Dynamic light scattering of semi-dilute hydrophobically modified alkali-soluble emulsion solutions with varying length of hydrophobic alkyl chains

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 C-1 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 C-12, especially for the polymer with C-20 alkyl chains. The solution viscosities decrease and diffusion coefficients of the slow mode increase with increasing temperatures, however, the parameters of Deta/T remain constant.