Biomedical subjects

Sergiy Minko

Publications and source records attributed to Sergiy Minko.

6 recordsLinked to original sources

PubMed2003

Ordered reactive nanomembranes/nanotemplates from thin films of block copolymer supramolecular assembly.

We report on a unique, very simple method of preparation of reactive membranes and nanotemplates with nanoscopic cylindrical channels on the surface of various inorganic and polymeric substrates. Well-ordered nanostructured thin polymer films have been fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-PVP) and 2-(4'-hydroxybenzeneazo)benzoic acid (HABA), consisting of cylindrical nanodomains formed by PVP-HABA associates surrounded by PS. Alignment of the domains has been shown to be switched upon exposure to vapors of different solvents from the parallel to perpendicular orientation to the confining surface and vice versa. The alignment of the cylindrical nanodomains is insensitive to the composition of the confining surface due to the self-adaptive behavior of the supramolecular PVP-HABA assembly. Extraction of HABA with selective solvent results in nanomembranes with a hexagonal lattice (24 nm in the period) of hollow channels of 8 nm in the diameter crossing the membrane from the top to the bottom. The walls of the channels are constituted from reactive PVP chains. The channels were filled with Ni clusters via the electrodeposition method to fabricate the ordered array of metallic nanodots of 1.2 tera per cm(2).

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PubMed2003

Reversible chemical patterning on stimuli-responsive polymer film: environment-responsive lithography.

We report on a novel type of chemical patterning based on thin stimuli-responsive polymer films. The basic concept is the permanent storage (writing) of a pattern, which is reversibly developed and erased upon exposure to appropriate environment, e.g., solvent, pH, and temperature. The smart surface is fabricated from the mixed brush of poly(2-vinylpyridine) and polyisoprene. The mixed brush demonstrates switching behavior upon exposure to different solvents. Cross-linking of polyisoprene via illumination through a photomask results in formation of patterns with suppressed switching. Due to the contrast in switching between illuminated and dark areas, exposure of the smart surface to different solvents causes either reversible formation or erasing of chemical contrast between the illuminated and dark areas. Thus, the pattern surface can very locally attract colloidal particles or can be wetted by water only upon exposure to the special solvent which introduces the contrast between the illuminated and dark areas. Appearance of the patterns indicates particular environment and can be used for local switching of adsorption.

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PubMed2003

Two-level structured self-adaptive surfaces with reversibly tunable properties.

We report a route to fabricate two-level structured self-adaptive surfaces (SAS) of polymer materials. The first level of structure is built by a rough polymer film that consists of needlelike structures of micrometer size. The second level of structure is formed by the nanoscopic self-assembled domains of a demixed polymer brush irreversibly grafted onto the needles. By exposing the surface to solvents that are selective to one of the components of the brush, we reversibly tune the surface properties. The large-scale surface structure amplifies the response and enables us to control wettability, adhesion, and chemical composition of the surface over a wide range.

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PubMed2002

Cascade of coil-globule conformational transitions of single flexible polyelectrolyte molecules in poor solvent.

We show that hydrophobic flexible polyelectrolyte molecules of poly(2-vinylpyridine) and poly(methacryloyloxyethyl dimethylbenzylammonium chloride) are trapped and frozen due to adsorption on the mica surface, and the observed AFM single molecule structures reflect the molecular conformation in solution. An increase of the ionic strength of the solution induces the cascade of abrupt conformational transitions due to the intrachain segregation from elongated coil to compact globule conformations through intermediate pearl necklace-globule conformations with different amounts of beads per chain. The length of the necklaces and the number of beads decrease, while the diameter of beads increases with the increase of ionic strength. Coexistence at the same time of extended coils, necklaces with different amounts of beads, and compact globules indicates the cascade of the first-order-type phase transitions.

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PubMed2002

Mineralization of single flexible polyelectrolyte molecules.

Conformation of a single flexible polyelectrolyte molecule with a hydrophobic backbone in aqueous solution is effected by the interplay of the short-range intramolecular attraction and the long-range Coulomb repulsion. The conformation can be frozen if the molecule is trapped by a solid substrate. With this approach, we prepared the range of single molecule templates from poly(2-vinylpyridine) (P2VP) deposited on the surface of Si-wafer or mica in different conformations from an elongated wormlike coil to compact globule. Pd(+2) was coordinated by P2VP via an ion exchange reaction exposing the samples to palladium acetate acidic aqueous solution. In the next step, Pd(+2) was reduced by dimethylamine borane. This route results in wire-shaped metallic nanoparticle assembles of about 2-5 nm in diameter and 50-700 nm in length. The conformation and size of the underlaying polyelectrolyte molecules determine the dimensions of nanoparticles.

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PubMed2002

Single flexible hydrophobic polyelectrolyte molecules adsorbed on solid substrate: transition between a stretched chain, necklace-like conformation and a globule.

Single flexible polyelectrolyte molecules of poly(2-vinylpyridine) undergo conformational transition from a stretched wormlike coil to a necklace-like globule, and to a compact globule depending on pH and ionic strength in aqueous solution in good agreement with recent theoretical reports. AFM investigations allow the visualization of details of the chain conformation on mica and the extraction of quantitative statistics of molecular dimensions.

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