Influence of particle wettability on the type and stability of surfactant-free emulsions
Influence of particle wettability on the type and stability of surfactant-free emulsions
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DOI：
10.1021/la000189s
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发表时间：
2000-11-14
期刊：
影响因子：
3.9
通讯作者：
Lumsdon, SO
中科院分区：
文献类型：
--
作者：
Binks, BP;Lumsdon, SO
系统地研究了球形纳米二氧化硅粒子的润湿性对水-甲苯乳液类型和稳定性的影响。颗粒的范围从亲水性到疏水性取决于其表面上化学吸附硅烷的程度。我们表明，预测的基础上考虑的能量附着的单个粒子的油-水界面直接关系到乳液的稳定性。粉末浸渍，货架稳定性，光衍射和显微镜测量的组合用于表征系统。由非常亲水或非常疏水的颗粒稳定的乳液是大的（>100 μ m）并且对聚结不稳定。具有中等疏水性的颗粒的那些是亚微米级的，并且对聚结无限期地稳定。对于这些，在增加水的体积分数phi（w）时发生乳液的灾难性反转，并且它们对沉降或乳状液分层的稳定性增加接近反转。乳液的稳定性重力诱导的分离通过一个尖锐的最大值后，增加颗粒的疏水性，旁边的平均液滴直径的最小值。这是通用的，并且与phi（w）和形成的乳液类型无关。在一个系统中，原本非常稳定的油包水乳液在超离心场中不稳定，导致增强的沉降和最终聚结。
A systematic investigation into the influence of the wettability of spherical, nanometer-sized silica particles on the type and stability of water-toluene emulsions is described. The particles range from hydrophilic to hydrophobic depending on the extent of chemisorbed silane on their surfaces. We show that predictions based on considerations of the energy of attachment of a single particle to the oil-water interface relate directly to the stability of emulsions. A combination of powder immersion, shelf stability, light diffraction, and microscopy measurements is used to characterize the systems. Emulsions stabilized by either very hydrophilic or very hydrophobic particles are large (>100 mum) and unstable to coalescence. Those with particles of intermediate hydrophobicity are submicrometer and stable to coalescence indefinitely For these, catastrophic inversion of emulsions occurs upon increasing the volume fraction of water, phi (w), and their stability to sedimentation or creaming increases approaching inversion. The stability of emulsions to gravity-induced separation passes through a sharp maximum upon increasing the particle hydrophobicity, alongside a minimum in the average drop diameter. This is universal and independent of phi (w) and the type of emulsion formed. In one system, an otherwise very stable water-in-oil emulsion is destabilized in an ultracentrifugal field leading to enhanced sedimentation and eventual coalescence.