Experimental and theoretical study of the displacement process between two electrolyte solutions in a microchannel

Displacement of one electrolyte solution by another in a microchannel is required in many biolab chip devices. The objective of this paper is to develop a better understanding of the displacement process between two electrolyte solutions under an applied electric field in a cylindrical microchannel in terms of the traveling distance of the interface between these two electrolyte solutions. In order to develop a general model to predict the location of the interface, two different situations are considered; one model assumes the presence of a sharp interface between the two solutions and the other model considers a mixing zone between the two solutions. Carefully conducted experiments were carried out to obtain the current-time relationship, which is used in the model to predict the location of the interface. In these experiments, deionized ultrafiltered water (DIUF water), 10 mM KCl, 0.1 mM KCl, and 0.1 mM LaCl3 solutions were used as the testing liquids. Polyamide-coated silica capillary tubes of internal diameter 100 mum and length 10 cm were employed in this study. The relationship between traveled distance of the interface and time was predicted by a developed model based on the measured current-time relationship for such a displacement process under a constant applied electric field. The characteristics of the nonlinear change of the traveling distance with the time were also discussed in this paper.     

Ultimate high-frequency conductivity of solvent and electroconductivity of electrolyte solutions

The temperature curves of the ultimate high-frequency electroconductivity of water and acetonitrile were analyzed. The temperature curves of specific electroconductivity of aqueous 0.1 M sodium chloride solution and acetonitrile 0.1 M 1-butyl-3-methylimidazol trifluoromethane sulfonate were compared. The electroconductivity activation energy of solutions was found coinciding with the ultimate high-frequency electroconductivity activation energy of solvents within the experimental error. The specific electroconductivity of solutions was shown to increase at higher temperature in direct proportion to the ultimate high-frequency electroconductivity of solvents.     

A view of electrolyte solutions

The uncertainties in the route to infinite dilution for 2–2 electrolytes are discussed in relation to the practical difficulties of determining the standard emf's of simple reversible cells containing ZnSO₄ in H₂O and D₂O solutions. These difficulties are due to uncertainties in the theory of highly charged ions in aqueous solution. Recent developments in theories of electrolytes, especially those for which numerical results are available, are critically evaluated for their accuracy and adaptability to changes in the solute potential. Simple refinements to the model (i.e., the solute potential) are described, and the changes are interpreted, in terms of the molecular interactions between sets or pairs of ions in the pure solvent. Recent work on the effect of solvent granularity and other molecular properties of the solvent (e.g., dipole moment) on the solute potential is reviewed.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

A new theory of electric conductivity

This theory proposes that electric conductivity, metallic or otherwise, ohmic or superconducting, is simply the result of electron density moving through atomic and molecular orbital overlaps in material bodies. The theory argues that electron density moves without resistance (is superconducting) while it is contained within extended quantum mechanical (QM) states which are constructed so that the electron wave function does not experience reflections at any interface. The theory states that ohmic conduction results when the electron wave function does experience reflections at QM interfaces, and requires the continuous external application of electromotive force (EMF) to overcome those reflections and maintain an electric current.     

A study of a nonprimitive model for electrolyte solutions based on perturbation theory

The equation for the Helmholtz free energy for systems of small anisotropic molecules and ions is deduced by substituting the complete expression for various potential energies (including repulsive, dispersive, electrostatic, and induced energies) into the perturbation expansion. The equation is applied to pure water. The relative dielectric constant is set at unity. Based on the equal chemical potentials of equilibrated vapor and liquid phases, the molecular parameters of water are regressed from the densities of saturated vapor in the temperature range of 0 to 370°C. The ARD of regression is 1.16%. These parameters are used to predict the heat of vaporization and densities of saturated vapor and liquid phases of water in the same temperature range. The ARDs of prediction are 4.5% and 9.8%, respectively. The equation is used to correlate the osmotic coefficients of twelve 1:1 electrolyte solutions. The relative dielectric constant is set at unity. The parameters (Soft-sphere diameter and dispersive constant) of seven ions (Na⁺, K⁺, Rb⁺, Cs⁺, Cl^–, Br^–, and I^–) are obtained. The total average absolute deviation between calculated and experimental values of the osmotic coefficient is 0.041. The parameters of ions can keep constant in different systems.     

Repulsive interface forces in overlapping electric double layers in electrolyte solutions

The historical development of the problem of the electric interaction of particles in electrolyte solutions is comprehensively discussed. The existing approaches are divided into force-based methods, where the mechanical (ponderomotive) forces of the electric field are directly calculated, and energy-based methods calculating the free energy of the colloid system (at least the part of the free energy which is determined by the repulsive forces of electrical nature). The fundamental works of Langmuir, Derjaguin, Levine, Verwey and Overbeek are discussed in detail. At the same time, new original methods are proposed: the method of effective displacements; the formula of free energy of overlapping double layers.Special attention is paid to the analysis of electrostriction forces in liquids, particularly in electric double layers. The non-contradictory application of the concepts of classic macroelectrostatics is shown to result in the need to take into account electrostriction forces in overlapping double layers. The main formulas are given for force and energy of repulsion in flat surfaces with a constant density of the electric charge on them. These formulas are derived with electrostriction forces taken into account. A number of the theoretical results are new.Some experiments are discussed in measuring repulsive forces in colloid systems. A qualitative agreement is established between the experimental results of Ottewill et al. and the theory of electrostriction forces in double layers.     

Semi-ideal solution theory. 2. Extension to conductivity of mixed electrolyte solutions

Conductivities were measured for the ternary systems NaCl-LaCl(3)-H(2)O and KCl-CdCl(2)-H(2)O and their binary subsystems NaCl-H(2)O, KCl-H(2)O, CdCl(2)-H(2)O, and LaCl(3)-H(2)O at 298.15 K. The semi-ideal solution theory for thermodynamic properties of aqueous solutions of electrolyte mixtures was used together with the Eyring absolute rate theory to study conductivity of mixed electrolyte solutions. A novel simple equation for prediction of the conductivity of mixed electrolyte solutions in terms of the data of their binary solutions was established. The measured conductivities and those reported in literature were used to test the newly established equation and the generalized Young's rule for conductivity of mixed electrolyte solutions. The comparison results show that the deviation of a ternary solution from the new conductivity equation is closely related to its isopiestic behavior and that the deviations are often within experimental uncertainty if the examined system obeys the linear isopiestic relation. While larger deviations are found in the system with large ion pairing effect, the predictions can be considerably improved by using the parameters calculated from its isopiestic results. These results imply that the previous formulation of the thermodynamic properties of aqueous solutions of electrolyte mixtures has a counterpart for transport properties.     

The effect of electrolyte conductivity on electrophoretic deposition

In this work, the influence of electrolyte conductivity on the electrophoretic deposition of alumina particles from ethanol suspensions was studied. Deposition experiments in a Hull cell showed that high-conductivity ethanol-based suspensions yield uniform deposits, while low-conductivity suspensions result in nonuniform deposits. The difference in the deposition, behavior is due to the resistance increase over the deposit during polarization. Impedance measurements during electrophoretic deposition showed that during EPD the relative deposit resistance increases much faster for the high- than for the low-conductivity suspension. The impedance measurements also showed that the resistance increase dropped almost to the suspension resistance after the electric field was turned off. This means that the resistance over the deposit is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. Negatively charged ions are depleted in the deposit by migration toward the positively charged counterelectrode, while positively charged ions undergo electrochemical reactions at the deposition electrode. This change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi-irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.     

Thermochemistry of electrolyte solutions

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N,N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water–organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N,N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules.     

A theoretical study on the photoisomerization of thiophene

The photoisomerization of thiophene (3–5 and 2–4 transpositions of carbon atoms) has been studied with ab initio SCF and CI calculations. A possible reaction mechanism from the lowest excited singlet state ¹B₂ of thiophene can be proposed from potential surface via Dewar thiophene. The ¹B₂ state of thiophene would easily convert to the biradical intermediate by almost one step. The internal conversion of this species to the S₀ state would cause to the transposition of carbon atoms. The effect of phenyl substituent is also discussed.     

Kinetic study of barrierless coagulation of sols in electrolyte solutions

The flow ultramicroscopy method is employed to investigate the coagulation kinetics of hydrosols of α-Fe₂O₃, α-Fe00H, γ-Al₂O₃, and Cr₂O₃ with electrolytes (NaCl and KCl) under conditions corresponding to the absence of an ion-electrostatic barrier. It is found that, at pH values corresponding to pH_IEP of particles, as well as at those differing from pH_IEP, but at sufficiently high ionic strengths of coagulating electrolytes, the observed rate of coagulation is close to or above that calculated in terms of the Smoluchowski theory of fast coagulation. The data obtained are analyzed and possible reasons for the observed effect are considered with regard to the fractal structure of aggregates, the polydispersity of initial particles, and the concepts of additional interparticle attractive forces arising at high electrolyte concentrations.     

A theoretical study on the protonation of benzamide

We have performed an ab initio study of the protonation of benzamide, using a STO-3G minimal basis set. According to our results, benzamide is an oxygen-base in the gas-phase. Rotation of the -CONH₂ group respect to the aromatic ring does not affect the basicity of the molecule. If the presence of the solvent causes pyrimidization of the -NH₂ group, the intrinsic basicity of the O atom decreases, while that of the N atom increases and the interaction of this center with the solvent is stronger, favoring nitrogen protonation in solution.     

Pseudolattice theory of charge transport in ionic solutions: Corresponding states law for the electric conductivity

A statistical mechanical framework for charge transport in ionic liquid–solvent mixtures based on the existence of a statistical lattice structure (pseudolattice) throughout the whole range of concentration is reported. The ion distribution is treated in a mean-field Bragg–Williams-like fashion, and the ionic motion is assumed to take place through hops between cells of two different types separated by non-random-energy barriers of different heights depending on the cell type. Assuming non-correlated ion transport, the electrical conductivity is shown to have a maximum, arising from the competition between the concentration of charge carriers in the bulk medium and their mobilities in the pseudolattice. An explicit expression for the concentration at which this maximum occurs is given in terms of microscopic parameters, and the electrical conductivity normalized by its maximum value (κ/κ_max) is shown to follow rather closely a universal corresponding states law in concentration space when represented against the ionic concentration scaled by its value at the conductivity maximum (?_α/?_max). Ion–ion and ion–solvent interactions are explicitly considered combining the path probability method for charge transport in solid electrolytes and the Bragg–Williams approximation for interparticle interactions, and their impact on the deviations of experimental data from the universal behavior of non-correlated transport analyzed. The theoretical predictions are shown to satisfactorily predict experimental values of electrical conductivity of aqueous solutions of conventional electrolytes and of mixtures of room temperature molten salts with typical solvents.     

Remarks on the theory of diffusion in electrolyte solutions

The assumptions usually made that the ionic atmosphere has spherical symmetry in the diffusion of binary electrolytes and that the electrophoretic effect is negligible in the tracer diffusion of ions are pointed out to be incorrect when terms up to order κ² ln κ (κ is the Debye-Hückel parameter) are considered.     

A study on the thermal conductivity of resilient materials

The floor system of apartments must have a certain level of floor impact sound performance (light-weight impact sound is 58 dB or less, heavy-weight impact sound is 50 dB or less), and comply with the building energy code to prevent energy loss in residential buildings in Korea. In this study, expanded polystyrene (EPS), expanded polypropylene (EPP), ethylene-vinyl acetate copolymer (EVA), polyethylene (PE) and urethane foam, which are widely used in Korea as resilient materials for floating floor system of apartments, were measured. Their thermal conductivity and apparent density were measured to analyze their thermal properties and their relation was analyzed by material. In case of resilient materials made of EPS and EPP, thermal conductivity tended to decrease as apparent density increased, whereas in case of resilient materials made of EVA and PE, as apparent density increased, thermal conductivity tended to increase as well.     

A theoretical study on the decomposition mechanism of artemisinin

A theoretical study on the artemisinin decomposition mechanism is reported. The suggested pathways have been reproduced and the appearance of the final products can be explained in a satisfactory way. In addition, several intermediates and radicals have been found as relatively stable species, thus giving support to the current hypothesis that some of these species can be responsible for the antimalarial action of artemisinin and its derivatives.