Determination of the critical parameters of polymer solutions

The contribution of short-range orientation order to the chemical potentials of components in a polymer-solvent system was determined. The temperature dependence of the degree of orientation of solvent molecules relative to polymer chains in a polyisobutylene-benzene system was obtained. It was shown that the short-range order in the polymer-solvent system fails with temperature to a much lesser extent than in the pure solvent. The expressions for the upper and lower critical solution temperatures with allowance for the contribution of short-range order to the entropy and the free energy of solution, as well as to the chemical potentials of components, were found. It was demonstrated that, in the polymer-solvent system, two upper and two lower critical solution temperatures can exist.     

Determination of the chemical potential using energy-biased sampling

An energy-biased method to evaluate ensemble averages requiring test-particle insertion is presented. The method is based on biasing the sampling within the subdomains of the test-particle configurational space with energies smaller than a given value freely assigned. These energy wells are located via unbiased random insertion over the whole configurational space and are sampled using the so-called Hit-and-Run algorithm, which uniformly samples compact regions of any shape immersed in a space of arbitrary dimensions. Because the bias is defined in terms of the energy landscape it can be exactly corrected to obtain the unbiased distribution. The test-particle energy distribution is then combined with the Bennett relation for the evaluation of the chemical potential. We apply this protocol to a system with relatively small probability of low-energy test-particle insertion, liquid argon at high density and low temperature, and show that the energy-biased Bennett method is around five times more efficient than the standard Bennett method. A similar performance gain is observed in the reconstruction of the energy distribution.     

Approximate solutions of the Bloch-McConnell equations for two-site chemical exchange.

Approximate formulas for the transverse-relaxation rate constant and resonance frequency have been derived for nuclear spins subject to two-site chemical exchange. The new results are more accurate than previous approximations when chemical exchange does not approach the fast-exchange limit or when site populations are not highly asymmetric. Results are derived from an effective average evolution operator that contains contributions from both exact eigenvalues of the Bloch-McConnell equations. These expressions are useful for interpretation of chemical exchange processes in NMR spectroscopy.     

Determination of solutions density by the dilatometric titration method

A new approach to the determination of solutions density based on dilatometric titration data was developed. The results of testing this method by the example of dilution of a sodium chloride solution are presented. The method allows density of solutions to be determined with a high accuracy (±1×10^?5 g cm^?3) in a wide concentration range in the course of a single experiment.     

Epitaxial chemical deposition of ZnO nanocolumns from NaOH solutions

A new method of depositing expitaxial ZnO nanocolumns on sputter-coated ZnO substrates is described that utilizes supersaturated zincate species in sodium hydroxide solutions and requires no complexing agents. Uniform arrays of columns are grown reproducibly over entire substrates in 10-50 min. Columns are 50-2000 nm long and 50-100 nm wide. Strict substrate cleaning and/or preparation was not necessary with this method, in contrast to many other techniques, probably because the high pH generates a reproducible surface. The interfacial properties of the substrate are critical to lowering the activation energy for columnar growth; therefore films grow only on substrates precoated with ZnO, not on bare glass or ITO- or SnO2-coated glass. Factors affecting the column growth are elucidated, and experimental observations are correlated with crystal growth theory.     

Solubility of monazite chemical components in humic acid solutions

The α-factor is a measure of the epithermal neutron flux deviation from the ideal distribution 1/E, where E is neutron energy. It defends on the position of the irradiation channel in reactor. A determination method of the α-factors in irradiation channels of Dalat reactor is presented by fitting the epithermal neutron spectrum obtained from the calculation using MCNP code. The fitting α-values were compared to those by experiment used the “Cd-ratio” method with monitors ¹⁹⁷Au–⁹⁴Zr and ¹⁹⁷Au–⁶⁴Zn. It shows that the α-values calculated from neutron spectra agree well with experimental ones. The difference between both data is about 6%.     

Influence of the hydrotrope structure on the physical chemical properties of polyoxide aqueous solutions

The physical chemical properties of block substituted poly(ethylene oxide-propylene oxide) (PEO-PPO) block copolymer aqueous solutions were evaluated in the presence of two hydrotropes of different structures: sodium p-toluene sulfonate (NaPTS) and butyl monoglycol sodium sulfonate (NaBMGS). The critical micelle concentration and the cloud point of the copolymer solutions were displaced to higher concentration values, indicating that the solubility of the copolymer was increased in the presence of the hydrotropes. Temperature increased the micelle hydrodynamic radius, but concentration had a limited effect. Carbon-13 nuclear magnetic resonance (13C NMR) permitted the interaction between the surface-active agent and the hydrotrope to be evaluated: NaBMGS, which presented a more pronounced hydrotropic effect, interacts more effectively with the hydrophobic moiety of the surfactant, while NaPTS interacts rather mainly with the hydrophilic oxyethylenic groups. The results furnish experimental evidence to conclude that the hydrotropic phenomenon is specific in relation to both the hydrotrope and the solubilizate.     

Mechanism of chemical deposition of nickel-boron coatings in tartrate-glycine solutions

The effect of glycine additive on the deposition of nickel-boron coatings from tartrate-glycine solutions was studied.     

Determination of activity coefficients of binary adsorption solutions

Conclusions A method was prepared for calculating the activity coefficients of the components of adsorption solutions from specified curves, corresponding to constant values of the integral of the Gibbs equation, when binary gas mixtures are adsorbed on microporous adsorbents.Translated from Izvestiya Akademiya Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 166–168, January, 1972.     

Determination of traces of perchlorate in chlorate solutions

Perchlorate present in chlorate solutions is determined gravimetrically as tetraphenylphosphonium perchlorate after destruction of chlorate by addition of hydrochloric acid. Interference of Fe(III) and Cr(III) is prevented by complexing with tarartic acid. Replicate analyses of a sodium chlorate solution containing NaClO(3), NaCl, Na(2)Cr(2)O(7), and 390 ppm NaClO(4) showed 405 ppm NaClO(4) (standard deviation 19 ppm, 12 results).     

Determination of caloric quantities of dilute liquid solutions

This article reviews recent advances in the experimental determination of caloric quantities, for instance heat capacities, of dilute liquid nonelectrolyte solutions. Direct methods, i.e. calorimetric methods, as well as indirect methods, i.e. vapor-liquid equilibrium studies as a function of temperature, are considered.     

Determination of the absolute specific conductance of primary standard KCl solutions

A determination of the absolute specific conductance of KCl solutions is demonstrated. The measurement is based on the conductance cell with a well defined geometry, having a difference in the removable center tube of accurately measured dimensions. The specific conductance of the solution is obtained from the measured resistances of the cell with and without the center tube and the measured l/A ratio of the center tube. Specific conductances obtained using the cell agree with the previously accepted standards for 0.1 demal and 0.01 demal solutions within 0.02%. Results are also presented for solutions based on molality. The temperature control, bridge, and detector technology used to obtain results of this accuracy are described.     

Radiation chemical oxidation of hydrazine in aqueous solutions containing oxygen

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, p. 1192, May, 1988.     

Quantitative chemical analysis of electrolytes in aqueous solutions exploiting the Donnan dialysis process

Chemical analysis of electrolytes in aqueous solutions is performed with a dialyzer consisting of two selective membranes: a cation and an anion-exchange membrane. The dialyzer actually functions like a galvanic cell when dialysis is carried out. The current that appears in the cell is measured. Since the dialysis process is caused by the concentration gradient, the current measured also depends on the concentration gradient. For proper conditions, it becomes possible to determine the concentration. The method may compete in some aspects with ion-selective potentiometry. The text was submitted by the authors in English.     

Determination of free acidity in antimony chloride solutions

A method for the determination of free acid in antimony(III) chloride solutions is described. The total acid is determined by titration in the presence of tartrate as masking agent, and the bound acidity is calculated from the antimony content of the same aliquot, determined by titration with bromate. This method is simple and rapid compared to the earlier potentiometric techniques.