Modelling a flow of a highly viscous liquid with the boundary layer of low viscosity in an extruder

Features of the flow of a highly viscous liquid in an extruder with boundary layer of low viscosity liquid at the cylinder wall and at the endless screw surface are considered. The liquid flow is modeled under conditions of isothermal simple shift using cylindrical model of a screw canal. The profiles of rates for the stream of a highly viscous liquid with the ring boundary layer of low-viscous liquid at the cylinder wall and at screw in the both presence and absence of a counter pressure are calculated. Consideration of computer calculations shows that increase in the flow rate is possible when the counter pressure tends to zero and the low-viscous liquid forms a ring boundary layer at the cylinder wall.     

Effect of the range of repulsions on the existence of a stable liquid phase

Experimental and theoretical results have established that the range of the attraction plays a critical role in determining whether a particle system exhibits a stable liquid phase. Changes to the range of the repulsions can similarly affect the existence of a stable liquid phase; however, these effects have not been clearly elucidated. We demonstrate that an increase in the range of repulsions can either enhance or decrease the stability of the liquid phase, depending on the form of the interaction potential. For either case, the critical variable that controls the stability of the liquid phase is the ratio of the representative energies of the liquid and solid phases.     

Additivity of the dynamic curvature of a thermocapillary depression and static curvature of a wetting meniscus

A thermocapillary depression is induced by a laser beam in a layer of a transparent liquid on an absorbing substrate. Two plane-parallel wettable plates are immersed in the liquid in symmetrical positions with respect to the point of incidence of the beam on the liquid. The diameters of the thermocapillary response formed by the laser beam on a screen are studied in their dependence on the curvature of the equilibrium liquid meniscus formed between the plates. The property of additivity is experimentally proved; according to this property, the curvature of the free liquid surface is equal to the algebraic sum of the static curvature of the wetting meniscus and the dynamic curvature of the thermocapillary depression.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 259–267.Original Russian Text Copyright © 2005 by Tarasov.     

Effect of molecular structure of a dichroic dye and the ordering of a liquid crystal on the dichroism of the dye-liquid crystal binary mixtures

The orientational ordering of dyes doped into liquid crystals has been investigated. The experimental results show that the ordering of the dyes can be expressed as a function of the order parameter of the liquid crystal host and the molecular structure of the dye. In addition a theory of the ordering of molecules in a binary mixture system has been derived by extending Kimura's theory. The validity of the theory has been confirmed by comparison with the experimental results using various combination of azo dyes and liquid crystals.     

Effect of molecular structure of a dichroic dye and the ordering of a liquid crystal on the dichroism of the dye-liquid crystal binary mixtures

The orientational ordering of dyes doped into liquid crystals has been investigated. The experimental results show that the ordering of the dyes can be expressed as a function of the order parameter of the liquid crystal host and the molecular structure of the dye. In addition a theory of the ordering of molecules in a binary mixture system has been derived by extending Kimura's theory. The validity of the theory has been confirmed by comparison with the experimental results using various combination of azo dyes and liquid crystals.     

On the Flow of a Viscous Liquid around a Heated Spheroidal Particle

An expression is derived for the viscous drag of a spheroidal particle whose temperature differs from that of the carrier liquid. Calculations are performed for the case where the temperature dependence of the liquid viscosity may be represented by an exponential power series.     

The influence of electric field-induced orientation on the retraction of a liquid crystal droplet immersed in a flexible polymer matrix

We measured the apparent interfacial tension between a liquid crystal and a flexible polymer by deformed droplet retraction method. An external electric field is applied to change the director orientation in liquid crystal droplet. The deformation and recovery of a single liquid crystal droplet dispersed in a polydimethylsiloxane (PDMS) matrix were realized by a transient shear flow and observed by polarized optical microscope. In order to control the director orientation in LC droplet, the electric field is applied perpendicular and parallel to the flow field, respectively. The different orientation induced by electric field in liquid crystal droplet has different behavior during droplet retraction and affect the apparent interfacial tension between liquid crystal and flexible polymer.     

Biooxidation of a synthetic waste by a microbial film grown on the liquid surface in a shallow flow reactor

A new process of biological waste treatment was developed by use of microbial films grown on the liquid surface in a shallow flow reactor. The performance of this process was tested using a synthetic waste that contained acetic acid as a model organic pollutant. About 90% of acetic acid (10,000 mg/L-1) in the synthetic waste was removed by setting alpha tau: (alpha specific liquid surface area, cm-1, and tau: hydraulic liquid detention time, h) higher than 15 cm-1/h. It was necessary to maintain alpha large enough (more than 10 cm-1 in most cases) to satisfy oxygen demand for the biooxidation. The oxygen balance and TOC determinations showed that the acetic acid removed was completely oxidized with oxygen transferred through the liquid surface. This process would contribute to energy savings, since it requires no forced aeration for oxygen supply.     

The dielectric constant of a polar liquid by the simulation of microscopic drops

We report a new method of computing the static dielectric constant for a polar liquid using a natural system, a drop of liquid in its own vapour. Results for the Stockmayer potential agree with those computed for a homogeneous “cyclic” liquid with Ewald corrections. The method is quite general.     

A molecular beam study of the evaporation of water from a liquid jet

A method to maintain a clean surface of a liquid in a high vacuum is described. Using a very thin and fast liquid jet it is not only possible to prevent freezing of the liquid but also to reduce the number of collisions between evaporating molecules to negligibly small values. Thus many of the standard, vacuum dependent, particle probing techniques for solid surfaces can be used for studies of rapidly vaporizing, high vapor pressure liquids. In a first molecular beam investigation we have used time-of-flight analysis to measure the velocity distribution of H₂O molecules vaporizing from thin jets of pure liquid water. The experiments were carried out for liquid jet diameters between 50 and 5 µm. In this range the expanding vapor is observed to undergo the transition to the collision-free molecular flow regime. From the measured velocity distributions the local surface temperature is determined to be less than 210 K. This appears to be the lowest temperature ever reported for supercooled liquid water.     

Molecular view of the isothermal transformation of a stable glass to a liquid

We have used neutron reflectivity to measure translational motion on the nanometer length scale in exceptionally stable glasses of tris(naphthylbenzene). These glasses are prepared by vapor deposition onto a substrate held somewhat below the glass transition temperature (T(g) = 342 K). When the most stable samples are annealed at 345 K, no translational motion is observed on the 12 nm length scale for over 10,000 s and full mixing requires more than 60,000 s. For comparison, the equilibrium supercooled liquid mixes in 1000 s at this temperature and on this length scale. These measurements provide insight into the mechanism by which a stable glass transforms into a liquid. "Melting" of the stable glass appears to occur by the growth of liquid regions into the surrounding glassy matrix, perhaps by a surface-initiated growth process. At 345 K, translational motion in the stable glass is at least 100 times slower than motion in the supercooled liquid.     

Dynamics near a liquid-liquid phase transition in a non-tetrahedral liquid: the case of gallium

We use molecular simulation to analyze liquid dynamics in the vicinity of the liquid-liquid phase transition (LLPT) recently discovered in the modified embedded-atom model for elemental gallium. For this purpose we analyze the diffusive behavior in terms of the mean-squared displacement and self-intermediate scattering functions for two systems obtained by cooling the stable liquid through the LLPT at different cooling rates. The results show a pronounced heterogeneity of the dynamics upon the onset of the LLPT. Furthermore, it is found that this heterogeneity is closely correlated to the structural properties of the 9-fold coordinated high-density and 8-fold coordinated low-density liquid forms involved in the transition, showing a mixture of domains with very different diffusion time scales. The dynamics of the low-density liquid is found to be much more sluggish than that of the high-density form. Analysis of the energetics suggests that the origin of this difference is rooted in the fact that the cohesion in the former is significantly stronger than that in the latter.     

Scaling analysis of a charged jet formed upon electrospinning of a viscoelastic liquid

The dependences of the parameters of a jet and the intensity of the current generated in it during electrospinning of a viscoelastic liquid on the conductivity, viscosity, surface tension, and other characteristics of the liquid, as well as the strength of an external electric field and the liquid flow rate, are considered. The process is described in terms of the Maxwell liquid model, which is characterized by a single relaxation time and convective-type nonlinearity. Two regimes corresponding to high and low liquid flow rates are identified. The jet diameter is shown to decrease with a rise in the liquid conductivity coefficient and electric field strength. Moreover, at high flow rates, the current intensity almost linearly grows with the field strength.     

Second order of perturbation theory correction to the radial distribution function of a liquid with the interaction potential of hard spheres plus a square-well

A liquid with the interaction potential of hard spheres plus a square-well is analyzed using the Monte-Carlo technique. Numerical results for the perturbation theory series over a square-well potential are obtained in the form of the Barker and Henderson discrete representation. Approximating expressions for the correction to a liquid radial distribution function in the second order of perturbation theory are presented. The obtained results allow us to define this correction with a root-mean-square deviation of about 0.007. It is shown that the given approach provides a complete calculation in the second order of perturbation theory, and also the determination of the third order correction to the free energy for a liquid interacting with the potential of the Lennard-Jones type.     

Mechanisms of the Diffusion of Nonpolar Substances in a Hydrophilic Ionic Liquid

The structural-dynamic features of ionic liquid-nonpolar substance systems are studied by means of molecular dynamics using Frenkel’s fundamental theory of a liquid and the phonon theory of the thermodynamics of a liquid, in combination with the DL_POLY_4.05 software package. Argon, methane, and benzene molecules serve as the dissolved substances. Model concepts are proposed and analyzed to describe the diffusion of molecules of a dissolved substance in an ionic liquid. It is shown that an increase in the mass of the molecules of a dissolved nonpolar substance correlates with their mobility in a hydrophilic ionic liquid (IL). This determines the diffusion of the components of dmim⁺/Cl^? IL solutions and is responsible for the anomalous behavior of the solubility of nonpolar substances in them.     

Identification of the individual polychlorinated biphenyls in a mixture by gas-liquid chromatography.

Retention indices were computed for all of the 210 possible chlorinated biphenyls on 13 gas chromatographic liquid phases. All possible pairwise comparisons of retention indices were made for each liquid phase, each pair of liquid phases and each set of three liquid phases. On the basis of a closeness criterion of 10 (deltaRI = RIa - RIb = 10), those combinations of three or fewer liquid phases which could distinguish between nearly all possible pairs of chlorinated biphenyls were selected. Further considerations such as column efficiencies, analysis time required, resolution achievable and availability led to the selection of several common liquid phases for the qualitative and, in some cases, quantitative analysis of the individual components of mixtures of polychlorinated biphenyls. A few specific applications are discussed.     

Calculating the surface tension between a flat solid and a liquid: a theoretical and computer simulation study of three topologically different methods

We discuss three topologically different methods for calculating the surface tension between a flat solid and a liquid from theoretical and computer simulation viewpoints. The first method, commonly used in experiments, measures the contact angle at which a static droplet of liquid rests on a solid surface. We present a new analysis algorithm for this method and explore the effects of line tension on the contact angle. The second method, commonly used computer simulations, uses the pressure tensor through the virial in a system where a thick, infinitely extended slab of liquid rests on a solid surface. The third method, which is original to this paper and is closest to the thermodynamic definition of surface tension, applies to a spherical solid in contact with liquid in which the flat solid is recovered by extrapolating the sphere radius to infinity. We find that the second and third methods agree with each other, while the first method systematically underestimates surface tension values.     

Influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate: a sum frequency generation analysis

Sum frequency generation spectroscopy (SFG) was used to study the influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The orientation of the cation at the gas-liquid interface was analyzed as a function of ionic liquid concentration in water for concentrations from 0 to 1 mole fraction of the ionic liquid. The cation was found to be oriented with the imidazolium ring nearly parallel to the surface plane with a tilt angle > or = 70 degrees when the ionic liquid was dry. Furthermore, no noticeable change in the orientation was observed when high concentrations of water were mixed with the ionic liquid. The cation butyl chain is projecting into the gas phase with a CH(3) tilt angle of 54 +/- 2 degrees when the ionic liquid is dry and 46 +/- 4 degrees when mixed with water. Water is oriented at the surface only for concentration < or = 0.02 mole fraction of the ionic liquid. At higher ionic liquid concentrations (mole fractions > or = 0.05) the gas-liquid interface resembles that of the pure ionic liquid.     

Microdosing on Evaporation from the Surface of a Porous Solid

The processes are examined that occur when dilute gas mixtures are prepared by the evaporation of a solution of impurities in an indifferent liquid solvent from the surface of a porous solid. Relationships between the concentrations of the impurities in the liquid and gas phases are given.     

Study of the Effect of an Antifoaming Agent on the Evaporation of the Components During the Stirring of a Coating Dispersion Containing a Volatile Agent

The main objective of this work was to evaluate the evaporation of coating liquids containing a volatile component (ethanol) and an aqueous polymer dispersion under well‐controlled circumstances. The influence of different concentrations of a polydimethylsiloxane type antifoaming agent was studied. In consequence of to its low interfacial tension, it can form a layer on the surface of a liquid, and the effect of this was studied by determination of the quantity of the stirred liquid that was evaporated. The effects of different operational factors were compared by means of factorial designs. It was conluded that the presence of ethanol in the liquid changed not only the extents of the effects of the factors, but also their relative importance as concerns the evaporation process. The highest difference in effect of a given factor was detected for the stirring rate, while the lowest difference was observed for the duration of stirring. A high concentration of Dimeticon decreased the extent of evaporation, but not significantly. Thus, the alterations in the effects of the operational factors were not very substantial either. It may be stated that this antifoaming agent does not result in a relevant change in the evaporation in these systems containing ethanol as a volatile component. Accordingly, primarily the operational parameters must be considered during the formulation of these compositions. This information helps towards the design of an appropriate stirring device, because our results indicate that open systems are not adequate and it is known that hermetically closed tanks make atomization impossible. Hence, determination of the critical control points of coatings with a liquid containing a volatile component cannot be avoided because the vapour of such materials can be very dangerous.