Key Laboratory for Colloid and Interface Chemistry of the Education Ministry, Shandong University, Jinan, Shandong 250100, PR China.
Langmuir. 2010 Apr 20;26(8):5397-404. doi: 10.1021/la903817b.
Liquid paraffin-water emulsions were prepared by homogenizing oil phases containing sorbitan oleate (Span 80) and aqueous phases containing layered double hydroxide (LDH) particles or Laponite particles. While water-in-oil (w/o) emulsions are obtained by combining LDH with Span 80, the emulsions stabilized by Laponite-Span 80 are always o/w types regardless of the Span 80 concentration. Laser-induced fluorescent confocal micrographs indicate that particles are absorbed on the emulsion surfaces, suggesting all the emulsions are stabilized by the particles. The difference of the particle-stabilized emulsion type may be explained by comparing particle contact angles and the oil-water interfacial tensions, indicating that more Span 80 molecules are adsorbed on the LDH particles than on Laponite. Apparently, the LDH particles are rendered more hydrophobic by Span 80, resulting in the formation of w/o emulsions. The long-term stability of the emulsions was also compared. Emulsions stabilized by Span 80 alone completely separate into two bulk phases of oil and water after 3 months. However, emulsion stability is greatly enhanced with the addition of LDH or Laponite particles. This synergism was accounted for by an increase of the dilational viscoelasticity modulus of the oil-water interface after particles were added to the aqueous phase. This increase indicates that the gel-like particle layer stays at the oil-water interface and resists emulsion coalescence. Scanning electron microscope (SEM) images display the presence of a firm layer surrounding the emulsion droplets and a three-dimensional particle network which extends into the bulk phase aiding emulsion stability.
通过将含有山梨糖醇油酸酯(Span 80)的油相和含有层状双氢氧化物(LDH)颗粒或 Laponite 颗粒的水相进行均化,制备了液体石蜡-水乳液。虽然将 LDH 与 Span 80 组合可以得到油包水(w/o)乳液,但由 Laponite-Span 80 稳定的乳液无论 Span 80 浓度如何,始终是 o/w 型的。激光诱导荧光共焦显微镜图像表明颗粒被吸收在乳液表面,表明所有乳液都是由颗粒稳定的。颗粒稳定的乳液类型的差异可以通过比较颗粒接触角和油水界面张力来解释,这表明更多的 Span 80 分子被吸附在 LDH 颗粒上而不是 Laponite 上。显然,Span 80 使 LDH 颗粒变得更疏水,导致形成 w/o 乳液。还比较了乳液的长期稳定性。单独用 Span 80 稳定的乳液在 3 个月后完全分离成油和水两个 bulk 相。然而,加入 LDH 或 Laponite 颗粒会大大提高乳液的稳定性。这种协同作用是由于添加颗粒后油水界面的拉伸粘弹性模量增加所致。这种增加表明凝胶状颗粒层停留在油水界面上并抵抗乳液聚结。扫描电子显微镜(SEM)图像显示在乳液液滴周围存在坚固的层和延伸到散装相的三维颗粒网络,有助于乳液稳定性。
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