V. A. Ogarev

Metal Nanoparticles on Polymer Surfaces: 1. A New Method of Determining Glass Transition Temperature of the Surface Layer

New experimental approach allowing to study the structure and properties of polymer surface layers at a nanolevel is proposed. According to this method, metal nanoparticles are first adsorbed on a polymer surface from colloidal solution, then resultant system is stepwise annealed, and the particle embedding in a polymer is examined with atomic force microscope. Potentialities of the method are demonstrated using the gold nanoparticles–polystyrene system (including polystyrene modified with the UV radiation) as an example. It was established that the glass transition temperature of polystyrene surface layer is noticeably lower compared with the bulk value and decreases even more after the UV modification of a polymer surface. Possible use of the results obtained for the solution of other, independent problem, namely for the creation of “two-dimensional” nanocomposites by embedding nanoparticle monolayer ensemble in the surface layer of a glassy polymer at a temperature lower than the glass transition temperature of its bulk is analyzed.

SiO2-based nanocontainers of a novel type: If the template micelles are functional, why remove them

A new method is proposed for creating containers based on mesoporous silica nanoparticles for diverse amphiphilic compounds. The method is based on the use of the micelles of required functional compound (i.e., the compound that is subsequently loaded into the containers) as a template when synthesizing nanoparticles. The prospects and advantages of this approach are exemplified by the synthesis of SiO2 particles using the micelles of cetyltrimethylammonium bromide (which can be used as an inhibitor of hydrogen sulfide corrosion) as a template.

Mesostructured SiO2-based nanocontainers synthesized on a functional template: Capacity and rate of unloading

A new approach to template synthesis of mesostructured pH-sensitive SiO2 nanocontainers is developed. The approach combines the stages of synthesis of the nanocontainers and their loading with a targeted functional substance. The structure, capacity, and the rate of “unloading” of the nanocontainers at different pH values of an aqueous medium under static and quasi-dynamic conditions are studied using mesoporous SiO2 nanoparticles as a model. Nanoparticles are synthesized using the micelles of cetyltrimethylammonium bromide as templates. Based on the obtained information, a mechanism is proposed for release of cetyltrimethylammonium cations from SiO2 nanocontainers into the aqueous medium.

Metal nanoparticles on polymer surfaces: 6. Probing of non-glassy polystyrene surface layer

Peculiarities of the state of the surface layer of the amorphous glassy polymer polystyrene are studied with a specially developed experimental approach. The essence of the method consists in the observation via atomic force microscope for the depth and rate of embedding of gold nanoparticles in a polymer after their preliminary adsorption on the polymer surface from hydrosol. It is shown that the polymer glass-transition temperature near the boundary with air is substantially lowered relative to its bulk value. “Equilibrium” thickness of the non-glassy (“melted”) surface layer is determined through analysis of the data on the kinetics of nanoparticle embedding, and it is revealed that the layer thickness increases with temperature, reaching, near the “bulk” glass-transition temperature, the magnitude that is close to the diameter of the macromolecular coil. The results obtained are analyzed with allowance for published data, and the semi-empirical formula describing variations in the thickness of the non-glassy surface layer as a function of temperature in the interval between the “surface” and “bulk” glass-transition temperatures of a polymer is proposed.

Zinc phthalocyanine-based water-soluble thiolated photosensitizer and its conjugates with gold nanoparticles: Synthesis and spectral properties

A new photosensitizer, monoconjugate of zinc octa-4,5-carboxy-phthalocyanine with L-cysteine, which is rather readily soluble in water, has been synthesized and characterized. The chemisorption of its molecules on the surface of gold nanoparticles with different sizes has been studied. A comparative analysis of the spectral characteristics of the synthesized conjugates of gold nanoparticles with the photosensitizer has shown that the photosensitizer grafted to gold nanoparticles exhibits rather intense fluorescence. Therefore, such conjugates can be used for photodynamic therapy of tumors.

A new method for loading mesoporous silica nanoparticles with drugs: Sol–gel synthesis using drug micelles as a template

It has been shown that mesoporous nanocontainers from SiO2 may be obtained by the sol–gel synthesis using drug (Miramistin) micelles as a template. The nanocontainers resulting from the combination of the stages of their synthesis and loading are characterized by a very high content of the drug (no less than 0.9 g per 1 g of SiO2). The kinetics of Miramistin desorption from the mesoporous particles into an aqueous medium has been studied under static and quasi-dynamic conditions. The desorption has been shown to rather strongly depend on pH. Possible mechanisms of the desorption process have been discussed.

Prospects for increasing the efficiency of water photodecomposition on inorganic semiconductors

The advantages of using hydrogen as a fuel source are discussed, along with the main industrial sources of hydrogen. Recent studies aimed at increasing the efficiency of water photodecomposition on semiconductors in the visible light region using two approaches, doping (alloying) and using metallic nanoparticles and quantum dots, are analyzed.

Silsesquioxane Films on Water Surface

The properties of films formed on the water surface by rigid molecules of organosilicon compounds, oligomeric silsesquioxanes containing phenyl and ethyl side groups, are studied. These compounds are shown to form insoluble stable layers. The properties of the monomolecular films of rigid macromolecules are similar to those of the monolayers of flexible-chain molecules, and the former can be considered as two-dimensional solutions. In contrast to flexible chains, the collapse of the monolayers of rigid molecules, which is formally considered as the first-order phase transition, is accompanied by the formation of an anisotropic lamellar structure, which can be referred to as the mesomorphic state of the substance.

Mesoporous Silica Particles as Nanocontainers for Phthalocyanine Photosensitizers: Estimation of Efficiency in In Vivo Experiments

The template synthesis of mesoporous silica nanoparticles with predetermined size and porous structure is carried out. Water-soluble photosensitizer Photosens is used to study the possibility of applying such particles as containers for photosensitizers of a phthalocyanine series. In vivo experiments have shown that the application of such nanocontainers for the delivery of Photosens to a tumor makes it possible to improve the efficiency of fluorescence diagnostics and the photodynamic therapy of cancer.

Metal nanoparticles on polymer surfaces. 7. The growth kinetics of gold nanoparticles embedded into surface layers of glassy polymers

It has been shown that citrate gold nanoparticles can be embedded (partly immersed) into the surface layers of different glassy polymers with subsequent seeded growth of the particles in an aqueous chloroauric acid–hydroxylamine mixed solution. Quantitative data have been obtained on the seeded growth kinetics, and it has been shown that its rate-limiting stage is the diffusion of metal ions from the bulk solution to the surface of gold nanoparticles.