Rheological studies of stability of colloidal silica particles dispersed in monoethylene glycol (MEG) stabilized by dodecyl hexa ethylene glycol monoether (C12E6).
The steady shear viscosity, dynamic viscoelasticity, and high shear wave rigidity modulus were measured for silica dispersions stabilized by a nonionic surfactant, dodecyl hexa ethylene glycol monoether (C(12)E(6)). Electrokinetic measurements were also obtained to help understand the role of charge on the stability of the silica particles in nonaqueous media. The dispersions were found to be stable at low levels of C(12)E(6) concentrations due to electrostatic repulsions as deduced from zeta potential data. Zeta potentials of silica particles in mono ethylene glycol (MEG) were of the order of (-)20-(-)70 mV, signifying the importance of electrostatic stabilization normally reported in aqueous media. Instability on further addition of C(12)E(6) to silica particles in MEG, a phenomenon normally obtained with high molecular weight polymers, is explained in terms of micellar bridging and hydrophobic interactions. The extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is used to model the effect of C(12)E(6) on particle stability. Viscoelasticity of silica in MEG in the presence of C(12)E(6) is also reported. Viscoelasticity was found to be due to weak flocculation resulting in a free energy increase and a decrease in configurational entropy as the dispersion was weakly strained. Viscoelastic measurements are modeled using a mode-coupling model.
Thwala
Justice M
JM
University of Swaziland, Private Bag 4, Kwaluseni M201, Swaziland, Southern Africa. jmthwala@uniswacc.uniswa.sz
Goodwin
Jim W
JW
Mills
Paul D
PD
D003102:Colloids / Q000737:chemistry*; D004986:Ether / Q000737:chemistry*; D019855:Ethylene Glycol / Q000737:chemistry*; D008954:Models, Biological; D008956:Models, Chemical; D012212:Rheology / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry*
D003102:Colloids; D004986:Ether; D012822:Silicon Dioxide; D019855:Ethylene Glycol