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.