Wilson Jessica L, Shim Suin, Yu Yingxian Estella, Gupta Ankur, Stone Howard A
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, United States.
Langmuir. 2020 Jun 30;36(25):7014-7020. doi: 10.1021/acs.langmuir.9b03333. Epub 2020 Mar 4.
Diffusiophoresis is the spontaneous movement of colloidal particles in a concentration gradient of solutes. As a small-scale phenomenon that harnesses energy from concentration gradients, diffusiophoresis may prove useful for passively manipulating particles in lab-on-a-chip applications as well as configurations involving interfaces. Though naturally occurring ions are often multivalent, experimental studies of diffusiophoresis have been mostly limited to monovalent electrolytes. In this work, we investigate the motion of negatively charged polystyrene particles in one-dimensional salt gradients for a variety of multivalent electrolytes. We develop a one-dimensional model and obtain good agreement between our experimental and modeling results with no fitting parameters. Our results indicate that the ambipolar diffusivity, which is dependent on the valence combination of cations and anions, dictates the speed of the diffusiophoretic motion of the particles by controlling the time scale at which the electrolyte concentration evolves. In addition, the ion valences also modify the electrophoretic and chemiphoretic contributions to the diffusiophoretic mobility of the particles. Our results are applicable to systems where the chemical concentration gradient is comprised of multivalent ions, and motivate future research to manipulate particles by exploiting ion valence.
扩散泳是胶体颗粒在溶质浓度梯度中的自发运动。作为一种利用浓度梯度能量的小规模现象，扩散泳在芯片实验室应用以及涉及界面的配置中被动操纵颗粒方面可能会很有用。尽管天然存在的离子通常是多价的，但扩散泳的实验研究大多局限于单价电解质。在这项工作中，我们研究了多种多价电解质在一维盐梯度中带负电的聚苯乙烯颗粒的运动。我们开发了一个一维模型，并且在没有拟合参数的情况下，实验结果与建模结果取得了良好的一致性匹配。我们的结果表明，双极性扩散率取决于阳离子和阴离子的价态组合，通过控制电解质浓度变化的时间尺度来决定颗粒扩散泳运动的速度。此外，离子价态还会改变颗粒扩散泳迁移率的电泳和化学泳贡献。我们的结果适用于化学浓度梯度由多价离子组成的系统，并推动了未来通过利用离子价态来操纵颗粒的研究。
