Light Scattering of Hydrophobically Modified Alkali-Soluble Emulsion (HASE) Polymer: Ionic Strength and Temperature Effects

Novel hydrophobically modified alkali-soluble emulsion (HASE) polymers consisting of methacrylic acid (MAA) and ethyl acrylate (EA) backbone with small amounts of hydrophobic macromonomers grafted to it were synthesized for the present study. The pH, ionic strength as well as temperatures significantly alter the dilute solution properties. At low pH and without the addition of a base, the polymer is water-insoluble and exists as latex. When a base is added, the methacrylic acid groups are neutralized and the polymer solubilizes. The apparent hydrodynamic size increases to a maximum, then decreases to a minimum and thereafter increases to a constant value. With increasing salt concentration, the apparent diffusion coefficients of aggregates and unimers increase and this behavior differs from that of pure polyelectrolyte solutions. Fractal dimensions from intensity light scattering reveal that the structure becomes more compact with increasing salt concentration. A pictorial description of the microstructure at low and high ionic strength is proposed, based on the results of both dynamic and static light scattering. Meanwhile, increasing temperature yields correspondingly higher apparent diffusion coefficients, which can be described by the Arrhenius relationship. However, the reduced diffusion coefficients, fractal dimensions as well as the apparent hydrodynamic sizes are independent of temperature.