Net Contribution of Hydrophobic Association to the Thickening Power of Hydrophobically Modified Polyelectrolytes Prepared by Micellar Polymerization

Abstract

Hydrophobically modified polyelectrolytes (HMPEs) have been widely used in numerous industries as rheology modifiers because of their unique solution microstructures and fascinating viscosifying ability; however, the net contribution of hydrophobic association to the thickening power of these structured fluids remains ambiguous due to the lack of comparable HMPEs and unmodified parent polyelectrolytes (PEs). In this work, a series of model HMPEs with a different hydrophobe content and length of the hydrophobic blocks in the copolymer (NH) were prepared by the micellar polymerization of acrylic acid and stearyl methacrylate, and the obtained HMPEs were further posthydrolyzed to obtain structurally similar, same-molecular-weight normal PEs by cleaving the hydrophobic pendant group. The difference in zero-shear-rate viscosity (η0,H–η0,h) between the HMPEs and PEs can be scaled versus NH and the concentration of the hydrophobic group in solution (CH) as η0,H–η0,h ∼ NH3CH3.29 when the polymer concentration exceeds the critical entanglement concentration in deionized water and as η0,H–η0,h ∼ NH3CH3.72 in a 0.02 M NaCl solution when the polymer concentration is higher than the overlap concentration, indicating the power-law contribution of the hydrophobic clustering in the HMPEs.