A microrheological study of physical gelation of hydrophobically modified associating polymers: Effects of temperature

Abstract

The rheological properties of aqueous solutions of a hydrophobically modified poly(acrylic acid) were studied by diffusing-wave spectroscopy microrheology at various concentrations and temperatures and the formation of the transient network by hydrophobic association of the polymer chains was characterized. The Winter-Chambon power-law regime was found in a high frequency range accessible by microrheology, the physical gel point was successfully determined from the uniqueness of loss tangent, confirmed by the time – cure superposition of the mean-square displacement of the probe particles whose shift factors showed the critical power-law behaviors as a function of the relative distance from the gel point. The zero-shear viscosity as a function of the polymer concentration showed a plateau near the microrheologically determined gel point, indicating the presence of clusters which break before relaxing thus are rheologically undetectable. The largest relaxed cluster size was estimated to be 40–60 nm depending of the temperature.