| The emulsifying and stablilizing effects of layered double hydroxides——magnesium aluminum hydroxides (MAH) on liquid paraffin, benzene and rosin solutions as a microparticle emulsifier either alone or together with other adjuvants were investigated systematically.Liquid paraffin/water can be emulsified into o/w emulsion by MAH when initial oil and water volume fraction was less than 3:1. The stability of paraffin emulsion was improved by increasing paraffin volume fraction and MAH addition level, accompanied by the increase of emulsion viscosity. However, the droplet size increased with increasing paraffin volume fraction while decreased with increasing MAH addition level. Sodium citrate can induce the aggregation of MAH particles and improve the adsorption of MAH on the paraffin/water interface. The formed open aggregates with high viscosity may improve the stability of the MAH stabilized paraffin/water emulsion. However, the emulsion viscosity was also increased. When the addition level of sodium citrate was too large, denser MAH aggregates were formed and the stability of paraffin-in-water emulsion was lowered while the emulsion droplet size was rapidly increased. Sodium-activated bentonite can induce the coagulation of MAH and improve the adsorption of MAH on the paraffin/water interface. Small amount of bentonite can improve the stability of paraffin/water emulsion prominently; meanwhile, the viscosity and droplet size were also increased.Benzene/water can be emulsified into o/w emulsion by MAH, but the stability of benzene emulsion was poor even at large addition levels of MAH. However, when rosin was dissolved in benzene, the polarity of oil phase and three-phase contact angle of MAH were enhanced. As result, the hydrophilic MAH displayed a hydrophobic nature at the oil/water interface, and w/o emulsions with excellent stability were formed. The emulsion stability was improved by increasing the rosin concentration of oil phase and the initial water volume fraction, accompanied by the increase of emulsion viscosity and droplet size. Meanwhile, the stable water-in- rosin solution could be obtained by adding a small amount of MAH particles.Rosin solution, which was prepared by dissolving rosin in benzene at mass ratio of 1:1, could be emulsified into a stable w/o emulsion by MAH. The emulsion stability could be further improved with increasing the initial water volume fraction and addition level of MAH while the emulsion viscosity was increased and the droplet size was decreased. However, the too large dosage of MAH was harmful to the stability of emulsion. During the emulsifying process, the higher mechanical force led to more stable emulsion with smaller droplets. The aggregation of MAH particles caused by NaCl was adverse to the stability of emulsion. Increasing salt concentration lowered the emulsion stability, increased the emulsion viscosity and decreased the emulsion droplet size.The water-soluble polymer (WSP) and organic microparticles (OMP) favored to stabilize w/o emulsions when 50wt% rosin solution was used as oil phase. When the MAH and WSP or OMP were used together, different types of rosin emulsion could be obtained by adjusting the relative amount of MAH and WSP or OMP at the initial oil-water volume fraction of 1:2. The emulsion stability was also enhanced by the co-emulsifying effect of MAH and WSP or OMP at suitable addition levels. Generally speaking, the rosin solution-in-water emulsion was more stable. |
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