Surface Tension Of Micellar Solutions Research Articles

Influence of solubilised dodecane on the dynamic surface tension and dilational rheology of micellar Triton X-45 and SDS solutions

Maximum bubble pressure tensiometry is used to measure the dynamic surface tensions of micellar solutions of TX45 and mixtures of SDS/TX45 at the solution/air interface. For measurements of the dilational visco-elasticity of the micellar solutions the buoyant bubble profile tensiometry with harmonic bubble surface area oscillations is applied. The influence of dodecane solubilised in TX45 and mixed SDS/TX45 micelles, respectively, on the dynamic surface tension and dilational characteristics of these micellar solutions is determined. It is shown that the solubilisation of dodecane by micelles leads to a slowdown in the dynamic surface tension change and an increase in the visco-elasticity of the micellar solutions. Theoretical models proposed earlier are used for the description of the influence of solubilised dodecane on the dynamic surface tension and visco-elasticity of micellar TX45 solutions. It is shown that the presence of solubilised dodecane leads to a decrease of the CMC value, and to a decrease of the micelles diffusion coefficient.

Dynamic surface tension of micellar solutions in the millisecond and submillisecond time range

The analysis of the available bubble life times and dead times for the bubble pressure tensiometer BPA-1S shows that dynamic surface tensions can be measured also for surfactant solutions at concentrations many times higher than the corresponding CMC. For the three nonionic surfactants Triton X-100, Triton X-45, and C 14EO 8 experiments are performed for solutions with a concentration of up to 200 times the CMC (C 14EO 8). Comparison of the experimental data with micelle kinetics models yields rate constants for the fast micelle dissolution process, which are in a good agreement with values obtained by other experimental methodologies.

Kinetics of nonionic surfactant adsorption at a fluid-fluid interface from a micellar solution

The kinetics of nonionic surfactant adsorption at a fluid-fluid interface from a micellar solution is considered theoretically. Our model takes into account the effect of micelle relaxation on the diffusion of the free surfactant molecules. It is shown that nonionic surfactants undergo either a diffusion or a kinetically limited adsorption according to the characteristic relaxation time of the micelles. This gives a new interpretation for the observed dynamical surface tension of micellar solutions.

Adsorption from Micellar Surfactant Solutions: Nonlinear Theory and Experiment

A theoretical approach to the kinetics of adsorption on the expanding interface of a micellar surfactant solution is proposed. The nonlinear partial differential equations of mass transfer of the micelles and monomers are reduced to ordinary differential equations, which are solved numerically along with the nonlinearized adsorption isotherm as a boundary condition. Being more general, this theoretical approach is consistent also with the special case of small deviations from equilibrium widely used in the kinetics of micellization. The theory is applied further to fit the experimental data for dynamic surface tension of micellar solutions of sodium dodecyl sulfate and sodium polyoxyethylene-2 sulfate measured by the maximum bubble pressure (MBP) method. The expansion of the bubble surface is accounted for by using the experimental dependence of the bubble size on time. The calculated effective rate constant of micelle decay for sodium dodecyl sulfate turns out to be sensitive to the mechanism of the micelle's disintegration. This provides a possibility for one to determine the rate constants of the fast and slow processes in the relaxation kinetics of micellization by using a relatively simple experimental technique for dynamic surface tension measurement like the MBP method.

Kinetics of the surface tension of micellar solutions: Comparison of different experimental techniques

The kinetics of the surface tension of micellar solutions of nonionic surfactant Triton X-100 is measured experimentally by means of three different techniques: oscillating jet, maximum bubble pressure and inclined plate. They allow to study the micellization kinetics at various time scales (from a few milliseconds to a few seconds) in fairly large concentration region up to 50 times CMC. The experimental data are satisfactorily explained by a theoretical model accounting for the kinetics of micellization, diffusion of surfactant species and expansion of the bubble interface. By this model are computed the characteristic times of diffusion and micellization, which are of comparable magnitude (about 5 to 200 ms), and the Gibbs' elasticity. The micellization time constant corresponds to the slow relaxation process known to coincide with the disintegration of micelles. Comparing our data with other data from literature one can conclude that more realistic information for the micellization kinetics is obtained by the maximum bubble pressure and the oscillating jet method. The inclined plate seems too slow to measure the relaxation processes in micellar solutions of this surfactant.

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method

A theoretical model for the dynamic surface tension of an air bubble expanding in micellar surfactant solution is proposed. The model accounts for the effect of expansion of the bubble surface during the adsorption of surfactant molecules (monomers) and the effect of disintegration of polydisperse micelles on the surfactant diffusion. Assuming small deviations from equilibrium and constant rate of expansion analytical expression for the surface tension and the subsurface concentration of monomers as a function of time is derived. The characteristic time of micellization is computed from the experimental data for two surfactants (sodium dodecyl sulfate and nonylphenol polyglycol ether) obtained by the maximum bubble pressure method

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method

A theoretical model for the dynamic surface tension of an air bubble expanding in surfactant solution is proposed. The model accounts for the effect of convection on the surfactant diffusion and the effect of expansion of the bubble surface during the adsorption of surfactant molecules. Assuming small deviation from equilibrium and constant rate of expansion, an analytical solution for the surface tension and the subsurface concentration as a function of time is derived. The parameters of the model are computed from experimental data for sodium dodecyl sulfate obtained by the maximum bubble pressure method.

Micelle dissociation kinetics study by dynamic surface tension of micellar solutions

The dynamic surface of sodium tetradecylsulphate and sodium bexadecylsulphate solutions in water and also in Triton X-100 solutions was measured by the maximum bubble-pressure method, using modern computerized instrumentation, for a wide range of surface lifetimes (from 0.001 to 10 s), temperatures (from 30 to 80°C) and surfactant concentrations (from 1 to 200 CMC). On the basis of a previously suggested adsorption kinetics theory for micellar solutions of ionogenic surfactants (V.B. Fainerman, Colloids Surfaces, 62 (1992) 333) a method was developed for the calculation of the micellar dissociation rate constant k. For the surfactants studied, k increases with increasing concentration. Moreover, for ionic surfactants the dependence of k on concentration ( C) becomes more striking for C> (10–30) CMC. This can be explained by a micelle shape transition and by a strengthening of the intermolecular repulsion in micelles. In solutions of the ionic surfactants the constant k increasing with increasing temperature, whereas in Triton X-100 solutions a temperature dependence is absent. This phenomenon is associated with the different nature of the molecular interactions for ionogenic and non-ionogenic surfactants in micelles. The k values, obtained from results of dynamic surface tension measurements, are in satisfactory agreement with the results of a study of the relaxation of micellar solutions published previously.

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method. 1. Experiment

The effect of the micelles on the dynamic surface tension of micellar surfactant solutions is studied experimentally by means of the maximum bubble pressure method. Different frequencies of bubbling ranging approximately between 1 and 30 s−1 are applied. The time dependence of the surface tension is calculated using a dead time correction. Water solutions of two types of surfactants with different concentrations are investigated: sodium dodecyl sulfate and nonylphenol polyglycol ether. The surface tension relaxes more quickly in the presence of micelles. The characteristic times of relaxation of the surface tension seem to be in the millisecond range. The time constants observed experimentally are explained in terms of the theory of surfactant diffusion affected by micellization kinetics.