CLUSTERING OF MICELLES IN AQUEOUS-SOLUTIONS OF TETRAOXYETHYLENE-N-OCTYL ETHER (C(8)E(4)) AS MONITORED BY STATIC AND DYNAMIC LIGHT-SCATTERING

Aqueous solutions of the nonionic surfactant C(8)E(4) have been studied by combined static and dynamic light scattering in a wide composition range up to about 25 wt % of surfactant at temperatures from 15 to 40 degrees C. This composition and temperature range lies below the upper miscibility gap with a lower critical solution temperature T-c approximate to 39.5-40 degrees C and a critical concentration W-c approximate to 7 wt %. In the whole experimental range the scattering behavior is dominated by a clustering of surfactant micelles which are invariant in size and shape. With increasing temperature, a pronounced increase of the apparent molar masses M(app) and the apparent hydrodynamic radii R(h,app) is observed in the entire concentration range. An analysis of the mass-to-radius relation of the clusters at constant concentrations supports a structure model of clusters growing in a selfsimilar manner with increasing temperature. A simple model calculation shows that the particle mass of the aggregates has a maximum at about the critical composition w, and decreases with further increasing fraction of the surfactant. At low concentrations, below the critical composition W-c the structure of these aggregates resembles that of randomly branched swollen polymer clusters. At higher fractions of the surfactant the clusters become less compact to eventually yield a scattering behavior which is typical for wormlike polymer chains.