Study On The Dispersion Of Magnesium Oxide Particles In Aqueous Solution.

In this paper the dispersing ability of various surfactants to superfine magnesium oxide powder in water was studied. The results show that anionic surfactants such as sodium dodecyl sulfate (SDS), dioctyl sodium sulphosuccinate (Aerosol OT, AOT), as well as sodium lignosulfonate display good dispersing ability at concentration near their cmc. The mechanism is that anionic surfactant molecules adsorb initially at particle/water interface with head-on configuration followed by forming bilayer or hemi-micelle at the interface, which endows a larger negative zeta potential (more than -30mV) and a hydrophilic surface to the particles. However at high surfactant concentration the zeta potential of the particles decreases sharply due to the increase of the counterions and constant (saturated) adsorption of the surfactant molecules, the stability of the dispersion reduces obviously as well.Cationic surfactant like cetyl trimethyl ammonium bromide (CTAB) adsorb at particle/water interface similarly, but the saturated adsorption (ca. 10-20% of that of anionic surfactant) is much lower than that of anionic surfactant due to slightly positively charged of the particle surface. The positive zeta potential of the particles due to adsorption of CTAB is not high enough to stabilize the particles dispersed in water. Similarly cationic polymer like PEI has no stabilization to the particles. Nonionic surfactant such as Triton X-100, nonionic polymer like PEG, and Zwitterionic surfactants such as alkyl betaines are all not good stabilizers to the particles dispersed in water, the main reason is that they can not endow the particle a high zeta potential.Polymer thickeners can improve the stabilization of the particle dispersion. Thus the mixtures of anionic surfactant such as SDS and AOT and the polymer thickeners such as PAM and CMC are excellent stabilizers, which can stabilize concentrated particles dispersion where the concentration of the particles can be as high as 10wt.%.