V. M. Rudoy

Unusual wetting dynamics of aqueous surfactant solutions on polymer surfaces

Static and dynamic contact angles of aqueous solutions of three surfactants--anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C(12)E(5))--were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid-vapor interface. Obviously, another process involving adsorption at the expanding solid-liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.

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.

Effect of Gold Nanoparticles on Mouse Spermatogenesis

The response of the mouse male germ cells exposed to gold nanoparticles (∼2.5 nm) was studied. Our investigation demonstrates that treatment with Au nanoparticles for four days does not impair the architecture of the spermatogenic epithelium. Cytogenetic evaluation using micronucleus assay showed that gold nanoparticles can affect the chromosomes of early primary spermatocytes. However, gold nanoparticles did not induce chromosome abnormalities in spermatogonial stem cells. Further, the cauda epididymal sperm was isolated on the 14th day after treatment and was incubated in SDS solution (Na dodecyl sulphate) and then in a solution containing DTT (dithiothreitol) to induce nuclear chromatin decondensation. Observations showed that after four days of treatment of spermiogenic (postmeiotic) cells with gold nanoparticles the decondensation process had no differences from the control. On the contrary, in the experiment with the same cells and period of fixation but with a single exposure to gold nanoparticles, the number of mature gametes with totally decondensed nuclei reached 100% as opposed to 44% in the controls.

Bovine sperm chromatin is not protected from the effects of ultrasmall gold nanoparticles

The response of ejaculated bovine spermatozoa to gold nanoparticles was studied by the standard method of nuclear chromatin decondensation in vitro. After the treatment of semen samples with a hydrosol containing gold nanoparticles with an average diameter of ∼3.0 nm and a concentration of 1 × 1015 particles/mL, the ability of sperm nuclei to decondense in the presence of sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) dramatically changed compared to the control. The frequencies of gametes with nondecondensed (“intact”), partially decondensed, and completely decondensed nuclei correlated as 40: 32: 28% and 0: 36: 64% in the experiment and the control, respectively. Moreover, the appearance of a sufficiently large number of gametes with destructed and almost completely destroyed nuclei was noticed in the spermatozoa treated with gold nanoparticles. This article suggests the putative mechanisms of action of ultrasmall gold nanoparticles on the structural and functional integrity of the deoxyribonucleoprotein (DNP) complex of mature male gametes.

Determination of polarity parameters for glass fibres by inverse gas chromatography: Some results and remarks

Glass fibres of various surface properties (sized and unsized ones) have been investigated in this work by means of inverse gas chromatography (IGC) at infinite dilution conditions in the 30-100°C temperature range. The conclusion is made that the IGC method is too sensitive to give an unambiguous description of the complex character of heterogeneous glass fibres. Possible reasons are discussed with a critical consideration of our own results and the corresponding literature data. The polarity parameters have been calculated by means of various theoretical approaches. It was found that the polarity parameters based on topological indices, according to Brendlé and Papirer, were able to describe more correctly the Lewis acid-base surface characteristics than previous approaches.

Colloidal synthesis of new silver-based nanostructures with tailored localized surface plasmon resonance

Silver-based nanostructures with tailored localized surface plasmon resonance are of interest for a number of practical applications. They can conventionally be divided into three main groups: (1) anisotropic silver particles, (2) particles of alloys of silver with other metals, and (3) composite particles with dielectric or magnetic cores and silver shells. Fine “tuning” of plasmon resonance of these particles is ensured by changes in their shapes, composition, and/or structure. Procedures for the colloidal synthesis of nanostructures of all these groups and some fields of their application are described, with the main attention focused on core/shell composite particles.

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.

Comparative study of the properties of silver hydrosols prepared by “citrate” and “citrate-sulfate” procedures

Comparative study of the properties of silver hydrosols prepared with the use of two classical procedures (“citrate” and “citrate-sulfate”) is performed. The possibility of using these procedures for the synthesis of stable monodisperse silver hydrosols with particle diameters of 20 nm and more is studied. The effect of the main parameters of synthesis (the ratio of initial components, the rate of their mixing, etc) on the hydrosol characteristics is investigated. It is revealed that, in the case of “citrate” synthesis, it is quite impossible to realize conditions ensuring the reproducible preparation of colloidal solutions with particles having sufficiently uniform size and shape. The procedure for the one-stage preparation of “citrate-sulfate” hydrosol (without multiple precipitation-redispersion of nanoparticles) is elaborated and it is shown that the thus prepared hydrosol is greatly superior in both the optical characteristics and the morphological uniformity of particles to the citrate sol. An increase in synthesis temperature to 100°C leads to a substantial enhancement of the stability of colloidal solution. The possibility of using “citrate-sulfate” hydrosol for the design of two-dimensional ensembles of silver nanoparticles on the quartz and silicon surfaces modified with poly(2-vinylpyridine) is demonstrated. It is shown that such ensembles possess optical properties that allow to use them in designing “two-dimensional” polymer-metal nanocomposites potentially suitable for using as active media in devices working on the principle of surface plasmon resonance.

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.

The effect of ozone on plasmon absorption of gold hydrosols. Quasi-metal and metal nanoparticles

The character of the interaction between ultrasmall gold nanoparticles and ozone is shown to be mainly governed by the particle structure. For borohydride sols of gold nanoparticles with sizes of ≈3 nm, which are characterized by metallic properties, this interaction is reduced to reversible adsorption of ozone on their surface. At the same time, ozone adsorption on “nonplasmon” Au particles that have a diameter of 2 nm and a very defective structure results in their irreversible structural rearrangement and transition to a metallic state, which is accompanied by the appearance of a surface plasmon resonance. The set of the results obtained shows that nanoparticles of borohydride gold sols are more efficient as possible hemosensors of ozone than are larger particles synthesized by the citrate method.