MEETINGS AND CONFERENCES

CONFERENCE ON THE LIQUID STATE OF MATTER

From May 30 to June 3, 1955, the Second Conference on the Liquid State of Matter, convened by the Kiev State University named after T. G. Shevchenko, was held in Kiev. A considerably larger number of organizations and persons took part in the conference than in the first one (May 1953), and accordingly a broader range of questions related to elucidating the nature of the liquid state was covered.

V. K. Semenchenko presented a report, “Phase Transitions in the Critical and Supercritical Regions,” in which the question of phase transitions above the critical temperature is considered. Proceeding from the thermodynamic conditions of equilibrium and from concepts of a physical boundary of separation, it was shown that below the critical temperature we have a phase transition of the first order, while above the critical temperature there occurs a transition that should be assigned to phase transitions of the second order. The critical point, or more precisely the critical region, is the boundary between two regions—the region in which a first-order phase transition is observed, and the region of second-order phase transitions.

A. Z. Golik, in the report “Structure and Physical Properties of Matter in the Liquid State,” showed that the regularities found earlier in the arrangement of the curves of the temperature dependence of viscosity, compressibility, heat of vaporization, and other properties of liquids possessing a similar structure (Ukr. Khim. Zh. 17, 627 (1951); DAN USSR, No. 1 (1952); ZhFKh 23, 86 (1949)) are closely connected with D. I. Mendeleev’s periodic law. The speaker considered the structurally sensitive properties of liquid elements that in the solid state possess the same lattice and type of bonding, and showed that the curves of the temperature dependence of viscosity, compressibility, heat of vaporization, and other properties of such elements are arranged in a sequence determined by the magnitude of the critical temperature. A connection was shown between the listed properties and the structure of the molecular field. The second part of A. Z. Golik’s report was devoted to an analysis of the results of studies of the physical properties of liquid solutions and their connection with the molecular structure of the latter.

R. F. Mocharnyuk presented the communication “Viscosity and Structure of Solutions of Alcohols and Acids in Acetone.” The viscosity, density, critical temperatures, and latent heats of vaporization of solutions of normal monatomic alcohols and fatty-acid homologues in ace-

tone. It was shown that the arrangement of the viscosity curves is determined by the magnitude of the critical temperature of the solution. The study of viscosity made it possible to estimate the order of magnitude of the interaction between dissimilar molecules in alcohol-acetone solutions. Among the acid-acetone solutions, so-called isoviscous solutions were found—solutions with equal critical temperatures and coincident curves of the temperature dependence of viscosity over the entire investigated temperature interval. On the basis of calculating the apparent molecular volume of acetone dissolved in acids and alcohols, the conclusion is drawn that compression is stronger in acid-acetone solutions than in alcohol-acetone ones. The investigation of the heats of vaporization enabled the author to express certain considerations regarding the mechanism of vaporization of alcohols and acids.

S. D. Ravikovich gave a report on joint work with V. E. Baranovsky and Yu. I. Shimansky on the topic: “Investigation of the heats of vaporization of solutions.” The report presented a new method for studying the latent heats of vaporization of pure liquids and the differential heat of vaporization of solutions. The principle of the method consists in compensation of the Joule heat evolved at the evaporation surface of the liquid, which is caused by the bubbling of air. The report also gave the results of a study of the latent heats of vaporization of binary liquid solutions of various types. It was established that in the case of solutions of liquids analogous in structure, the isotherms are linear if the components of the solution possess similar values of surface tension. In the case of solutions of liquids of different molecular structure, the isotherms assume an S-shaped form. For isotherms of solutions whose components interact strongly with one another, the appearance of extremal points is characteristic. The isotherms of the latent heat of solutions of deuterated alcohols in their normal analogues, as well as solutions of D₂O in ordinary water, have a specific form that does not permit these solutions to be assigned to the class of the simplest physical solutions.

A. F. Skryshevsky reported on joint work with S. D. Ravlikovich: “X-ray investigation of normal alcohols.” In order to elucidate the molecular structure of normal alcohols, the radial distribution function was calculated for methyl, propyl, and butyl alcohols. The X-ray diffraction patterns were obtained at room temperature in monochromatic molybdenum radiation. The radial distribution curves of the alcohols studied in the interval from 0 to 4 Å have two clearly expressed maxima. The first maximum is isolated. For methyl alcohol, the first maximum corresponds to the intramolecular distance \(r = 1.43\) Å and coincides with the generally accepted value of the C—O bond. The second maximum is due to a set of intermolecular distances between OH groups of neighboring molecules, equal to 2.7 Å. For propyl and butyl alcohols, the first maximum on the radial distribution curve is formed as a result of the superposition of two maxima, one of which corresponds to the C—O distance, equal to 1.41 Å. As one passes from one alcohol to another, the area under the first maximum increases, which is explained by an increase in the number of CH₂ groups. The second maximum is formed as a result of the superposition of maxima corresponding to all possible intramolecular distances (with the exception of C—O = 1.41 Å and C—C = 1.62 Å), and also to the distance between OH groups of neighboring molecules. The coordination numbers and mean intermolecular distances for all the alcohols investigated proved to be identical; the radial distribution functions of methyl, ethyl (data of G. Garev), propyl, and butyl alcohols are similar to one another, which is direct confirmation of the similarity of the molecular structure of the indicated alcohols.

G. P. Roshchina reported the results of a study, carried out jointly with M. N. Dadenkova, of the integral intensity of isotropic and anisotropic parts of Rayleigh scattering of light in binary liquid solutions, undertaken with the aim of clarifying the connection between the intensity of scattered light and the molecular structure of the solution. The work used a classification of solutions following from X-ray diffraction data, according to which, in a first approximation, solutions may be divided into molecular-mixed, molecular-nonmixed, and solutions with chemical interaction of the components. The objects of the study chosen were binary solutions of n-alcohols (ethyl and butyl), both with each other and in solvents having, in the liquid state, a molecular structure different from that of the alcohols (glycerin, acetone, benzene, CCl₄, and dioxane). The investigations were carried out in the temperature interval from room temperature to the boiling point. On the basis of the form of the isotherms of isotropic scattering, conclusions were drawn concerning the miscibility or immiscibility of the components of the solution. Among the solutions studied, representatives were encountered of all three of the above-mentioned groups of solutions. Thus, solutions of ethanol in butanol and solutions of butanol in acetone and dioxane belong to molecular-mixed solutions. In solutions of ethanol and butanol in benzene and glycerin, appreciable concentration scattering is observed, which decreases with increasing temperature and, at sufficiently high temperatures, practically disappears. Solutions of ethanol and butanol in CCl₄ are assigned to solutions with chemical interaction of the components.

The authors come to the conclusion that, in general, immiscibility of components is determined by the character of the intermolecular interaction between the unlike particles of the solution and by the intensity of this interaction.

In the report by M. F. Vuks and V. L. Litvinova, “Rotational Mobility of Molecules in Liquids and Solutions and Determination of Their Reorientation Times,” the results are presented of an experimental investigation, by the method of the resonance filter, of the orientational mobility of molecules in a liquid medium and of the determination of the reorientation time of molecules in a liquid.

The work investigated the scattering of light by fluctuations of anisotropy, which appears in the spectrum of scattered light in the form of a broadening of the line or of the formation in it of a so-called wing with monotonically decreasing intensity. The region of the spectrum farther from the center owes its origin to rotational vibrations of the molecules, while the region closest to the center is due to the reorientation of anisotropic molecules. Study of this region of the wing closest to the center can yield valuable information on the rotational mobility of molecules in a liquid medium. Carbon disulfide, benzene, chlorobenzene, bromobenzene, nitrobenzene, benzophenone, and salol were studied at various temperatures from 20 to 200°C, as well as a number of solutions of the indicated substances in CCl₄, cyclohexane, and ether. The investigations showed that reorientation proceeds according to a relaxation law, and the relaxation theory of M. A. Leontovich correctly represents the intensity distribution in the central region of the wing for benzene and carbon disulfide. For the relaxation times, values from \(10^{-12}\) to \(10^{-10}\) sec were obtained (at room temperature). Upon heating the liquid, the relaxation time decreases noticeably, especially strongly for viscous liquids, where this time is large. Dissolution of viscous substances gives the same effect as heating, namely a strong decrease in the relaxation times. From the relaxation time one can judge the character of intermolecular interaction in a one-component liquid or in a solution, and the presence or absence of association.

The report by V. M. Chulanovskii, “Infrared Absorption Spectra of Solutions of Nonelectrolytes,” is based on the work of the author and his collaborators—

MEETINGS AND CONFERENCES

...kov, M. P. Burgova and M. T. Batishcheva. Analysis of the vibrational spectra of nonelectrolyte solutions in various solvents makes it possible to draw conclusions about various effects of a solvent on the frequencies of different vibrations of the molecules of the dissolved substance. A change in the frequency of the valence vibration of a molecule, caused by the influence of neighboring molecules, can be used to characterize the strength of the intermolecular interactions arising in the solution and, in particular, to detect association of various types of formation by molecules of a liquid mixture. The main aim of the work was to clarify the question of the locality or strength of intermolecular bonds in different cases. The formation of associations with a localized bond is reflected in the appearance of a new band, shifted relative to the frequency band of the substance. When the concentration of solutions of CHCl₃ in CS₂ and CHBr₃ in CCl₄ is changed, it was shown that the band shifts continuously—there is no localized bond. In a number of solutions of these same and certain other substances in active solvents, a new band appears, increasing as the concentration decreases and not changing its position in the spectrum—the case of association with a localized bond. Study of changes in various vibrations makes it possible to establish in molecules the atoms or groups that determine the intermolecular bond. The work was carried out on the fundamental tone and the first two overtones of valence and deformation vibrations, which characterize intermolecular interactions in different ways. The speaker presented varied experimental material that makes it possible to assert that bonds of the groups (OH)...(OH) and (OH)...(OCR) differ strongly both in magnitude and in their nature.

O. Ya. Samoilov gave a report on the topic: “Negative hydration of ions in aqueous solutions.”

The speaker notes that hydration of ions in aqueous solutions should be considered not as the binding by ions of some particular number of water molecules of the solution (this is only a special case of hydration), but as the action of ions on the thermal and, above all, on the translational motion of the water molecules nearest to them. This action is characterized by a change in the magnitude of the corresponding potential barriers \((\Delta E)\). The values \(E\) for individual ions can be found from experimental data on the mobility of ions in aqueous solutions and on self-diffusion in water. For a number of ions \(\Delta E > 0\), for others \(\Delta E < 0\)—the water molecules nearest to such ions are more mobile than in pure water. This phenomenon was called negative hydration.

A. Z. Golik devoted his second report to the question of the nature of the “negative” viscosity of electrolyte solutions. The molecular structure of alcohols was studied, and then the density and viscosity of alcoholic solutions of potassium iodide over a wide range of temperatures and concentrations. It was shown that in monatomic alcohols a small compression and an increase in the viscosity of the solution are observed as the salt concentration increases. In solutions of potassium iodide in glycol there was no compression, and on viscosity isotherms at low temperatures a very weakly expressed minimum was observed. In solutions of potassium iodide in glycerine the effect of “negative” viscosity was expressed quite distinctly. Thus it was shown that the effect of “negative” viscosity depends not only on the properties of the ions, but also on the structure of the solvent.

L. A. Kotolenko presented a communication, “Viscosity and Electrical Conductivity of Non-Aqueous Electrolyte Solutions,” based on joint work with A. V. Orishchenko and A. S. Korniristoi. In order to elucidate the connection between the physical properties and the structure of the solvent, the viscosity, electrical conductivity, density, and critical temperatures of solutions of lithium chloride in normal monatomic alcohols and in isoviscous alcohol solutions were studied. It was found that the curves of temperature dependence

viscosity and density are located the higher, the greater the concentration of LiCl and the higher the critical temperature of the solutions (a parameter characterizing intermolecular interaction). The equivalent-electrical-conductivity curves are arranged in the reverse order. The study of the apparent molar volumes of LiCl in alcohols indicates the presence of strong compression, caused both by intermolecular interaction and by the magnitude of the free volume. The use of isoviscous alcohol solutions as solvents made it possible for the authors to distinguish the influence of the electrolyte on the molecules of the solvents.

I. G. Mikhailov delivered a report on the topic: “The velocity of sound and the compressibility of concentrated solutions of strong electrolytes.” The investigation of the compressibility of strong electrolytes makes it possible to obtain important additional data on the structure of water and ionic solutions. The speaker presented the results of measuring the velocity of sound and of calculating the compressibility of 15 aqueous solutions of salts and acids over a wide temperature interval. The concentration dependence of the velocity of sound is determined by the concentration dependence of the compressibility coefficient and of the density. The compressibility coefficient of all the solutions decreases with increasing concentration. This phenomenon is connected with solvation of the ions. In solutions of salts with heavy ions, the density of the solution increases with concentration more rapidly than the compressibility decreases, which leads to a decrease in the velocity of sound as concentration increases. In solutions with light ions, on the contrary, the compressibility decreases more rapidly than the density of the solution increases, and the velocity of sound increases. The velocity of sound in pure water has a maximum at \(t = 70^\circ\) C. Dissolved ions cause a displacement of the temperature maximum toward lower temperatures. Thus, dissolved ions change the structure of water in the same direction as temperature does. The displacement of the temperature maximum of the velocity of sound is connected with the action of the strong field of the ions on the structure of the pure solvent and is not connected with the phenomenon of ion solvation.

I. G. Polotskii presented the results of a study, carried out jointly with Z. L. Khodov, of the velocity of ultrasound and adiabatic compressibility for certain liquids with different types of bonding (toluene, n-butyl alcohol, glycerin, mercury).

The report of E. G. Shvidkovskii was devoted to the influence of insoluble impurities on the viscosity of metallic liquids. Metallic liquids usually contain solid particles (oxides, nitrides; in alloys, crystals of a solid phase may be present). In this connection, the question of the applicability to molten metals of the concept of viscosity in the Newtonian sense is considered. On the basis of rheological considerations it is shown that, practically always, the absorption of energy during the flow of a metallic liquid can be characterized by the Newtonian concept of viscosity. Discussion of experimental data on the viscosity of molten aluminum and silicon shows that in this case the influence of insoluble impurities (oxides, nitrides) has a hydrodynamic nature, and the magnitude of the effect may considerably exceed the influence on the viscosity of aluminum of the addition of another component—silicon. In other cases, however, the influence of insoluble impurities on the viscosity of a molten metal may have a much more complex molecular nature. This is indicated by the precrystallization branching of viscosity upon supercooling (Vestnik MGU, No. 9, p. 63 (1953)), the viscosity hysteresis of molten metals (Vestnik MGU, No. 5, p. 159 (1951)), and others. These phenomena are associated with the process of structural rearrangement in the liquid phase that prepares crystallization (Vestnik MGU, No. 12, p. 43 (1950); No. 2, p. 57 (1954)).

G. I. Goryaga presented a report on the mechanism of transport phenomena in liquids. Proceeding from generally accepted ideas about the nature of thermal motion in liquids and relying on the ideas of Ya. I. Frenkel, A. I. Bachinskii, and others, the author arrives at exponential expressions for the transport coefficients. In these formulas the activation energy is proportional to the latent heat of vaporization and inversely proportional to the coordination number. From the equations obtained by the speaker follow the formulas of A. I. Bachinskii, Andrade, and A. S. Predvoditelev. The author’s approximate formulas are in satisfactory agreement with experiment.

N. K. Rakova presented the results of a study of the electrical conductivity of bismuth, lead, and tin in the solid and liquid states. It was shown that the electrical conductivity, for example, of polycrystalline bismuth is determined mainly by the values of the electrical conductivity of a single crystal in the direction along the principal crystallographic axis and perpendicular to it. Insoluble impurities have a noticeable influence on the course of the temperature dependence of the electrical conductivity of bismuth in the solid state. Melting of bismuth under conditions of slight superheating above the melting point (\(10^\circ\)C) does not affect the arrangement of the crystallographic axes in a bismuth single crystal. As a result, apparently, in liquid bismuth, with slight superheating above the melting point, traces of the single-crystal structure are preserved. More considerable superheating (\(40^\circ\)C) changes the initial orientation. For the metallic liquids investigated, the transition from the normal to the supercooled state is not associated with such a change in the structure of short-range order as would affect the character of the temperature dependence of electrical conductivity. The character of the temperature dependence of the electrical conductivity in liquid bismuth and tin gives reason to suppose that, in the region \(500\text{–}550^\circ\)C, structural transformations occur in these metals.

The report of A. R. Regel was devoted to certain features of the temperature dependence of the electrical conductivity of liquid metals of the second group of D. I. Mendeleev’s table. If, for metals of the first group, the temperature coefficient of electrical resistance is the same in the solid and liquid states, then for metals of the second group it is generally small and regularly changes from negative values for Mg to small positive values for Hg.

Earlier the author had proposed that this effect is connected with a change in the structure of short-range order in melts. Heating leads to the destruction of elements of anisotropy in the short-range order that existed in the solid phase, and, beginning at some high temperature, the resistance of metals of the second group should increase rapidly, since thermal motion and the loosening of the structure become the determining factors in the increase in resistance. In order to verify the considerations set forth and experimentally determine the temperature range in which the temperature coefficient of resistance for Zn and Cd is small, measurements were carried out up to \(1200^\circ\)C, i.e., above the boiling point. It was shown that, for Zn and Cd, there does indeed occur a strong increase in the temperature dependence of their resistance. Moreover, their temperature coefficient of resistance is small over a very large temperature interval. The temperature dependence of the specific resistance of gallium and antimony is qualitatively similar to the dependences for zinc and cadmium, only less sharply expressed. The examples cited illustrate the connection between the electrical resistance of liquid metals and changes in their structure. The observed temperature dependence of electrical resistance agrees well with the results of A. Z. Golik, who related the structural changes of liquid metals of the second group to their viscosity.

MEETINGS AND CONFERENCES

B. V. Deryagin presented a report, “The influence of dissolved substances on the viscosity and properties of boundary phases,” based on joint work with V. V. Karasev.

The speaker described in detail improvements introduced into the previously developed “blowing method,” which make it possible to measure the thicknesses of liquid films during the blowing process itself, and also set forth the results of studies of pure liquids and solutions. In a number of cases, on graphs depicting the velocity profile in a blown film of a solution, substantial deviations are observed from the straight line characteristic of pure vaseline oil. These deviations occur at comparatively large distances from the solid wall, sometimes reaching \(10^{-5}\) cm. At present it is still difficult to give an exhaustive explanation of all the observed phenomena; however, from the data presented it is clear that a solid wall is capable of producing changes in the viscosity of adjacent layers of liquid. Apparently, these changes are caused by one or another orientation of the liquid molecules.

V. A. Kizel reported on the results of studying the structure of the surface of a liquid by measuring the degree of ellipticity of the polarization of light reflected from the surface. This effect is due to the existence of a surface layer differing in its properties from the liquid in the bulk. The author developed a method for measuring the magnitude \(\rho\) and its dependence on temperature. The magnitude \(\rho\) was measured on an open surface for 60 liquids; in doing so, a regular change of the magnitude \(\rho\) in homologous series was established. It was shown that the effect is determined by the individual properties of the liquid. A strong dependence of \(\rho\) on temperature was established. On approaching the solidification point, an increase of \(\rho\) is observed in all cases without exception. A connection between this phenomenon and the course of crystallization of the liquid is demonstrated. Far from the solidification point, for liquids with anisotropic molecules, a decrease in \(\rho\) is observed with increasing temperature. The steepness of the decrease is connected with the parameter of correlation of molecular orientation, on the basis of which the author considers molecular orientation in the surface layer to be one of the causes of the investigated effect. The presence, in liquids with isotropic molecules, of considerable ellipticity independent of temperature far from the solidification point indicates the existence of other causes of this effect as well.

A. E. Lutsky gave a report on the topic: “Molecular constants and the boiling temperature of liquids.” The report presents a method for establishing a relation between the properties of molecules and the microparticles composing them. The method is illustrated by the study of boiling temperatures of liquids. It is shown that the boiling temperature does not depend on the mass and size of molecules; however, as a rule, it is proportional to the polarizability of the molecules to the power \(1/2\), and changes linearly with increasing dipole moment of the molecules. For a large number of molecules with the same molecular shape,

\[ (T_k)_{p\phi} = \alpha^{1/2}(\mathrm{const} + \mathrm{const}\ \mu), \]

where \(T_k\) is the boiling temperature, \(p\) is pressure, \(\phi\) is shape, \(\alpha\) is polarizability, and \(\mu\) is the dipole moment. The influence of the shape of molecules on \(T_k\) is considered. These regularities make it possible to explain the character of the change of \(T_k\) in various series of chemical compounds, as well as of the elements (groups zero and seven).

S. S. Dukhin delivered a report, “On the continuity of the properties of liquids in the supercooled state.” The speaker showed that a number of carefully studied physical properties of supercooled molecular

liquids, such as viscosity, heat capacity, etc., show abrupt changes at certain temperatures (for example, at the crystallization temperature). At the same time, in the behavior of the density and of some other physical properties, no peculiarities are observed at the same temperatures. In the speaker’s opinion, the explanation of the results obtained should be sought in a jump-like change in short-range order at the indicated temperature points.

The participants in the Conference approved the general plan and directions of the studies being carried out and expressed the wish that work on the study of the liquid state be coordinated, and that both experimental and theoretical studies of pure liquids and liquid solutions be expanded. A decision was adopted to publish the proceedings of the Conference. The next All-Union Conference on the liquid state of matter is scheduled for 1957.

G. P. Roshchina, N. A. Ryndin, Yu. I. Shimanskii