The specific interaction between a strongly hydrophobic but still water-soluble cellulose derivative, ethyl(hydroxyethy1)cellulose (EHEC), and a low molecular weight anionic surfactant, sodium dodecyl sulfate (SDS), is studied in dilute solution without added neutral electrolyte by means of hydrodynamic (viscosity) and thermodynamic (dialysis equilibrium) measurements. The dialysis equilibrium shows strong adsorption of SDS at concentrations far below the normal cmc for SDS. The dialysis equilibrium is sensitive to the polymer concentration at higher SDS concentrations where the adsorption seems to decrease. In the region of increasing adsorption of SDS to EHEC the hydrodynamic measurements reveal a drastic reconformation of the polymer in dilute solution leading to a 4-fold reduction in hydrodynamic volume. At higher polymer concentrations the viscosity passes through a very marked maximum when the SDS concentration is increased. The results are interpreted in terms of a clustering theory for the SDS adsorption.

The interaction between the hydrophobic, nonionic cellulose derivative ethyl hydroxyethyl cellulose (EHEC; fraction CST-103) and the anionic surfactant sodium dodecyl sulfate (SDS) has been studied as a function of temperature from 20 to 50 °C in dilute aqueous solutions, i.e. a polymer concentration slightly below the critical overlap concentration (c*) and a surfactant concentration up to three times the normal critical micelle concentration (cmc). Methods utilized in this investigation include equilibrium dialysis and steady-state fluorescence quenching. The results show that the average aggregation numbers of the polymer-bound SDS clusters decrease with an increase in temperature although the magnitude of the effect is composition dependent and is most pronounced for compositions which give the largest cluster sizes. The adsorption of SDS to EHEC shows a break-point at an intermediate value of the adsorption isotherm above which the cooperativity increases. This break-point diminishes and disappears, i.e. the cooperativity decreases, as the temperature increases up to 50 °C. It is suggested that the mechanism responsible for these two steps in the adsorption process is at first adsorption of SDS to aggregated EHEC chains and then to a mainly deaggregated state of EHEC. The critical surfactant concentration where the adsorption to the polymer starts seems to be slightly shifted toward lower values as the temperature is raised from 20 to 50 °C. To summarize the results, the interaction between EHEC and SDS gets more intensive as the temperature is raised. Two fluorophore/quencher pairs, which previously have been used for determination of average aggregation numbers in aqueous surfactant and polymer−surfactant systems utilizing the steady-state fluorescence quenching technique, are compared. A good agreement between the two pairs is reported. Reference measurements of average aggregation numbers and adsorption isotherms for the PEO/SDS/water system are also given.

No abstract

Hydrodynamic properties and interactions between ethyl(hydroxylethyl)cellulose (EHEC) and sodium dodecyl sulfate (SDS) in water solution are discussed as a function of temperature in a composition interval of the surfactant ranging from zero up to well above the critical micelle concentration (cmc) and for the polymer concentration from zero up to slightly above the concentration of critical overlap, at temperatures between 20 and 34 °C, which is the limit of phase separation. The results from viscometric measurements, equilibrium dialysis, cloud point determinations, and conductometric measurements show a strong interaction when small amounts of SDS are added to an EHEC solution. For solutions with polymer concentrations in the range between 0.15 and 0.25% and a total SDS concentration of about 2 mM, a large increase in reduced viscosity is observed. The reduced viscosity passes through a maximum, followed by a marked decrease for SDS concentrations >5 mM. Further additions of surfactant to the polymer solution result in about half the value of the reduced viscosity displayed by the pure polymer solution. The SDS−EHEC composition, which shows an increase in reduced viscosity, corresponds to the onset of surfactant redistribution. These effects persist at elevated temperatures although they are shifted to somewhat lower SDS concentrations, but a second maximum in reduced viscosity develops upon raising the temperature when the concentration of the added SDS is in the vicinity of the surfactant cmc. At all temperatures the equilibrium dialysis shows that the redistribution increases with added SDS until normal micelles begin to form in the bulk solution. The intrinsic viscosity was found to decrease with increasing amount of redistributed SDS to EHEC. The investigation is part of a study concerning thermodynamic and hydrodynamic interactions in systems containing amphiphiles and uncharged polymers1-4 of interest for applications, for instance, in drug formulations.

CAB seems to be a useful supplement to MMSE and a screening instrument for MCI and dementia with good sensitivity and specificity.