Vol 86, No 4 (2024)

Magneto-rheological polishing technology is widely used in the processing of high-precision optical elements. One of the determining factors in magnetorheological polishing technology is the nature and quality of the nanoabrasive in the composition of the magnetorheological suspension. In this study, a method has been developed for the sol-gel synthesis of amorphous silicon dioxide nanospheres used as a nanoabrasive for magnetorheological polishing of water-soluble crystals used for the manufacture of nonlinear optical elements of laser technology. The technical result was achieved by introducing synthesized silicon dioxide nanoabrasive into the composition of the magnetorheological suspension. The physicochemical characteristics of the resulting nanoabrasive are presented. The results of electron microscopy confirm the spherical morphology of SiO₂ particles, and a particle size distribution varying in the range of 40–60 nm has been established, which ensures the uniformity and quality of surface treatment of optical elements with a magnetorheological suspension. The structural properties of SiO₂ nanoabrasive were studied by X-ray powder diffraction. The introduction of SiO₂ nanoabrasive into the magnetorheological suspension made it possible to achieve high quality processing and surface cleanliness, and also ensured final polishing of the surface of KDP single crystals to a roughness value of no more than 6 Å. The results of the work are of interest for optimizing the process and improving the technology of magnetorheological polishing.

Gold, nickel and platinum nanoparticles were synthesized by impregnating the monocrystalline silicon surface with precursors (an aqueous solution of the corresponding salt). The morphology of formed nanostructured coatings has been studied, the electronic structure and adsorption properties of synthesized nanoparticles with respect to H₂, O₂, and H₂O have been determined. It was found that oxidized nickel nanoparticles are reduced by molecular hydrogen, and unalloyed platinum nanoparticles are oxidized by molecular oxygen already at room temperature, which is not observed for particles deposited in a similar way on highly oriented pyrolytic graphite. We also found that the formation of water molecules on gold nanoparticles in interaction with H₂ and O₂ proceeds in two stages, unlike the three-stage process (sequential exposure in H₂, O₂, H₂) which is characteristic of nanoparticles deposited on graphite. Differences in the adsorption properties of nanoparticles of the same type deposited on graphite and silicon are associated with the adsorption of a significant amount of test gases on the latter.

Three samples of magnetic fluid based on magnetite particles stabilized by a double layer of surfactant in water were synthesized. To stabilize the samples, lauric, oleic acids and their salts were used in three different combinations. The viscosity of the synthesized samples was measured as a function of concentration, temperature, and shear rate. With increasing temperature, the viscosity of a liquid sample stabilized by a double layer of lauric acid does not decrease relative to the viscosity of water, as was previously observed for classical magnetic fluids, but increases. For a sample stabilized by two layers of lauric and oleic acids, the temperature dependence of relative viscosity is non-monotonic. The relative viscosity of a sample stabilized with a double layer of oleic acid is practically independent of temperature.

To determine the concentration of the samples, measurements of magnetization curves were carried out, followed by their granulometric analysis. It has been established that the dispersed composition of the samples remains unchanged when diluted. The initial susceptibility of liquid samples was found to increase more slowly with increasing concentration than predicted by the modified effective field model. In contrast to the MEP model (and not only it), the coefficient of the quadratic term in the expansion of the initial susceptibility in the Langevin susceptibility series turned out to be significantly less than 1/3. Thus, to describe the properties of magnetic fluids stabilized with a double layer of surfactants, the construction of new theories of dipole-dipole interaction of particles is required.

It has been shown that the colloidal system Pd(Acac)₂–mod–H₂, where mod are chiral stabilizers of molecular (8S,9R)-cinhonidine, (-)-Сin, and ionic type (-)-Cin*HCl and (-)- Cin*2HCl, exhibits catalytic activity in the asymmetric hydrogenation of N-acetyl-α-amidocinnamic acid (AACA) at room temperature and a H₂ pressure of 5 atm.

In the presence of protonated forms of cinchonidine, the esterification reaction of the product N-acetylphenylalanine (N-APha) was observed. The excess of the R-(-)-enantiomer of N-acetylphenylalanine reaches 78% on the Pd(Acac)₂–(-)-Сin–H₂ system at the ratio (-)-Сin/Pd = 1.5, while the protonated forms of the quinine alkaloid as modifiers of catalytic systems show less efficiency with respect to chiral induction.

Using XRD and HR-TEM, the formation of palladium nanoparticles with average size 5.3 ± 0.8 nm and 4.2 ± 0.5 nm, respectively, was established for the systems Pd(Acac)₂–(-)-Cin–H₂ and Pd(Acac)₂–(-) -Сin *HCl–H₂.

The micellization of polyoxyethylated alkylphenols Triton X-100 (TX-100) and Triton X-114 (TX-114), which belong to nonionic surfactants, was studied in aqueous solutions using the spectrophotometric method. The spectral characteristics of the absorption curves of surfactant solutions were calculated in the concentration ranges: 0.02–0.80 mmol/L for TX-100 and 0.02-0.40 mmol/L for TX-114. The influence of the scanning step along the wavelength scale (0.1, 0.2, 0.5 and 1.0 nm) on the position of the maxima and absorption intensity was studied. It was found that the optical density increases monotonically over the entire concentration range. It was revealed that at all scanning steps there is a bathochromic shift in the absorption maximum of the long-wave band (275 nm) by 1.5 nm (TX-114) and 2.0 nm (TX-100) at a certain surfactant concentration. A characteristic kink is observed in the curve of the dependence of the position of the absorption maximum on the surfactant concentration, the position of which depends on the scanning step. A new method for the spectrophotometric determination of the CMC of TX-100 and TX-114 is proposed, based on establishing the dependence of the position of the absorption maximum of the long-wave band in the electronic absorption spectrum on the surfactant concentration in an aqueous solution. It was found that for graphical determination of CMC, the optimal scanning step is 0.1 nm. The CMC values for TX-100 and TX-114 were determined, which were (0.24 ± 0.02) mmol/L and (0.20 ± 0.01) mmol/L, respectively, consistent with the literature data.