Park Bum Jun, Pantina John P, Furst Eric M, Oettel Martin, Reynaert Sven, Vermant Jan
Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA.
Langmuir. 2008 Mar 4;24(5):1686-94. doi: 10.1021/la7008804. Epub 2008 Jan 18.
The forces between colloidal particles at a decane-water interface, in the presence of low concentrations of a monovalent salt (NaCl) and the surfactant sodium dodecyl sulfate (SDS) in the aqueous subphase, have been studied using laser tweezers. In the absence of electrolyte and surfactant, particle interactions exhibit a long-range repulsion, yet the variation of the interaction for different particle pairs is found to be considerable. Averaging over several particle pairs was hence found to be necessary to obtain a reliable assessment of the effects of salt and surfactant. It has previously been suggested that the repulsion is consistent with electrostatic interactions between a small number of dissociated charges in the oil phase, leading to a decay with distance to the power -4 and an absence of any effect of electrolyte concentration. However, the present work demonstrates that increasing the electrolyte concentration does yield, on average, a reduction of the magnitude of the interaction force with electrolyte concentration. This implies that charges on the water side also contribute significantly to the electrostatic interactions. An increase in the concentration of SDS leads to a similar decrease of the interaction force. Moreover, the repulsion at fixed SDS concentrations decreases over longer times. Finally, measurements of three-body interactions provide insight into the anisotropic nature of the interactions. The unique time-dependent and anisotropic interactions between particles at the oil-water interface allow tailoring of the aggregation kinetics and structure of the suspension structure.
利用激光镊子研究了在癸烷 - 水界面处，水相亚相中存在低浓度单价盐（氯化钠）和表面活性剂十二烷基硫酸钠（SDS）时胶体颗粒之间的作用力。在没有电解质和表面活性剂的情况下，颗粒间相互作用表现出长程排斥作用，但发现不同颗粒对之间相互作用的变化相当大。因此，发现有必要对几个颗粒对进行平均，以获得对盐和表面活性剂影响的可靠评估。此前有人提出，这种排斥作用与油相中少量离解电荷之间的静电相互作用一致，导致相互作用随距离以 -4 次方衰减，且电解质浓度没有任何影响。然而，目前的研究表明，平均而言，增加电解质浓度确实会使相互作用力的大小随电解质浓度降低。这意味着水相一侧的电荷对静电相互作用也有显著贡献。SDS 浓度的增加会导致相互作用力类似地降低。此外，在固定的 SDS 浓度下，排斥作用在较长时间内会减弱。最后，三体相互作用的测量为相互作用的各向异性性质提供了见解。油水界面处颗粒之间独特的时间依赖性和各向异性相互作用使得能够调整悬浮结构的聚集动力学和结构。
