The average diameter of the surface pores and internal hollows were controlled on a sub-micron order by changing the preparation conditions such as diluent concentration, volume fraction of the dispersed droplets in the W/O (water in oil) emulsion, surfactant concentration monomer ratio and salt concentration in the outer aqueous phase. The effects of the preparation conditions on the capsule morphology and entrapment efficiency of water-soluble materials were investigated. In this study, cross-linked microcapsules were prepared by the in-situ polymerization of styrene and divinylbenzene and biodegradable microcapsules were prepared by the solvent evaporation method. For those who need high viscosity from an aqueous emulsion something like glycerol can be added, or a thickener such as a cellulose or some natural gum.For the preparation of microcapsules using the W/O/W (water in oil in water) emulsion system, it is essential to control various factors such as the dispersed state of the organic phase in the W/O/W emulsion, the difference in the solute concentration between the inner and outer aqueous phases and the volume fraction of the dispersed phase. Without careful choice of surfactant this might give problems about which phase is which and avoiding phase inversion is a significant challenge.Īs is common knowledge, if the bulk phase is oil then ηĠ can be relatively high. What this tells us is that to get significant viscosity increases requires φ over 0.5. You can read out viscosity values with the mouse. There is also some mixing of cause and effect - at higher φ and high λĭrop emulsification becomes more efficient and creates smaller drops.Īll you have to do is choose a range over which to plot (limited by φ max), enter η 0 and, for Taylor and for Yaron, Gal-Or and Pal, η drop. For some nanoparticles the φ can be larger than thought if they take up a significant amount of the medium to become super-sized. The data indicates that this is largely untrue and that emulsion size effects start to become significant only when φ exceeds 0.6. It is commonly believed that smaller emulsion drops give a more viscous emulsion. For simplicity, it is fixed in the app and the plot stops at φ=0.6 before the curve gets too large): Where η r is given by the following with φ m=0.637 (this is a general value which in principle can be fitted. This uses the k from the Taylor model and instead of φ uses λ=φ 0.333. Because the viscosity rises exceptionally above φ=0.64 (random close packing limit) the calculation is not performed above that value.Īn equation better suited for emulsions is also the most monstrous - the Yaron, Gal-Or. The factor of 2.5 is the default value for the "intrinsic viscosity" term. This is OK for solids but less suited for emulsions. It incorporates a "close packing" fraction φ c at which the viscosity becomes infinite. The Dougherty-Krieger formula is popular but tends to overshoot for emulsions at high φ values. For more modest k values, the Taylor equation is used: However, for emulsions this is the limiting factor when k, which is the ratio of the viscosity of the drops to that of the bulk phase, η drop/η 0 reaches a very high value. The Einstein equation obviously is the standard for solid particles. Many equations are used to describe this dependence and three are shown here. ![]() The viscosity of an emulsion depends on the initial viscosity of the bulk phase, ηĠ and the volume fraction of the drops, φ. ![]() HLD - Hydrophilic Lipophilic Difference.
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