Drop Volume Method Research Articles

Suspension stabilizers for PVC production I: Interfacial tension measurements

AbstractThe effect of commonly used suspension stabilizers on the interfacial tension of the vinyl chloride (VCM)/water interface was studied at 50°C, using the drop volume method. The measurements covered drop times from a few seconds to about 1000 s. The interfacial tension between VCM and pure water was found to be 32 mN/m. In the presence of additives, the interfacial tension varied with drop time. An equilibrium situation was probably not reached in any of these experiments. The surface activity of the poly(vinyl alcohol) increased with increasing acetate content. The interfacial tension decreased much more slowly with time in the presence of the poly(vinyl alcohol)s than with the cellulose ether tested. However, this polymer, Methocel F50, on adsorption at the interface formed a solid, mechanically strong surface film. The formation of such films was delayed by addition of ammonium laurate and/or Span 20.

Adsorption of cycloalkane and cyclopentanealkyl acids at the air/water interface

Surface tensions of aqueous solutions of cyclopropane, cyclobutane, cyclopentane, and cycloheptane carboxylic acids, and of cyclopentaneacetic and cyclopentanepropionic acids were measured at 25 °C by the drop volume method. The Traube constants for calculation of standard free energies of adsorption were estimated from second and third degree polynomial least-squares analyses, from nonlinear least-squares analysis using the Szyszkowsky equation, and graphically.The standard free energies of adsorption at the air/solution interface of cycloalkane and cycloalkanealkyl carboxylic acids are less negative than those of the corresponding straight chain acids, but not by a constant amount; the standard free energy of the CH2 group in a cycloalkane ring is −2.5 kJ mol−1 as compared to a value of −3.3 kJ mol−1 for straight chain acids.

The surface tension of water

The air—water interfacial tension has been redetermined by the capillary rise and Wilhelmy plate methods at 25°C. The drop-volume method, using the Harkins—Brown corrections, gives good values for glass tips if appropriate precautions are taken. The effect of replacing air with He or N 2 at 1 atm. was not measurable, but CO 2 at 1 atm. gives a significant lowering of the interfacial tension. Measurements over the range 20–45°C are also reported.

A comparison of the interfacial behaviour of three food proteins adsorbed at air—water and oil—water interfaces

AbstractThe adsorption behaviour of three food proteins—a soya protein isolate, a sodium caseinate and a whey protein concentrate—at a soya bean oil‐water interface has been studied by the drop volume method. The interfacial behaviour has been compared with that at an air—water interface. The kinetics of surface tension decay were evaluated in terms of different rate‐determining steps at different ionic strengths and concentrations of the proteins. The ranking order with respect to the surface activity of the proteins adsorbed at an air—water interface was the same as that at a soya bean oil—water interface. In the high concentration range the surface activity of the proteins was higher at an air‐water interface than at a soya bean oil‐water interface, whereas thereverse was found in the low concentration range. In general, the adsorption of the proteins was more diffusion controlled at an air‐water interface than at a soya bean oil‐water interface; this suggested that proteins were less folded at the soya bean oil‐water interface. A comparison of the rates of the diffusion controlled steps for the proteins at air‐water and soya bean oil‐water interfaces indicated that the solvation energy gained when caseinates adsorb at the soya bean oil interface was enhanced compared with the other two proteins. This indicated an enhanced loop formation of the caseinate molecules in the oil phase when adsorbing at this interface, as compared with the air‐water interface.

A study of the surface enlargement in the drop volume method and its relation to protein adsorption at [formula omitted] and [formula omitted] interfaces

In the drop volume method the surface of the drop enlarges throughout the process of the interfacial tension decay. This surface expansion has been measured for drops of various sizes and shapes, where the interfacial tension depression was caused by different proteins such as lysozyme, β-lactoglobulin, bovine serum albumin, sodium caseinate, whey protein concentrate and soy protein isolate at different initial bulk-phase concentrations. The results showed that the surface enlargement could be as large as 33–34% in relation to the initial surface of the drop, and that this surface expansion was mainly dependent on the surface tension decay and the shape of the drop, irrespective of type of protein and protein concentration used. It was found within the limits of error that time of detachment for a drop was not influenced by its surface expansion. These findings make it possible to use the drop volume method for measuring protein adsorption at different interfaces, which has been shown for lysozyme adsorption at the soybean oil-water interface.

Theory on the determination of the dynamic surface tension with the drop volume and maximum bubble pressure methods

Theory on the determination of the dynamic surface tension with the drop volume and maximum bubble pressure methods

The influence of molecular architecture on the surface activity of vinyl alcohol-acetate copolymers

The interfacial behavior of a family of blocky and random vinyl alcohol-acetate copolymers and their parent polyvinyl alcohol was studied. The vinyl acetate content and the intramolecular distribution were the only variables in the molecular architecture. Polymer adsorption and the effect of spread layers of these (co)polymers at the water- 1-butanol interface were studied with the static drop shape and the dynamic drop volume methods, and in addition with a novel method that records the retardation of mass transfer across an interface as caused by polymer adsorption. The three measuring techniques provide consistent views as to which molecular parameters determine the efficiency and mode of copolymer adsorption. Not the copolymer-solvent interaction parameter is relevant in this system, but rather the molecular architecture of the copolymers as expressed by the product of the mass average vinyl acetate sequence length and the vinyl acetate mole fraction. In addition, mass transfer studies provide information on the compressibility of the copolymer layers, the effectiveness of adsorption, and the onset of adsorption fractionation.

Preparation and characterisation of the C10 to C18 even‐numbered triethanolamine alkyl sulphates

Synopsis The preparation and characterisation of purified C(10) to C(18) even-numbered triethano-lamine alkyl sulphates are described. Critical micelle concentrations were determined at 25 degrees C, using both conductance and drop volume methods. The authenticity and purity of the products are established, and evidence presented for amending the accepted melting points for two of the compounds.

The application of the drop volume technique to measurements of the adsorption of proteins at interfaces

A new procedure for the application of the drop volume technique to measurements of the rate of adsorption of proteins at interfaces has been developed. The mode of adsorption of the proteins lysozyme, β-lactoglobulin and bovine serum albumin (BSA) at the air-water interface has been measured with the drop volume method and has been compared to measurements with the Wilhelmy plate technique. Due to surface enlargement of the drop throughout the process of the surface tension decay, slower kinetics of the adsorption process is obtained by the drop volume method compared to the Wilhelmy plate technique, and the proteins investigated were differently sensitive to this surface expansion. The adsorption process of the proteins has been evaluated in terms of different rate-determining processes. Different intermediate states between the native and the denatured forms have been observed.

Automated Drop Volume Apparatus for Surface Tension Measurement

The drop volume method for surface tension measurements is ideal for new compounds since only a few milligrams are needed to obtain the CMC. However, the method is tedious and time consuming. An automated drop volume apparatus was constructed which provides sufficient accuracy with very little operator time. It is based on measurement of the average time between falling drops delivered from a constant-rate motorized syringe.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. III. The Effects of Salt on the Adsorption of Sodium Dodecylsulfate

Abstract The adsorbed amounts were measured on the surface of aqueous solutions containing tritiated sodium dodecylsulfate (TSDS) and varying amounts of NaCl by the direct radiotracer method. The surface tensions were also measured for the same solutions by the drop-volume method. The Gibbs adsorption isotherm, derived without assuming the adsorption of the chloride ion, was applied, and the amounts of adsorption were calculated for both dodecylsulfate and chloride ions. The observed amounts of dodecylsulfate adsorption were confirmed to be in good agreement with those calculated, and the calculated amounts of chloride adsorption turned out to be nearly zero or slightly negative, which is usually theoretically assumed because of the ionic repulsion due to the adsorbed dodecylsulfate. Further, the adsorption of the dodecylsulfate ion attained a constant and saturate value beyond a certain concentration (SAC) below the critical micelle concentration (CMC). The logarithms of SAC were found to vary linearly with the logarithms of CMC for the range of salt concentration studied. The value of SAC being in a close relation with the surface phenomena is considered to be another measure of the surface activity of surfactants.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. II. The Effect of Excess Salt on the Adsorption of Sodium Dodecylsulfate

Abstract The adsorbed amount and the surface tension at the air-solution interface of the solution of tritiated sodium dodecylsulfate in the presence of excess common inorganic salt have been accurately measured at 25°C. The radioactivity of tritium β-rays over the solution was counted with a sheet scintillation counter and the surface tension of the solution was measured by a drop volume method. In the sodium dodecylsulfate solution containing sodium chloride of 0.115 mol/l, the adsorbed amount of dodecylsulfate ions was saturated to give 4.33×10−10 mol/cm2 when the bulk concentration was higher than 5.0×10−4 mol/1000 g solution. In the presence of the excess inorganic salt common to the ionic surfactant in solution the Gibbs adsorption isotherm has been experimentally proved to be valid for n=1. Moreover, it was confirmed that the equation of state for the ionic adsorbed film on the salt-free solution proposed previously is also applicable to the ionic surfactant solution with the excess salt.

A drop volume method for the determination of the equilibrium interfacial tension by means of the hanging mercury drop electrode

A drop volume method is described for the determination of the interfacial tension in conditions of adsorption equilibrium by means of a hanging mercury drop electrode.

A drop volume method for the determination of the equilibrium interfacial tension by means of the hanging mercury drop electrode

A drop volume method for the determination of the equilibrium interfacial tension by means of the hanging mercury drop electrode

Adsorption of short-chain fatty acids and their ions at the oil/water interface

Interfacial tension of the oil/water system has been measured by the drop-volume method as a function of the aqueous concentration of a number of short-chain monocarboxylic acids and their sodium salts. The derived pressure-area data of the unionized acids have been found to obey, in general, Langmuir's equation of state for the mobile monolayer whereby the co-area ( A 0) per adsorbed molecule has been evaluated. The data have also been found to fit satisfactorily with the adsorption isotherm for the mobile monolayer at the liquid-liquid interface. The adsorption energies of the acids and their sodium salts calculated with the help of this isotherm have been compared.

Tabulated correction factors for the drop-weight-volume determination of surface and interfacial tensions

The determination of boundary tensions by the drop-weight or drop-volume method entails using correction factors derived by Harkins and Brown from their data relating the volume of a drop falling from a capillary tip and the radius of the capillary to the volume of a hypothetical ideal drop. In practice it is often necessary to interpolate between tabulated values of the correction factors. To eliminate the errors associated with either linear or graphic interpolation, the original data were subjected to regression analysis and a “best-fit” equation was obtained. This equation was used to generate a table of correction factors at 0.001 unit intervals of r/V13, where r is capillary radius and V is drop volume. Statistical analyses of the data and the regression are also reported.

Precipitation phenomena of heavy metal soaps in aqueous solutions: I. Calcium Oleate

Aqueous sols of calcium olcate were prepared by mixing solutions of calcium nitrate with solutions of potassium oleate. It was found that above a certain excess concentration of oleate ions for a given concentration of calcium nitrate the turbidity drops sharply. The higher the concentration of Ca(NO 3) 2, the more K-oleate is required to produce sols of low turbidity. The entire “log [Ca(NO 3) 2]-log [K-oleate]” domain giving the transition boundary between the sols of high and low turbidity has been established. The transition boundary is linear over two orders of magnitude in concentration of precipitating components. Surface tensions of aqueous sols of calcium oleate were determined using the drop volume method, and considerable aging of the sols was observed. After 3–4 hours the surface tensions of the sols reach a steady value. The latter values were independent of the concentration of calcium nitrate in sols of low turbidity but sharply increased with increasing concentration of Ca(NO 3) 2 in sols of high turbidity. Electrophoresis showed calcium oleate particles to be strongly negatively charged even in moderate excess of calcium ions.

The surface activity of phenothiazine derivatives at the air-solution interface

The surface activity of triflupromazine, chlorpromazine, promazine, promethazine, and chlorpromazine sulfoxide has been determined at the air-solution interface by the drop-volume method to measure surface tension. Differences in the abilities of the various phenothiazines employed to affect surface pressure development seem correlated with their relative nonpolarities. Anionic buffer ingredients appear to have an affect on surface activity at pH 5.0. Increasing concentrations of phthalate, citrate, and succinate buffers tend to increase surface activity, while increasing the concentration of the acetate buffer has the opposite effect. Raising the pH greatly increases surface activity of chlorpromazine and its sulfoxide, but the low solubility of the un-ionized form of chlorpromazine prevents it from exhibiting surface activity unless a significant amount of protonated form is also present. The un-ionized form of chlorpromazine sulfoxide is more soluble than chlorpromazine, and it exhibits marked surface activity at high pH.

Technique for Making Dropping Tips for Measurement of Surface or Interfacial Tension by the Drop Volume Method

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Interfacial Properties of Antimicrobial Long-Chain Quaternary Ammonium Salts I: Soluble Films at the Air—Water Interface

The surface tension of solutions containing selected long-chain quaternary ammonium compounds, having the same chain-length and counterion but differing in their polar group, was measured using the drop-volume method. The Gibbs adsorption equation was applied to obtain the surface concentration for each bulk concentration used. Data obtained in very dilute solutions conform to the equation of state for an ideal two-dimensional “gaseous” monomolecular film; whereas at higher concentrations, the films are in a “liquid-condensed” state. The standard free energy, entropy, and enthalpy for adsorption were calculated from data obtained in the ideal region. It appears that the change in entropy is the major thermodynamic factor involved in the adsorption process under study. Differences in adsorption for these compounds are discussed on the basis of the electronic and steric configuration of the polar groups. The surface tension of solutions containing selected long-chain quaternary ammonium compounds, having the same chain-length and counterion but differing in their polar group, was measured using the drop-volume method. The Gibbs adsorption equation was applied to obtain the surface concentration for each bulk concentration used. Data obtained in very dilute solutions conform to the equation of state for an ideal two-dimensional “gaseous” monomolecular film; whereas at higher concentrations, the films are in a “liquid-condensed” state. The standard free energy, entropy, and enthalpy for adsorption were calculated from data obtained in the ideal region. It appears that the change in entropy is the major thermodynamic factor involved in the adsorption process under study. Differences in adsorption for these compounds are discussed on the basis of the electronic and steric configuration of the polar groups.