Andriy Voronov

Mechanism of Silver Ion Reduction in Concentrated Solutions of Amphiphilic Invertible Polyesters in Nonpolar Solvent at Room Temperature

Fast formation and efficient stabilization of silver nanoparticles from [Ag(NH3)2]OH are achieved in concentrated nonpolar solutions of amphiphilic invertible polyesters based on poly(ethylene oxide) (PEO) and aliphatic dicarboxylic acids. Surface-modified silver nanoparticles able to be dispersed in both a polar and nonpolar medium are developed in the form of a ready-to-use colloidal solution with an enhanced silver concentration. The PEO fragments of polyesters form cavities (also called pseudo-crown ester structures) that can bind metal ions. The reduction of bound metal ions proceeds via oxidation of polyoxyethylene fragments. No chemical reducing agents are necessary in this approach. The polyesters act simultaneously as an efficient reducing agent and stabilizer. The main focus of the present research is to clarify the chemical mechanism of silver ion reduction in amphiphilic polyester solutions. A one-electron reduction mechanism is proposed to explain the formation of silver nanoparticles. The effect of the poly(ethylene oxide) fragment length and the polyester concentration are explored by examining several amphiphilic polyesters.

Encapsulation of fillers with grafted polymers for model composites

Glass beads were encapsulated by grafted polymers : polybutylacrylate and polystyrene. Grafting was performed by the polymerization initiated from the particle surface with preliminary adsorbed polyperoxide initiator. Grafting procedure and properties of grafted film were studied using model substrates : powders, plates, and wafers by wetting technique and SEM. Conditions of grafting affect the film structure. They are porous, and due to some sort of pores the wetting liquid is able to penetrate into covering and reach the substrate. Model epoxy composites were prepared with covered glass beads. The coverings allowed a decrease of adhesion between the matrix and bead surface to detect acoustic emission caused by the debonding process. The dependence of debonding stress from covering the structure and nature was studied.

Highly Efficient Phase Boundary Biocatalysis with Enzymogel Nanoparticles

The enzymogel nanoparticle made of a magnetic core and polymer brush shell demonstrates a novel type of remote controlled phase-boundary biocatalysis that involves remotely directed binding to and engulfing insoluble substrates, high mobility, and stability of the catalytic centers. The mobile enzymes reside in the polymer brush scaffold and shuttle between the enzymogel interior and surface of the engulfed substrate in the bioconversion process. Biocatalytic activity of the mobile enzymes is preserved in the enzymogel while the brush-like architecture favors the efficient interfacial interaction when the enzymogel spreads over the substrate and extends substantially the reaction area as compared with rigid particles.

Invertible micellar polymer assemblies for delivery of poorly water-soluble drugs.

Strategically designed amphiphilic invertible polymers (AIPs) are capable of (i) self-assembling into invertible micellar assemblies (IMAs) in response to changes in polarity of environment, polymer concentration, and structure, (ii) accommodating (solubilizing) substances that are otherwise insoluble in water, and (iii) inverting their molecular conformation in response to changes in the polarity of the local environment. The unique ability of AIPs to invert the molecular conformation depending on the polarity of the environment can be a decisive factor in establishing the novel stimuli-responsive mechanism of solubilized drug release that is induced just in response to a change in the polarity of the environment. The IMA capability to solubilize lipophilic drugs and deliver and release the cargo molecules by conformational inversion of polymer macromolecules in response to a change of the polarity of the environment was demonstrated by loading IMA with a phytochemical drug, curcumin. It was demonstrated that four sets of micellar vehicles based on different AIPs were capable of delivering the curcumin from water to an organic medium (1-octanol) by means of unique mechanism: AIP conformational inversion in response to changing polarity from polar to nonpolar. The IMAs are shown to be nontoxic against human cells up to a concentration of 10 mg/L. On the other hand, the curcumin-loaded IMAs are cytotoxic to breast carcinoma cells at this concentration, which confirms the potential of IMA-based vehicles in controlled delivery of poorly water-soluble drug candidates and release by means of this novel stimuli-responsive mechanism.

Reactive Hydrogel Networks for the Fabrication of Metal–Polymer Nanocomposites

In this study, highly stable gold and silver nanoparticles evenly distributed within a crosslinked poly(acrylamide)/poly(N-(hydroxymethyl)acrylamide) (PAAm-PHMAAm) network have been fabricated without addition of a reducing agent. Remarkably, the same chemical hydrogel composition has been involved in the successful fabrication of spherical gold and silver nanoparticles within the hydrogel template. The hydrogel network acts simultaneously as an efficient reducing agent and stabilizer. The PAAm-PHMAAm hydrogel network binds metal ions and, following reduction of bound to crosslinked template metal ions, proceeds via oxidation of hydroxymethyl hydrogel fragments. A one-electron mechanism is proposed for the formation of the silver and gold nanoparticles.

Hierarchical Micellar Structures from Amphiphilic Invertible Polyesters : 1H NMR Spectroscopic Study

The environment-dependent behavior of invertible polyesters has been studied by 1H NMR spectroscopy. In dilute toluene solutions, the micelle exterior is made up of the lipophilic fragments, and the interior consists of the hydrophilic constituents. The polyester inverts the structure in an aqueous medium to form micelles with a hydrophobic inner part and a hydrophilic outer part. Increasing polyester concentration leads to the formation of hierarchical structures both in toluene and in an aqueous medium as a result of the aggregation of unimolecular micelles and the formation of hydrophilic and lipophilic domains. On the contrary, no unimolecular micelles or micellar aggregation has been observed in acetone or chloroform.

Interfacial micellar phase transfer using amphiphilic invertible polymers

Micelles formed from new amphiphilic invertible polymers (AIPs) can sequester hydrophobic molecules in water and transfer their payload to a non-polar phase. The amount of material transferred depends primarily on micellar loading capacity. Increasing the lipophilicity of the AIP composition increases the amount of material transferred. The obtained data indicate that AIPs have the potential to serve as an alternative for administration of polymer-based nanopharmaceuticals. Invertible polymeric micelles can potentially facilitate controlled release of poorly water-soluble agents incorporated within the micellar interior when compared to release by thermodynamically stable conventional (non-invertible) micelles.

Investigation of craze development using small-angle X-ray scattering of synchrotron radiation

Abstract The development of crazes in polycarbonate was investigated with the method of ultra-small-angle X-ray scattering (USAXS) of synchrotron radiation. Measurements at different temperatures and with different draw rates were carried out. The two-dimensional scattering patterns were analyzed by means of a fibrillar model of the craze. The geometrical parameters of the craze as a function of the macroscopic draw ratio were determined by using a curve-fitting procedure. From the measured values of the diameter and the mean distance of the fibrils, it is possible to calculate the volume fraction vf of the fibrils directly. Additional scattering caused by submicrocracks is discussed.

Effect of polyacrylate binding layers on adhesion of UV-cured epoxyacrylate protective coatings on optical fibers

Polymer coatings on optical fibers were made of homopolymers of methyl methacrylate, poly(butyl acrylate) and poly(nonyl acrylate), the random copolymer of methyl methacrylate with 5% of methacrylic acid and asymmetric block copolymers of the same acrylates with short polar block of poly(5-tert-butyl-peroxy-5-methyl-1-hexen-3-yne-co-maleic anhydride) (50 : 50 mol %). They were obtained by means of physisorption of the polymers from the solution on the surface of two sorts of fused silica rods and plates preliminary heated at 200 and 900°C. The contact angle method was employed to evaluate the structure of adsorbed polymer films in the conditions of poor solvent. The fraction of the silica surface capped by the polymer, and surface free energy and its polar and dispersive components were estimated. The results were correlated with the data of adhesion tests between covered silica rods and ultraviolet (UV)-cured epoxyacrylate and discussed in terms of interpenetration of chains of the preliminary adsorbed polymer and polymer matrix. The chains of binding layer (adsorbed polymer) pull-out from the matrix and pull-off from the substrate failure mechanisms were suggested to explain the adhesion data for different sorts of silica rods. The efficiency of the polymer binding layer increases in the following order: asymmetric block copolymer < copolymer < homopolymer.

Amphiphilic invertible polymers for adsolubilization on hydrophilic and hydrophobized silica nanoparticles

Adsolubilization of poorly water-soluble 2-naphthol into amphiphilic invertible polymers (AIPs) has been successfully performed on hydrophilic and hydrophobized silica nanoparticles. The polymers adsolubilize molecules of sparingly water-soluble 2-naphthol into the adsorbed layer on both substrates. AIP macromolecules show different surface activity depending on length of the hydrophobic fragment in macromolecules. Different AIP fragments are responsible for polymer adsorption on hydrophilic and hydrophobized silica. It is expected that mainly AIP hydrophobic fragments interact with 2-naphthol molecules and facilitate adsolubilization. The amount of adsolubilized 2-naphthol does not depend on substrate nature and length of the hydrophobic fragment in polymer. It is primarily regulated by the total length of the adsorbed macromolecules.