Vol 81, No 4 (2019)

We present a review of theoretical studies dealing with the statistical thermodynamics of water-in-oil (w/o) microemulsions and application thereof for the synthesis of nanoparticles. The general theory of composition fluctuations in reverse micelles has been described. For w/o microemulsions based on ionic surfactants, a model has been formulated, which enables one to explain the experimentally observed spherical shape of reverse micelles, to calculate the enthalpy of water solubilization and the chemical potentials of water and surfactants, and to plot the phase diagrams of the microemulsions. Two models that explain limitation of nanoparticle growth in w/o microemulsions have been described, namely, a thermodynamic model, which is based on the search for the minimum free energy of a nanoparticle-containing microemulsion, and a kinetic model based on the consideration of the coagulation activation energy of nanoparticles as depending on their sizes and the water-to-surfactant molar ratio.

Homogeneous nucleation of supersaturated antimony vapor has been studied in a laminar-flow chamber with the use of transmission electron microscopy, diffusion spectrometer of aerosols, supersaturation cutoff, laser light scattering, and other methods. Surface tension σ_s of a critical nucleus and radius R_s of its surface of tension have been determined from the experimentally measured temperature field by numerical simulation of the processes occurring in the chamber. The calculation results are in good agreement with the measured profile of a deposit on chamber walls, the average size and concentration of formed aggregates, the average size of primary particles, and their number in an aggregate. Equivalent volume V_eq = 0.87 cm³ of the zone of intense nucleation, average nucleation rate I = 5 × 10¹⁰ cm⁻³ s⁻¹, average supersaturation S₄ = 3.2 × 10⁶, average temperature T = 421 K in this zone, and radius R_s = 0.63 nm and surface tension σ_s = 220 mN/m of critical nuclei formed in this zone have been calculated. The surface tension of antimony nuclei has appeared to be lower than the surface tension of its planar surface by 46%. In our previous works, it was found that the surface tension of critical bismuth nuclei was, on the contrary, markedly higher than that of its planar surface. Different signs of the deviation from the surface tension of a planar surface have, for the first time, been observed for elements of the same group.

The development of the sensing systems based on the ultrathin films of functional metal organic networks as efficient synthetic alternative to molecular biosensors is in the focus of intense research. Herein we report how to fabricate uniformly structured surface-attached metal organic frameworks (SURMOFs) from zinc complex of meso-carboxyphenyl-substituted porphyrin and zinc acetate as films on the surface of self-assembled monolayers of silanes and thiols. The layer-by-layer self-assembly with shortened time of the layer deposition at room temperature was applied to obtain 5-layer SURMOFs with high crystallinity, which was confirmed by X-ray diffraction. These SAM-supported SURMOF films were used as sensing layers for qualitative response to organic molecules in aqueous solutions. By using surface plasmon resonance spectroscopy, we showed that the SURMOFs do not bind 4-nitrophenol and uracil whereas they are capable of absorption of purine compounds such as adenine and adenosine 5-monophosphate. This binding is a size sensitive process in favor to adenine suggesting the effect of the SURMOF structure on the molecular recognition. The UV-vis spectroscopy study of the process indicated that the recognition of purines by the porphyrin-based SURMOF proceeds through the interactions of the amine groups with zinc ions in metal clusters rather than with the central metal ions in porphyrin cores. Our findings provide an insight into the sensing properties of the porphyrin-based SURMOFs that is useful for further advancements in fabrication of responsive thin films for biologically relevant analytes.

The solubilization of a water-insoluble biologically active compound, curcumin, in micelles of amphiphilic antimicrobial agents, such as miramistin, ethonium, and cetalkonium, is investigated, and the thermodynamic characteristics of this process are determined. It has been shown that the sol–gel synthesis of multifunctional mesoporous silica containers can be realized using these surfactants’ micelles, which contain solubilized curcumin, as “hybrid” templates.

S,N-derivatives of alkylhydrazines, including 1,1-dimethylhydrazine, have been synthesized for the quantitative analysis of trace impurities of hydrazines in environmental objects. The molecular-statistical method has been used to calculate the thermodynamic characteristics of their adsorption on graphitic thermal carbon black. The dependences of the thermodynamic functions of S,N-derivatives of alkylhydrazines on their molecular mass and stereochemical features of hydrocarbon radicals have been found. The results have been compared with experimental data obtained by liquid chromatography when studying the interaction of S,N-derivatives of 1,1-dimethylhydrazine with Hypercarb graphitic carbon sorbent.

The permeability of polyelectrolyte capsule shells is controlled by incorporating a natural hydrophobic pigment, haematin, into them via adsorption from an aqueous ammonia solution. The modification of capsules with the dye has been confirmed by the data of Raman light scattering and the measurements of the ζ potential. The capsules containing haematin in the shells have been characterized by spectrophotometry, atomic force microscopy, and scanning electron microscopy. Time variations in the surface charge, morphology, and thickness of the capsule shells have been discovered. Moreover, a decrease in the permeability of the modified capsule shells with respect to rhodamine 6G has been revealed. Polyelectrolyte capsules containing doxorubicin inside of them and haematin in their shells have been obtained. It has been shown that the drug is not spontaneously released into an aqueous medium over time.

In the current investigation, a new insight into the adsorptive interaction of iron–silicon mixed oxide with arsenate was proposed through comparative studying the behavior of arsenate on the mixed oxide and on the parent oxides, i.e., iron hydroxide and silica. All the oxides were characterized by using different physiochemical methods. The arsenate concentration, pH, temperature, co-ion effect, and calcination of adsorbents were the key parameters of this investigation. The Langmuir model was used for the interpretation of the adsorption data. The thermodynamic parameters and spectroscopic evidences of the samples before and after arsenate adsorption confirmed that the mechanisms of arsenate adsorption by Fe(OH)₃ and mixed oxide showed close similarity.

Molecular dynamics is employed to study the structure of a nanofluid prepared from liquid argon and aluminum nanoparticles with sizes below 4 nm. The parameters of the potential of interatomic interaction of a nanoparticle are varied to determine their influence on the structuring of the basic fluid not only in the vicinity of the aluminum particles. Particle volume concentration is varied from 0 to 5%. The radial distribution function of basic liquid molecules at nanoparticle surface is calculated. It is shown that the presence of the particles in the nanofluid causes additional ordering of basic fluid molecules. In particular, the first maximum in the radial distribution function increases by three to five times, while the characteristic size of the short-range order zone grows. The characteristics of the short-range order of the basic fluid in a nanofluid are governed by the parameters of the interaction potential of nanoparticle atoms. An increase in the effective diameter and the depth of the potential well for the interaction of the nanoparticle-composing atoms enhances the structuring of the nanofluid.