Dynamic light scattering as well as rheological technique was used to study the semi‐dilute hydrophobically modified alkali‐soluble emulsion (HASE) solutions. The solution viscosity increases dramatically, when the overlap concentration C* is exceeded. Two diffusional modes are evident from the decay time distributions of light scattering and they are related to the hydrodynamic correlation length and the apparent hydrodynamic radius of the HASE clusters. The hydrodynamic correlation lengths, as determined from the fast diffusion mode decrease in proportion to the polymer concentrations but increase with increasing the hydrophobicity of the hydrophobes of the macromonomers. The apparent hydrodynamic radii of the clusters, as determined from the slow diffusion mode, increase with increasing polymer concentrations. When the carbon number of the hydrophobes is increased from C1 to C8, both the viscosities and diffusion coefficients of the slow mode remain almost unchanged. However, they are strongly dependent on the carbon chain length when the carbon number exceeds C12, especially for the polymer with C20 alkyl chains. The solution viscosities decrease and diffusion coefficients of the slow mode increase with increasing temperatures, however, the parameters of Dη/T remain constant.
Comparison of microstructures of semi‐dilute HASE solutions with (a) short hydrophobic alkyl groups and (b) long hydrophobic alkyl groups was made. For (a) with small hydrophobes, the aggregation number per association junction is smaller and there are more aggregation junctions in the network cluster. The hydrodynamic correlation length, ξh, which is the averaged distance between two aggregation junctions, is shorter. As for (b) with larger hydrophobes, the aggregation number is larger with fewer aggregation junctions in the network cluster. The hydrodynamic correlation length is longer.
