Phase Diagram For CTAB Microemulsion And Its Application

Microemulsion (ME) is composed of oil, surfactant, cosurfactant and water, which isan isotropic, optical transparent or translucent, low viscous, thermodynamically stablesystem, and is an optional medium for nanoparticle preparation. It is important to study theeffect of phase diagram and structural change on the application of ME system. In thiswork, the phase diagrams and the structral change of ME for three microemulsion systemswere studied by visual observation and conducivity method. And a preliminary study forthe preparation of hydroxyapatite nanoparticles from water-in-oil (W/O) microemulsionsystem has been done. Details are listed below.Firstly, the phase diagram for the system {Hexane (1)+[hexadecyl trimethylammonium bromide (CTAB)(21)/Butan-1-ol (22)](2)+Water (3)} at303.15K has beenconstructed by a titration and visual method. Where, CTAB is the surfactant, butan-1-ol isthe cosurfactant, hexane is the oil phase. The dependence of phase diagram on the massratio of surfactant to cosurfactant (Km=m21/m22=0.50,0.33and0.25) have been studied.There are three phase region in the phase diagram, the solid-liquid phase equilibriumregion (S/L), the microemulsion region (ME), and the oil-water two phase equilibriumregion (L1/L3). With the decrease of Km, the area of (S/L) changes little, the area of ME isreduced, and the area of (L1/L3) is increased. In the microemulsion region, the dependenceof conductivity on the water content has been considered. It shows that, the conductivitybehavior can be explained by the conductivity percolation theory. It explains thedependence of the microemulsion structure on the water content. The percolation thresholdhave been obtained from this theory.The second microemulsion system is composed of {isopropyl myristate IPM (1)+[CTAB (21)/Butan-1-ol (22)](2)+Water(3)}, where, IPM is the oil phase. The phasediagrams of this pseudo-ternary system at303.15K and at three Km=0.50,0.33and0.25conditions have been constructed by the titration and visual method. The phase diagramsimilar to the system of hexane oil phase. The effect of the water content on the conductivity in the microemulsion phase region has been studied. The structure change ofME was explained by the conductivity percolation theoryThe third system is composed of {IPM(1)+[CTAB (21)+polyoxyethylene sorbitanmonooleate (Tween-80)(22)+Butan-1-ol (23)](2)+Water(3)}, where, IPM is the oilphase, the surfactant is composed of [CTAB+(Tween-80)], and butan-1-ol is thecosurfactant. The phase diagram of this system at Km=0.5, the mass ratio of CTAB toTween-80=9/1, at303.15K have been constructed. In the microemulsion region, thedependence of the conductivity on the water content has been studied, and the transfrom ofthe microemulsion structure has been explained by the conductivity percolation theory.Additionally, the temperature effect on the phase equilibrium in the range from298.15to313.15K has been considered. The temperature effect is weak.The nanoparticles of hydroxyapatite (n-HA) was prepared from Ca(NO3)2·4H2O and(NH4)2HPO4in ME medium. The effect of the reactant concentration and the oil phase typeon the phase stability was studied by the conductivity behavior. The conductivity decreaseswith the increases in the reactant concentration. The conductivity is higher in IPM than inhexane. A salting-out effect of reactant on the ME system is observed. The n-HA wascharacterized by TEM, XRD, FTIR and TG. The shape of n-HA is different in two MEmedium (IPM and hexane as the oil phase respectively). In IPM ME, n-HA is a stick, inhexane ME, n-HA is spherical.