Phase behavior and shear thickening of HM-HEC solutions with addition of nonionic surfactant C₁₂E₅

Abstract

An experimental study was carried out to investigate phase and flow behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) solution with or without nonionic surfactant C₁₂E₅. Shear thickening behavior is observed at moderate shear rates for pure HMHEC solutions at modest concentrations. Shear thickening becomes less significant with increasing temperature and disappears at temperature reaching 25 °C for 0.2%(mass fraction) HMHEC. Also, the shear rate at which the maximum viscosity occurs increases with temperature. Addition of a very small amount of C₁₂E₅, even below its critical micellar concentration, can promote the thickening and the strongest thickening occurs at around 6×10⁻⁵(mass fraction) C₁₂E₅. A further addition, however, can suppress the thickening phenomenon that eventually disappears at high enough C₁₂E₅ concentrations. It therefore implies that when the surfactant reaches a certain amount and starts to weaken the gel strength, the imposed flow can no longer enhance the networking. While the pure HMHEC solutions always remain a single phase, phase separation takes place for polymer-surfactant mixtures when the C₁₂E₅ concentration exceeds about 1.5×10⁻⁴.

Keywords

phase behavior / shear thickening / hydrophobically modified polymer / nonionic surfactant