Microviscosity in Clusters of Ethyl Hydroxyethyl Cellulose and Sodium Dodecyl Sulfate Formed in Dilute Aqueous Solutions As Determined with Fluorescence Probe Techniques

Abstract

The microviscosity has been measured in dilute aqueous solutions of ethyl hydroxyethyl cellulose (EHEC) and sodium dodecyl sulfate (SDS) by utilizing three steady-state fluorescence probe techniques: intramolecular excimer formation by 1,3-di(1-pyrenyl)propane (P3P), fluorescence depolarization of perylene, and intramolecular rotational relaxation about bonds with (p-(dimethylamino)benzylidene)malononitrile (BMN). Results obtained by the three techniques are compared. They all detect qualitatively the same behavior with a well-developed maximum in microviscosity and rigidity of the EHEC/SDS clusters formed at a surfactant concentration close to or slightly higher than the critical surfactant concentration where adsorption to the polymer starts. The EHEC/SDS clusters have, independent of composition, higher microviscosities than ordinary SDS micelles. The microviscosity is also compared with other EHEC/SDS/water system features such as the bulk viscosity, the actual adsorption isotherm, the average aggregation numbers, and the micropolarity as sensed by pyrene of the EHEC/SDS clusters formed. The maximum in microviscosity corresponds to a rather low degree of SDS adsorption to EHEC (≈0.5 mmol of SDS per gram of EHEC) and a low aggregation number (≈10) where the polymer content of each polymer-bound surfactant cluster is high. It coincides (according to the surfactant concentration) with a maximum in bulk viscosity for polymer concentrations higher than the critical overlap concentration (c*). It is suggested that the maximum in bulk viscosity is due to a three-dimensional network of polymer and cluster tie points while the maximum in microviscosity is related to a high content of hydrophobic polymer segments which stabilizes the surfactant clusters.

Fluorescence Anisotropy of Probes Solubilized in Micelles of Tetradecyltrymethylammonium Bromide: Effect of Ethylene Glycol Added

“…Experimental data are used to estimate the microviscosity around the probe. Due to the difficulties inherent to the experimental technique used in this work (27)(28)(29), all the values of microviscosity presented here are interpreted and should be considered only as qualitative observations revealing the microenvironmental modifications induced by the presence of EG in the solvent mixture.…”

Effect of Polymer Molecular Weight on Nanocomminution of Poorly Soluble Drug

“…This relatively long equilibration time cannot be entirely explained by the slow adsorption of higher molecular weight chains. Compared with the previous experimental and theoretical studies on polymer adsorption (Berglund et al 2003a(Berglund et al , 2003bEvertsson and Nilsson, 1997), our drug surfaces that are continually dissolving and precipitating are "non-ideal." Furthermore, during nanocomminution, the situation is complex since the fracturing process continually generates fresh surfaces and the aggregation process continually destroys these surfaces.…”

“…Furthermore, during nanocomminution, the situation is complex since the fracturing process continually generates fresh surfaces and the aggregation process continually destroys these surfaces. Therefore, it is more difficult to achieve an equilibrium of physical adsorption through nanocomminution than through an 'ideal' adsorption experiment using nondissolving surfaces (Berglund et al 2003a(Berglund et al , 2003bEvertsson and Nilsson 1997).…”

Influence of Counterion on the Interaction of Dodecyl Sulfates and Cellulose Ethers

“…A high I M /I E indicates also a lower probability for intramolecular excimer formation and a relatively high microviscosity. P3P has been used in this laboratory to measure the microviscosity in polymer/surfactant systems (9,30,31,33) and the method has been validated by NMR relaxation measurements (34).…”