Ionic Surfactant Concentration Research Articles

Micellar Electrokinetic Capillary Chromatography of Proteins

Separations of model proteins obtained under denaturing conditions in the presence of micellar concentrations of ionic surfactants displayed high resolution and efficiency using either bare silica or C18-derivatized silica capillaries. Superior migration time reproducibility was achieved through the use of the C18-derivatized capillaries (run-to-run migration time % RSD = 0.2), relative to that obtained in bare silica capillaries (run-to-run migration time % RSD = 2.2), in the absence of buffer replenishment. The effects of surfactant concentration and pH upon the separation of a mixture of five model proteins of varying ionic and hydrophobic character were investigated, and the application of this technique to the analysis of a recombinant DNA-derived protein in fermentation broth was demonstrated.

Equilibrium measurements of oscillatory disjoining pressures in aqueous foam films

Disjoining pressure isotherms are measured for single, isolated foam films stabilized with sodium dodecyl sulfate above the critical micelle concentration (cmc). The measured isotherms exhibit an equilibrium oscillatory component that extends out to film thicknesses as large as 50 nm. The oscillations originate from surfactant structuring within the film and are responsible for the multiple black films extensively studied by Perrin in 1918. We find that as film thickness decreases, the slopes and peak heights of the oscillations increase for each subsequent black film encountered. The discrete changes in film thickness observed at each black film transition range from 6 to 10 nm and are a function of the ionic strength and surfactant concentration. Pressures required to rupture the multiple black films are several orders of magnitude lower than the final film-rupture pressure. Finally, the oscillatory form of the disjoining pressure permits quantitative interpretation of stepwise thinning behavior observed in films containing surfactant above the cmc. 50 refs., 13 figs.

Clouding of a nonionic surfactant: The effect of added surfactants on the cloud point

The nonionic surfactant Triton X-100 is soluble in water giving only one isotropic solution phase at about 32°C. The cloud point (CP) of the aqueous system has been measured over the entire concentration range and the lower consolute temperature at about 0.2 wt% of Triton X-100 solution is obtained. The CP, at different concentrations of Triton X-100 solutions, is also determined in the presence of zwitterionic, catanionic, and ionic surfactants. At a low concentration (1 wt%) of nonionic surfactant, lecithin drastically depresses the CP, but the degree of CP depression is found to diminish with increased concentration of Triton X-100, and an increase of the CP in the presence of lecithin is observed with about 24 wt% of Triton X-100. On the other hand, the addition of decanol registers only a decrease of the CP for the concentrations of Triton X-100 employed (1–24 wt%). No significant change in the CP of the nonionic surfactant solution is observed by adding uncharged catanionic surfactants (e.g., dodecylammonium dodecanoate); the same result is obtained in the presence of simple electrolytes. The presence of small amounts of ionic surfactants (N ≈ 0.01–0.03, where N is the molar ratio of ionic surfactant to Triton X-100) in the system leads to a substantial increase in the CP of 1 wt% of the Triton X-100 solution, but the increase is relatively less with cationic (cetyltrimethylammonium with bromide or sulfate counterions) than with anionic (dodecyl sulfate with sodium or magnesium counterions) surfactants. At N = 0.01–0.02 the rise of the CP is almost linear with ionic surfactant concentration while at N ⩾ 0.02 the CP increases slowly by further addition of anionic or cationic surfactants as well as by changing the valency of the counterion. The valency of the counterion affects the CP of the nonionic surfactant system differently for different ionic surfactants. The cloud point rise in the presence of sodium dodecyl sulfate (the degree of counterion binding, β ≈ 0.55) is higher than that with magnesium dodecyl sulfate (β ≈ 0.8), whereas approximately identical rises in the CP are observed with cetyltrimethylammonium bromide (β ≈ 0.7) and cetyltrimethylammonium sulfate (β ≈ 0.8). The clouding phenomenon of the aqueous Triton X-100 system in the presence of various additives is discussed in the light of inter- and intramicellar interactions.

Flow-injection system for determination of critical micelle concentrations of ionic and nonionic surfactants

A practical technique is presented for the rapid, accurate determination of the critical micelle concentrations (CMCs) of ionic and nonionic surfactants. The precision, speed and instrumental simplicity of a flow-injection system are combined with a gradient chamber and flow-through conductance and absorbance detection to produce a system capable of determining the CMC of surfactant solutions in less than 30 min. The exponential response gradients from the resulting system are monitored by a chart recorder and simple manual calculations yield the CMC. The validity of the technique is verified by determination of the CMC values for both ionic (cetyltrimethylammonium bromide and chloride and sodium dodecyl sulfate) and nonionic (Brij-35, Brij-56, Brij-99, Triton X-100) surfactants. The proposed technique does not require the extensive solution preparation, repetitive measurements, complex instrumentation and data manipulation typical of other methods for determining CMCs.

Equilibrium and dynamics of adsorption of surfactants at fluid-fluid interfaces

Surfactant adsorption at fluid-fluid interfaces is modeled with respect to both equilibrium and dynamic behavior. A thermodynamic treatment is developed wherein the surface concentration of ionic surfactants is distinguished from their surface excess concentration by the contribution from the electrical double layer. Only the surface concentrations are assigned to the dividing surface and the electrical double layer is considered to be a part of the aqueous phase. A general adsorption isotherm is derived by including non-idealities in the bulk as well as at the dividing surface. The corresponding equation of state is derived using the Gibbs adsorption isotherm. Several well-known adsorption isotherms and equations of state arise as limiting cases of the general equations of this model. The model is shown to correlate with several published surface and interfacial tension measurements on ionic surfactant systems with or without indifferent electrolytes. Ideal behavior is observed at the interfaces of all liquid-liquid systems investigated. Surface non-idealities are observed only in gas-liquid systems. It is concluded that the non-idealities do not arise from the electrical interactions but rather from the attractive interactions between the hydrophobic tails of the adsorbed surfactant. This approach is superior to the approaches based on a Gibbsian dividing surface since it is readily applicable to the treatment of electrostatic and electrokinetic phenomena as demonstrated by a remarkable correlation achieved between the calculated values of interfacial potentials and observed electrophoretic mobilities. The model is extended using phenomenological considerations to the case of systems not at equilibrium. A continuum treatment of adsorption dynamics is formulated wherein surfactant transport in the bulk phases is described using transport equations with constant coefficients. Activation energy barriers to solute exchange between the bulk and the dividing surface are represented by kinetics of a reversible reaction. The kinetic expression corresponding to the general adsorption isotherm is derived from phenomenological considerations.

Ion Interaction: The Energetics and Mechanism of The Competitive Behavior Between Two Similarly Charged Molecules. 1. The Effect of Ionic Strength, Acetonitrile and Surfactant Concentration

Abstract The competition between two molecules of similar polarity for adsorption sites on the stationary phase is discussed in light of the effects of acetonitrile, surfactant (cyclohexylaminopropane sulfonic acid, CAPS) and salt concentrations on the retention of the thyroid hormones (3,5-diiodo-thyronine, T2; 3,3′,5-diiodo-thyronine, T3 and thyroxine, T4). The Kinetics of adsorption and desorption for the surfactant are fast which allows for actual competition, otherwise an electrostatic “wall” would be seen by the analyte leadiny to exclusion. A three-parameter equation relates the surfactant concentration and ionic strength to the retention of the hormones, which suggests that the retention and selectivity arise from the structure and “density” of the outer layer in a Stern-Gouy-Chapman model and confirms that only the outer electrical layer significantly contributes. The data are analyzed with both Langmuir and Freundlich equations which describe an intermediary state where the marginal heat of adso...

Mechanism of styrene emulsion polymerization during interval II

AbstractA systematic study of the kinetics of styrene emulsion polymerization in the postnucleation stage by the way of seed particle growth of monodisperse latices was undertaken, in which the colloidally important parameters were varied: Rp was independent (within limits) of (a) ionic strength, (b) pH, (c) initiator concentration (potassium persulfate), and (d) surfactant (sodium dodecyl sulfate) concentration; Rpp was independent (within limits) of (a) seed particle number concentration N, (b) oil:water phase ratio, and (c) monomer:polymer ratio; Rp was directly proportional to seed‐particle surface area. The viscosity average molecular weight of the polymer formed during interval II, Mv(i–j), was approximately constant and increased linearly with N. Log Mv(i–j) was inversely proportional to reaction temperature; Mv(i–j) was inversely proportional to initiator concentration. The overall activation energy of polymerization E′p was equal to the activation energy of propagation Ep during interval II. The value of kp at 60°C was 615 dm3 mol−1 s−1. Trace of oxygen seems to affect the average number of radicals per particle ī during interval II polymerization.

The effect of polar functional groups on the critical micelle concentration and hydrophobicity of ionic surfactants

The effect of polar functional groups on the critical micelle concentration and hydrophobicity of ionic surfactants

Effect of pyrazolone derivatives on the critical micelle concentration of ionic surfactants.

Effect of pyrazolone derivatives on the critical micelle concentration (cmc) of surfactants was investigated by using ionic surfactants which were sodium dodecyl sulfate (SDS) and dodecyl N-dimethylethylammonium bromide (DDAB). It is shown that antipyrine and 4-aminoantipyrine which are very water soluble is in breaking up micelles of SDS and DDAB. However, addition of phenylbutazone which is very slightly soluble in water results in increase in stability of the micelles. It is presumed from these results that the affinity of these additive for water plays an important role in stability of the micelles.

Solution/air interfaces. II. Adsorption of surfactants in dilute aqueous solutions. Anomalous oscillating jet phenomena

Anomalous dynamic tension values were obtained during the examination of dilute aqueous surfactant solutions by the oscillating jet relative method. At certain low concentrations of ionic and nonionic surfactants the surface tension increased with surface age to values above that of water before decreasing to the equilibrium value. With ionic surfactants these high surface tension values were preceded for a short time by values below that of water. It is suggested that the high dynamic tensions are associated with the presence of surfactant at low concentration in a disoriented state within the solution surface layer. An analogy is indicated between the increase of dynamic tension with age for surfactants and the increase in equilibrium surface tension with bulk concentration reported for capillary-inactive compounds in dilute solution.

Conductimetric determination of the critical micelle concentration of surfactants in salt solutions'

The conductimetric method of determining the critical micelle concentration of ionic surfactants has been used at very high ionic strengths. Data on sodium decyl and dodecyl sulfates in the presence of up to 1.0 and 0.3 N NaCl, respectively, were obtained. The problems involved in these determinations are discussed. The principal one is the unexpected equality of the equivalent conductances of micelles and monomers in the presence of about 0.35 N NaCl.

THE EFFECTS OF SURFACTANTS ON THE POTENTIAL, SHORT-CIRCUIT CURRENT, AND ION FLUXES ACROSS THE ISOLATED FROG SKIN.

AbstractIt has been shown previously that ionic surface active agents (surfactants) depolarize nerve and muscle membranes and the isolated frog skin. The isolated frog skin was used in the present studies. Measurements of skin potential, short circuit current, and of Na, K, and Cl fluxes were made to determine the relative roles of inhibition of active Na transport and increases in passive ion permeability in producing the depolarization. The electrical data were in agreement with the flux data in demonstrating that lower concentrations of ionic surfactants (0.5 mM) generally inhibit the active Na transport process but have little effect on passive ion permeability. At higher concentrations (2 mM or more) surfactants produce an increase in permeability in addition to inhibiting the“Na pump”. The outside surface of the frog skin was more sensitive to the surfactants than was the inside.