Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1205 Geneva, Switzerland.
Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1205 Geneva, Switzerland.
J Colloid Interface Sci. 2020 Apr 15;566:143-152. doi: 10.1016/j.jcis.2020.01.075. Epub 2020 Jan 21.
Homoaggregation and heteroaggregation involving amidine and sulfate latex particles in the presence of the anionic surfactant octyl sulfate (OS) is studied by light scattering. This surfactant causes a charge reversal of the amidine particles. This reversal induces a rapid homoaggregation near the charge reversal point. In the presence of the same surfactant, the sulfate particles remain negatively charged and stable. The heteroaggregation process is probed in mixed suspensions of amidine and sulfate latex particles with multi-angle time-resolved dynamic light scattering. This technique allows differentiating between the contributions of homoaggregation and heteroaggregation, and permits to measure the heteroaggregation rate. By optimally choosing the sizes of the particles, one can optimize the contrast and extract heteroaggregation stability ratio over a wide range. The heteroaggregation rate is fast at low OS concentrations, where the two particles are oppositely charged. This rate slows down at higher OS concentrations due to double layer repulsion between the negatively charged particles. However, the onset of this slow heteroaggregation occurs at lower OS concentrations than for homoaggregation. The reason for this shift is that the double layer repulsion between two OS-decorated amidine particles is weaker than between one sulfate particle and one OS-decorated amidine particle. These measurements compare favorably with calculations with the theory by Derjaguin, Landau, Verwey, and Overbeek (DLVO). These calculations suggest that constant potential boundary conditions are more appropriate than the ones of constant charge. In the system studied, the present light scattering technique permits to extract heteroaggregation stability ratios over almost three orders of magnitude. This study is the first of its kind, where such a large range is being probed.
通过光散射研究了在阴离子表面活性剂辛基硫酸盐（OS）存在下涉及脒基和硫酸盐乳胶颗粒的同聚和共聚。这种表面活性剂会导致脒基颗粒的电荷反转。这种反转在电荷反转点附近诱导快速同聚。在相同的表面活性剂存在下，硫酸盐颗粒保持带负电荷且稳定。通过多角度时间分辨动态光散射研究了混合悬浮在酰胺和硫酸盐乳胶颗粒中的共聚过程。该技术允许区分同聚和共聚的贡献，并允许测量共聚速率。通过最佳选择颗粒的尺寸，可以优化对比度并在较宽的范围内提取共聚稳定性比。在 OS 浓度较低的情况下，两种颗粒带相反电荷，共聚速率很快。在更高的 OS 浓度下，由于带负电荷的颗粒之间的双层排斥作用，该速率会减慢。然而，这种缓慢共聚的开始发生在比同聚更低的 OS 浓度下。这种转变的原因是两个 OS 修饰的脒基颗粒之间的双层排斥作用比一个硫酸盐颗粒和一个 OS 修饰的脒基颗粒之间的双层排斥作用弱。这些测量结果与由 Derjaguin、Landau、Verwey 和 Overbeek（DLVO）提出的理论计算结果非常吻合。这些计算表明，恒电位边界条件比恒电荷条件更合适。在研究的系统中，本研究采用的光散射技术可以在几乎三个数量级的范围内提取共聚稳定性比。这是首次在如此大的范围内进行此类研究。
