On the Concentration Dependence of the Mean Aggregation Number of Ionic Micelles as Determined by Stopped‐Flow Experiments

Abstract

The analysis of the amplitudes in T‐jump experiments on aqueous micellar solutions yields the dependence of the critical micelle concentration and the mean aggregation number m of the micelles on temperature, whereas p‐jump experiments yield the corresponding dependence on pressure. In this paper we have, accordingly, evaluated the dependence of m on the total detergent concentration from stopped‐flow amplitudes (i.e. from concentration‐jump experiments). The experiments were performed on H2O‐NaDS and H2O‐NaDS. It turned out that the mean aggregation number of these detergents appears to increase with increasing detergent concentration, in accord with the results of other authors who have found an increase of m with increasing concentration of an added electrolyte.

Aqueous Hexadecyltrimethylammonium Acetate Solutions: pH and Critical Micelle Concentration Evidence for Dependence of the Degree of Micelle Ionic Dissociation on Acetate Ion Concentration

“…Such differences may be indicative of a problem associated with neglecting the second right-hand term when eq 3 is integrated. Many authors reported that the aggregation number is not independent of the concentration in surfactant (or salt) and increases sharply around the cmc. ,− Since the acetate ions are very hydrophilic, a value of n as low as 30−40 at cmc is expected for the salt-free C 16 TAOAc solutions. It may therefore not be valid to neglect the d[ln( c − c w )]/ n term when deriving β from the cmc data.…”

Nonisothermal Modeling and Sensitivity Studies for Batch and Semibatch Emulsion Polymerization of Styrene

“…Understanding the mechanisms involved in free-radical polymerization requires the integration of principles from a broad array of topics from physical chemistry. References that we found helpful include those for thermodynamic partitioning of monomer, − surfactant adsorption on particle surfaces, − micellular nucleation, − reaction kinetics, and coagulation. , The books on colloid and surface science by Israelachvili and Hiemenz and Rajagopalan provide useful review and reference for particle coagulation and micellular nucleation.…”

Micellar Kinetics of a Fluorosurfactant through Stopped-Flow NMR

“…NMR quantifies either the average molecular environment (by the chemical shift) or the weighted-average reorientational correlation time (by T 2 ): both of these seem to respond quickly to a concentration jump. We cannot exclude, however, that a concentration jump in the NaPFO system leads to a slow relaxation process whose amplitude 4,5 is very small, below what could be established from the 19 F chemical shifts above. Note that SAXS is sensitive to the concentration of micelles, and therefore, it is the limits obtained for c mic that are decisive in this issue.…”

“…As far as the widely used Aniansson model of micellar kinetics [7][8][9] is concerned, the solution is divided into micelles and un-aggregated surfactant monomers. In equilibrium, c mon is close (but, for an ionic surfactant, below) 5 to cmc and the rest of the surfactants are in micelles. Directly after, say, a 1:1 dissolution with water, c mon and c mic drop to half of their original value, although the relative proportion c mon /(c mon + c mic ) is unchanged.…”

“…Upon any deviation from equilibrium, relaxation processes reestablish a new equilibrium molecular distribution among states and aggregates. This has been investigated by various methods for creating nonequilibrium situations, such as temperature-jump, pressure jump, and stopped-flow mixing, and by various detection methods, such as conductivity, turbidity, and X-ray scattering measurements. ,− Hence, two relaxation regimes were revealed with characteristic times differing by as much as 3 orders of magnitude . In the well-known theory of Aniansson et al, − the fast relaxation, often characterizable by a single time constant τ 1 , is assigned to establishing a pseudoequilibrium through monomer exchange processes, whereas the slow relaxation (τ 2 ) is indicative of stepwise disintegration and formation of micelles.…”