I. R. Nasimova

Microgels for the Encapsulation and Stimulus-Responsive Release of Molecules with Distinct Polarities

A microfluidic strategy for the encapsulation and stimulus-responsive release of molecules with distinct polarities from the interior of microgels is reported. The approach relies on (i) the generation of a primary O/W emulsion by the ultrasonication method, (ii) MF emulsification of the primary emulsion, and (iii) photopolymerization of the monomer present in the aqueous phase of the droplets, thereby transforming them into microgels. Non-polar molecules are dissolved in oil droplets embedded in the microgels. Polar molecules are physically associated with the hydrogel network. Upon heating, the microgels contract and release polar and non-polar cargo molecules. The approach paves the way for stimuli-responsive vehicles for multiple drug delivery.

Self-Oscillatory Systems Based on Polymer Gels

Chemical and mechanical oscillations arising when the Belousov-Zhabotinsky reaction is performed in composite gels based on polyacrylamide and silica gel and gels of poly(acrylamide-co-sodium acrylate) have been investigated. The catalyst of the reaction can be incorporated into a gel through electrostatic interactions. Mechanical and absorption properties of polymer matrices are characterized, and the periods and amplitudes of mechanical oscillations arising in them are estimated. The mechanism of the phenomenon under consideration is advanced.

Chemomechanical oscillations in polymer gels: Effect of the size of samples

The appearance of chemomechanical oscillations in polymer gels during the Belousov-Zhabotinskii reaction is studied. The effect of the size of composite gels based on polyacrylamide and silica, as well as the gels of acrylamide-sodium acrylate copolymer, on the mode of the reaction and the period of oscillations is examined. It is established that there is a limiting gel diameter below which the chemical oscillations of the oxidation state of a catalyst do not result in the appearance of chemical waves: Redox transformations occur uniformly within the sample. The gel-size threshold value below which the mechanical oscillations of the polymer network are not observed is determined. On the basis of the comparison of phase difference between mechanical and chemical oscillations for samples of various sizes and data on the swelling degree of gel in equilibrium states in which the catalyst is in either the oxidized or the reduced state, a conclusion is made about the mechanism of volume oscillations of the polymer network.

Novel pH-responsive hydrogels with gradient charge distribution

A strategy for the preparation of smart polymer gels with gradient weak polyacid distribution that exhibit pH-induced bending/straightening behaviour is reported. Gradient distribution of acid units inside the gel sample is obtained by copolymerization of N-isopropylacrylamide with acrylic acid sodium salt between two surfaces with different degrees of hydrophobicity/hydrophilicity. The reversibility of pH-induced bending is demonstrated.

Effect of ionization on the temperature- and pressure-induced phase transitions of poly(N-isopropylacrylamide) gels.

The ionization effects on the pressure-induced phase transition of weakly charged poly(N-isopropylacrylamide-co-acrylic acid) (PNIPA-AAc) gels have been investigated by small-angle neutron scattering. At low temperature, T, and pressure, P, the structure factor of PNIPA-AAc gels was well represented by a Lorentzian (L) function, which was similar to noncharged PNIPA gels. However, at high Ps, the contribution of inhomogeneities became large and a squared-Lorentzian term had to be added in addition to the L term. At high Ts, on the other hand, a scattering maximum appeared, indicating microphase separation. This scattering maximum was suppressed by increasing P up to P approximately 100 MPa and then reincreased at higher Ps. The following facts were disclosed: (1) The peak position and height were very sensitive to P, which is mainly ascribed to strong pressure dependence of hydrophobic interaction, (2) ionization leads to microphase separation at elevated temperatures, (3) the re-entrant phase behavior is commonly observed in the P-T plane due to the parabolic variation of the polymer-solvent interaction with P, and (4) the pressure and temperature dependence of the structure factor was reproduced with the Rabin-Panyukov theory and was interpreted with a convexity of hydrophobic interaction with respect to pressure.

Homophase and heterophase polymerizations of butyl acrylate mediated by poly(acrylic acid) as a reversible addition–fragmentation chain-transfer agent

The radical polymerization of n-butyl acrylate in organic, aqueous, and water–alcohol media in the presence of poly(acrylic acid) containing a trithiocarbonate group within the chain is studied for the first time. It is shown that in nonselective solvents (1,4-dioxane and DMF) poly(acrylic acid) serves as a reversible addition–fragmentation chain-transfer agent and the triblock copolymer poly(acrylic acid)–block–poly(n-butyl acrylate)-–block-poly(acrylic acid) is formed. In aqueous and aqueous–organic media (under conditions of emulsion, dispersion, and miniemulsion polymerizations as well as polymerization-induced selfassembly), the block copolymer being formed additionally serves as a stabilizer of polymer–monomer particles. The sizes of these particles and the molecular-mass characteristics of the resulting polymers may be controlled via variation in the concentration ratio of the components. It is found that, during polymerization in aqueous media, there is the formation of spherical polymer particles that preserve their morphology in thin films prepared via precipitation of the synthesized dispersion.

Effect of polyelectrolytes on aggregation of a cyanine dye

The effect of poly(acrylic acid) and poly(methacrylic acid) on the molecular state of a cationic cyanine dye (3,3′-diethyl-2,2′-thiacarbocyanine iodide) was studied. Gels based on the above polymers were shown to efficiently absorb an oppositely charged dye. The absorption of dye ions by a gel induced their aggregation. It was shown that, in the acrylic acid-based gels, H-aggregates, dimers, and single ions of the dye coexist. In gels containing methacrylic acid units, dye ions mainly formed H-aggregates. A comparison of aggregation of dye ions in the gels with that in aqueous solutions of corresponding polyelectrolytes was performed. When dye ions were immobilized in a gel network, the proportion of the ions forming the H-aggregates was considerably larger than that in solutions. The effect of the gel network charge density on the aggregation of dye ions was investigated. It was shown that an increase in the fraction of charged units in network chains facilitates aggregation.

Structure Formation and Nonlinear Dynamics in Polyelectrolyte Responsive Gels

General principles of information processing by chemical lightsensitive reaction—diffusion media are discussed. New modes of image evolution in the process of its transformation by reaction—diffusion medium are proposed. New approach for the design of materials that are capable to exhibit oscillating swelling-deswelling behaviour based on complexes of catalyst of Belousov—Zhabotinsky (BZ) reaction with polymer gels is described.