Surface Tension Of Surfactant Solutions Research Articles

Bubble volume method for the measurement of dynamic surface tension of surfactant solutions

This paper concerns a buble volume method derived from the maximum bubble pressure method for measurement of surface tension of liquids. This new, simple method is based on a steady-state expansion of a single air bubble formed on the bubble tip turned upward in liquid until detachment from the tip; through measurement of the detached bubble volume, the liquid surface tension is obtained. The empirical relationship between the volume and the expanding time obtained for several pure liquids and aqueous solutions was found to be very similar to that between the drop weight (or volume) and the dropping time obtained by the drop weight technique. The analytical treatment of the experimental data gives the dynamic surface tension of C 12E 5 (dodecyl pentaethylene glycol) solutions. Evaluation with the adsorption equation for surface dilatation showed that the dynamic surface tension obeys diffusion-controlled adsorption kinetics as expected.

A molecular theory of the surface tension of surfactant solutions

Through the experimental investigations carried out by Motomura and co-workers it has been shown that for surfactant solution/air interfaces there is generally a Henry's law region at low surfactant concentrations ( c < 0.1 c.m.c.) where the surface tension γ drops slowly with increasing concentration in a linear fashion. This behaviour is consistent with assuming a “gaseous” surface state with molecularly dispersed surfactant molecules. At about c = 0.1 c.m.c. a first-order surface phase transition occurs (corresponding with a breakpoint in the surface tension versus concentration curve) which results in the formation of a condensed monolayer of the liquid-expanded type. Upon raising the surfactant concentration further in the range above the transition (0.1 c.m.c. < c < c.m.c.) γ drops much more rapidly down to 30–35 mN m −1. In order to account for surface tension data of this kind obtained by Motomura et al. for dodecylammonium chloride (C 12NH + 3Cl −) solutions, we have modelled the surfactant monolayer region by assuming the following excess free energy contributions: (i) the free energy change associated with transferring a hydrocarbon chain from water to liquid hydrocarbon as quantified by Tanford; (ii) the electrostatic free energy computed according to the Gouy—Chapman theory; (iii) the configurational free energy of the hydrocarbon chains as obtained from the statistical mechanical calculations of Gruen; (iv) a hydrocarbon/water contact free energy which was set equal to its macroscopic value at oil/water interfaces (∼ 50 mJ m −2). The resulting computation scheme also includes options to have dodecyl alcohol (C 12OH) and a salt present in the surfactant solution. The monolayer—solution equilibrium is established by means of numerical iteration procedures. Satisfactory agreement is demonstrated with the experimental γ data for C 12NH + 2Cl − solutions, implying that the main contributions to the lowering of the (mechanical) γ value are the electrostatic surface pressure and (below about 50 Å 2/chain) the packing-dependent surface pressure in the condensed hydrocarbon layer. Furthermore, on this basis we can propose that the first-order surface phase transition between the gaseous state and a (stretched) liquid-expanded state (which gives rise to a step-isotherm) is hydrophobically driven. In addition, calculation results concerning the effects of adding salt and C 12OH are presented and it is demonstrated that surfactant penetration of an insoluble monolayer can be readily analyzed in molecular terms by employing our theoretical approach.

A device for the automatic determination of the surface tension of surfactant solutions

An experimental device and procedure are described for the fully automatic determination of the surface tension of liquids and (particularly) surfactant solutions. The computer-controlled system is capable of yielding precise and reproducible values of that quantity. The possibilities of equilibration times selected by the user, cleaning the surface by suction, and adding fresh solution prior to each measurement are emphasised among other capabilities. As an example, a solution of sodium dodecylsulphate (10-3 mol dm-3) plus sodium chloride (10-2 mol dm-3) is extensively studied.

HIGH-FREQUENCY SINGLE DROP FORMATION: PHENOMENOLOGY AND THE EFFECT OF SURFACTANTS

The phenomenology of high-frequency single drop formation from a capillary in air has been studied for single liquids and surfactant solutions. Attention has been given mostly to the region of high flow rates, close to the transition from single drops to a continuous jet. At these flow rates, periodicity and “chaotic” behavior have been elucidated in terms of the drop volume. A linear correlation between the transition flow rate and γD/ρ has been observed, where γ and ρ are the surface tension and density of the liquid, and D is the diameter of the capillary. This correlation may be useful for monitoring surface tension variations in continuous processes, and for estimating dynamic surface tensions of surfactant solutions, for surface ages of about 10-50 msec. An appreciable effect of the surfactant concentration on the transition flow rate has been noted within a certain concentration range. The CMC values of the surfactants fall in this range, an observation which suggests a new possible approach to the...

A protein from airways of premature lambs that inhibits surfactant function.

A protein that interfered with surfactant function was isolated from the alveolar washes of prematurely delivered and ventilated lambs. This inhibitor was recovered following sequential precipitation with polyethylene glycol, Affi-Gel Blue, and diethylaminoethyl (DEAE) cellulose chromatography as a protein of approximately 110,000 mol wt. Compared to surfactant alone or surfactant and bovine serum albumin, the purified inhibitor increased the time required for surfactant to spread, increased both maximal and minimal surface tensions, increased the percent surface area that had to be compressed to reach a minimum surface tension of less than 15 dyn/cm, and delayed the surface adsorption of surfactant. The effect of inhibitor on the minimum surface tensions of surfactant solutions was inversely related to surfactant concentration. A radioimmunoassay was used to estimate that approximately 10% of the protein from plasma of premature lambs and alveolar washes after 4 h of ventilation was inhibitory. Following the simultaneous intravascular injection of labeled inhibitor and bovine serum albumin, about 4% of the radioactivity associated with both proteins was recovered in alveolar washes and 6% was associated with lung tissue after alveolar wash. This large proportionate leakage of both proteins did not occur in other tissues. The inhibitor affected multiple measurements of surfactant function in vitro and its presence may contribute to a surfactant deficiency state in the immature lung.

On the determination of dynamic surface tensions by means of a modified bubble pressure method

A method for the determination of the dynamic surface tension of surfactant solutions is presented which allows to cover adsorption times down to 10 seconds. This method is based on the determination of the pressure inside two communicating bubbles. There is no deformation of the solution/air interface during the experimental procedure. Hence, in evaluating the kinetic data no surface area enlargement has to be taken into account. An automatically operating procedure should allow to cover adsorption times down to approximately one second and should improve the measuring accuracy substantially. Experimental investigations with aqueous n-decanoic acid solutions using the method proposed provided evidence that decanoic acid is adsorbed by a diffusioncontrolled mechanism.

Determination of the surface tension of surfactant solutions applying the method of Lecomte du Noüy (ring tensiometer)

Starting from a comparative assessment of the outstanding works on the ring method (du Nouy) for the determination of the surface tension of liquids and its solutions it is shown that the application of this method to surfactant solutions can lead to substantial errors if one follows conventional conditions. These errors are mainly connected with so far unknown phenomena occurring during the raising of the ring and concerning the influence of the hydrophilic vessel wall above the solution level and the stretching of the solution surface. This is demonstrated quantitatively with surfactant solutions of different kind and concentration. These effects can be explained theoretically very simply by introducing certain assumptions on the behaviour of a surfactant adsorption layer on the inner vessel wall. Conditions leading to the elimination of these errors are given, thus enabling the application of the ring method to the determination of the surface tension of surfactant solutions.

On the applicability of the du Nouy (ring) tensiometer method for the determination of surface tensions of surfactant solutions

On the applicability of the du Nouy (ring) tensiometer method for the determination of surface tensions of surfactant solutions

Equilibrium surface tension of aqueous surfactant solutions

The applicability of the drop weight method for determining time dependent surface tension of surfactant solutions was experimentally proved.

Effect of Inorganic Additives on Solutions of Nonionic Surfactants III: CMC's and Surface Properties

Continuing work on the interaction of inorganic additives with nonionic surfactants in aqueous solution dealt with their effect on the CMC and surface tension. The surfactants were octoxynol and polyoxyethylated oleyl alcohol, containing an average of 9.5 and 10 ethylene oxide units, respectively. Their CMC values were lowered by most electrolytes studied, representing salting out of the surfactants. The steepest reductions in the CMC were produced by the nitrates of sodium and potassium, which had been found to lower the cloud points of nonionic surfactants, salting them out because of the inability of their cations to form complexes with the ether oxygen linkages of the polyoxyethylene moieties. However, even electrolytes with cations such as hydrogen, lithium, calcium, nickel, lead, and aluminum capable of forming complexes with the ether oxygens, thereby increasing the cloud points of the surfactants, lowered their CMC values. In the presence of increasing concentrations of the latter electrolytes, the CMC values frequently went through minima and approached the CMC of the surfactant in the absence of additives. Increases in the CMC over the entire range of additive concentrations investigated were produced by cadmium nitrate for octoxynol, urea for polyoxyethylated oleyl alcohol, and magnesium nitrate for both. Net increases in the plateau or micellar surface tension of polyoxyethylated oleyl alcohol, i.e., in the constant surface tension of surfactant solutions above the CMC, were brought about by the nitrates of cadmium, aluminum, and magnesium at low concentrations only and by urea at all concentrations. This increase is interpreted as salting in. The area per surfactant molecule adsorbed at the air-water interface was reduced by all added electrolytes. Urea caused no such reduction.

Studies of the drop-weight method for surfactant solutions: III. Drop stability, the effect of surfactants on the stability of a column of liquid

The problem of pendant drop stability is considered in connection with the drop-weight method of measuring the surface tension of surfactant solutions. The general drop stability problem is much too complex for any analytical solution, and the cylindrical column of liquid is considered in an effort to learn something about the effects of surface active agents on the stability and drop breakaway process. The results suggest that the drop stability is independent of the rheological properties of the surface, and that the geometry of the breakaway process depends only on V/r 3 0 as suggested in Part II of this paper.

Strain Gauge Electromicrobalance for Surface Tension Measurement

Abstract Two types of apparatus using an unbonded strain gauge of a cantilever type for the measurement of surface tension were constructed. One is a sensitive electromicrobalance equipped with an extended arm attached to the cantilever of the strain gauge. The apparatus proved suitable as a surface balance in a completely closed system. By this apparatus, the measurement of surface tension ranging from 0 to 74 dyn/cm is possible with the accuracy of ±0.10 dyn/cm. The other type was constructed by connecting the sensing lever of strain gauge to the arm of a torsion balance with a strip of phosphor bronze. This device together with a counterbalance on the opposite side of the arm also proved to be useful as a tensiometer. Accuracy of this apparatus was a little better than that of the extended arm type balance, although a larger space is required. Both apparatus are inexpensive, easy to construct and simple to operate, and are suitable for the self-recording of time dependence of surface tension or weight change in general with sufficient accuracy. Equations proposed for the time dependence of surface tension of surfactant solution were checked by using the strain gauge tensiometer of the extended arm type.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. IV. Direct Measurement of Adsorption of Tritiated Nonionic Surfactant

Abstract The radio- and surface-chemically pure nonionic surfactant, C10H21(CHT)2O(C2H4O)6H, was synthesized, and surface tension and adsorbed amount of its aqueous solution were measured directly at the air-solution interface at 30°C. Surface tension was measured by the drop-volume and Wilhelmy plate methods, while adsorbed amount was measured by the radiotracer method. The adsorption isotherm showed saturation values of 2.73×10−10 mol/cm2 above the concentration of about 1/5 of the critical micelle concentration. The observed amount of adsorption was in good agreement with the values calculated from surface tension data measured by the Wilhelmy plate method by applying the Gibbs adsorption isotherm for a single solute system. The time dependence of surface tension of surfactant solution was further discussed, and the inherent time dependence was shown for pure surfactant solution.

Dynamic surface tension determination with the maximum bubble pressure method

The surface tension of surfactant solutions can be observed conveniently as a function of time in the 1- to 100-sec range with some modifications of the normal maximum bubble pressure method. Dynamic surface tensions are compared with equilibrium values for dimethyldecylphosphine oxide, dimethyldodecylphosphine oxide, dimethyldodecylamine oxide, and n-dodecylhexaoxyethylene glycol monoether. The rate of surface tension equilibration differs for these compounds, with the C 10 phosphine oxide having the fastest rate. The experimental data are in reasonable agreement with a diffusion-controlled adsorption model both for the long-time adsorption and for the short-time initial adsorption.

Measurement of surface tensions of surfactant solutions

Measurement of surface tensions of surfactant solutions