations of the vapour composition affected the oscillation dynamics of the cantilever with the scanning probe only to a small extent, and did not impede continuation of the scanning procedure. In fact, the characteristic times of the observed conformational changes were large enough (minutes to dozens of minutes) for sampling images repeatedly. Although recording of an SFM image was slow and required several minutes, we were able to visualize step‐by‐step the successive stages of the slow conformational transformation of the macromolecules adhering to the substrate, i.e. to investigate a molecular response to the environment changes in real time. Here, we studied the reversible collapse–decollapse transitions of cylindrical poly(methacrylate)‐graft‐poly(n‐butyl acrylate) brush‐like macromolecules exposed to different vapours. Single macromolecules on mica tended to assume a compacted globular conformation when exposed to the vapour of compounds, which due to their amphiphilic nature adsorb on mica and lower the surface energy of the substrate (e.g. alcohols). By contrast, the macromolecules adopted extended two‐dimensional worm‐like conformations in the vapours of compounds having high values of surface tension (such as water). In our opinion, the reason for the observed tendency was a competition in spreading on the substrate surface between the macromolecules and the co‐adsorbed vapour molecules. If the brush‐like macromolecules succeeded in the spreading, they acquired an extended conformation. Otherwise they collapsed to globuli in order to reduce the surface area per macromolecule. Thus, the enhanced mobility of synthetic macromolecules on a substrate observed in a vapour environment in combination with the possibility to manipulate the macromolecular conformation via changes in a vapour phase and the ability to visualize the transitions of the macromolecules individually, provides challenging prospects for SFM studies on the dynamics of single molecules under applied external stimuli.

Collagen tissue treated with chitosan solutions in carbonic acid for improved biological prosthetic heart valves

Calcification of bovine pericardium dramatically shortens typical lifetimes of biological prosthetic heart valves and thus precludes their choice for younger patients. The aim of the present work is to demonstrate that the calcification is to be mitigated by means of treatment of bovine pericardium in solutions of chitosan in carbonic acid, i.e. water saturated with carbon dioxide at high pressure. This acidic aqueous fluid unusually combines antimicrobial properties with absolute biocompatibility as far as at normal pressure it decomposes spontaneously and completely into H2O and CO2. Yet, at high pressures it can protonate and dissolve chitosan materials with different degrees of acetylation (in the range of 16-33%, at least) without any further pretreatment. Even exposure of the bovine pericardium in pure carbonic acid solution without chitosan already favours certain reduction in calcification, somewhat improved mechanical properties, complete biocompatibility and evident antimicrobial activity of the treated collagen tissue. The reason may be due to high extraction ability of this peculiar compressed fluidic mixture. Moreover, exposure of the bovine pericardium in solutions of chitosan in carbonic acid introduces even better mechanical properties and highly pronounced antimicrobial activity of the modified collagen tissue against adherence and biofilm formation of relevant Gram-positive and Gram-negative strains. Yet, the most important achievement is the detected dramatic reduction in calcification for such modified collagen tissues in spite of the fact that the amount of the thus introduced chitosan is rather small (typically ca. 1wt.%), which has been reliably detected using original tritium labelling method. We believe that these improved properties are achieved due to particularly deep and uniform impregnation of the collagen matrix with chitosan from its pressurised solutions in carbonic acid.

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.

A biphase H2O/CO2 system as a versatile reaction medium for organic synthesis

We review activity on the usage of a biphase H2O/CO2 system in organic synthesis as a reaction medium of green chemistry. The formation of self-neutralizing carbonic acid in such a system eliminates the problem of salt disposal, typical for acid-catalyzed reactions with the usual mineral and organic acids. A large variety of different reactions to be performed in the biphase H2O/CO2 system are discussed in detail, including cyclization/cycloaddition, hydroformylation, hydrogenation, reduction, coupling, rearrangement, substitution, addition, halogenation, hydrolysis, oxidation and others. These reactions cover a significant part of modern organic synthesis. The main physical properties of carbonic acid being formed in the biphase H2O/CO2 system and their dependence on the temperature and pressure of saturating CO2 are analyzed. The problem with the search for the most optimal reaction conditions from the viewpoint of selection of appropriate pressure and temperature regions for the best yields and selectivity achievable is addressed in general. Comparison with formation and utilization of peroxycarbonic acids, alkylcarbonic acids and carbamic acids by means of saturation with pressurized CO2 of some other biphase systems is discussed in relationship to organic synthesis as well. The influence of a CO2 admixture on the unique properties of high temperature water, another promising green solvent, is also considered.

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.

Scanning Force Microscopy as Applied to Conformational Studies in Macromolecular Research

The modern state of SFM research on polymer nano-objects including single chains is discussed in comparison with other similar high-resolution microscopy techniques. The range of problems to be solved preferentially by SFM is highlighted. Promising methodology to describe quantitatively the morphology of macromolecular objects is proposed. The main benefits of this algorithm seem to be the apparent mathematical correctness as well as the possibility to estimate errors and the confidence of the numbers obtained. Special attention is paid to the dynamic observations of conformational transitions on a substrate in real time regime. This approach allows one to realise direct control of the adsorbed macromolecules by means of exposure to different vapours. Driving forces of the vapour-induced reorganisation are discussed.

Synthesis and properties of fluorinated derivatives of carbosilane dendrimers of high generations

Fluorinated derivatives containing different amounts of fluorocarbon groups in the surface layer of the molecular structure have been synthesized by the chemical modification of a polyallylcarbosilane dendrimer of the sixth generation via hydrosilylation and heterofunctional condensation procedures. The fluorocontaining dendrimers are well soluble in organic solvents and supercritical CO2. Their properties have been studied by DSC, viscometry, dynamic light scattering, and atomic force microscopy.

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.