Thermodynamic Properties of Surfactant/Polymer/Water Systems with Respect to Clustering Adsorption and Intermolecular Interaction as a Function of Temperature and Polymer Concentration

Abstract

This investigation forms part of a more extensive physicochemical study of the interaction of amphiphiles with different polymers, partially as a background for a better understanding of the function of pharmaceutical excipients. For the ethyl hydroxyethyl cellulose (EHEC)/sodium dodecyl sulfate (SDS)/water system, the dialysis equilibrium between a solution containing polymer and a solution not containing polymer has been investigated over a composition interval of the amphiphile ranging from zero up to well above cmc and for the polymer from zero up to slightly above the concentration of critical overlap. It is found that the amphiphile begins to redistribute preferentially to the polymer at a “foot point” (critical aggregation concentration) concentration of 2 mM SDS, rises to a maximum value at an SDS concentration most likely corresponding to the onset of formation of normal micelles in bulk, and then decreases. The maximum adsorption corresponds to approximately two DS- ions per structural unit of the polymer. It is proposed that the results observed could be interpreted in terms of a redistribution of surfactant to the polymer coil regions leading to locally enhanced surfactant concentration, cluster formation, and adsorption. In combination with polymer reconformation this model suggests an explanation of some specific effects observed on this system: the increase in average cluster size with increasing polymer concentration, the marked decrease in intrinsic viscosity at the onset of surfactant adsorption combined with a strong hydrodynamic interaction (high value of the Huggins' constant), and the considerable increase in macroscopic viscosity during the first phase of adsorption. The decrease in specific adsorption after the maximum probably derives from changes in DS- ion activity and saturation of the polymer, as well as the formation of normal micelles. Temperature is found to have only a small influence on the redistribution in an interval from room temperature up to the cloud point. The correction for the Donnan effect is discussed and results from conductometric measurements are used to calculate the degree of dissociation of surfactant in the micellar clusters.

Amphiphilic association of ibuprofen and two nonionic cellulose derivatives in aqueous solution

“…Similar CP curves have been reported for these cellulose ethers in the presence of sodium dodecyl sulfate, SDS. 20,33 From these CP data a rough estimate of cmc of ibuprofen in the presence of the polymer fractions can be made; its value is found to be about 150-200 mM for both EHEC and HPMC. The minimum in CP observed for the EHEC/ibuprofen system is most likely a salting-out effect due to a combination of a quite hydrophobic polymer and the considerable ionic strength from >100 mM of the sodium salt of ibuprofen, resulting in conformational changes of the polymer.…”

“…This methodology has been utilized in several recent investigations of interactions in aqueous mixtures of the surfactant sodium dodecyl sulfate and nonionic cellulose ethers. 6,7,[18][19][20][21][22] Steady-State Fluorescence MeasurementssAll steady-state fluorescence measurements were performed at room temperature on a SPEX Fluorolog 2 model FL1T2 spectrometer operated in the "s" mode with 1.88 nm excitation and 0.85 nm emission bandwiths. All fluorescence measurements including time-resolved were run in duplicates, and the error was (5% or less.…”

Studies of the Interaction of Cationic Gemini Surfactants with Polymers and Triblock Copolymers in Aqueous Solution

“…The results of the dialysis experiments were corrected for the Donnan effect according to the following procedure (31,32). If one considers a mass balance for the two solutions in the dialysis equilibrium (the subscript A refers to the retentate side of the equilibrium, B to the dialysate side), then the electroneutrality condition requires that…”

Physicochemical Investigation of the Association of the Biosurfactants Sodium Cholate and Sodium Dodecanoate With Poly(ethyleneoxide)

“…Surfactant mixtures are widely employed and investigated because of their high performance in comparison with the use of only one surfactant, [1] mainly due to the synergistic effects of the physicochemical properties. One special class of surfactant is bile salts, and these biosurfactants are responsible, in vivo, for fat=lipid solubilization and transport.…”