Yang Angela, McKenzie Brian E, Pavlat Benjamin, Johnson Eric S, Khair Aditya S, Garoff Stephen, Tilton Robert D
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
The Procter & Gamble Company, Cincinnati, Ohio 45241, United States.
Langmuir. 2024 May 14;40(19):10143-10156. doi: 10.1021/acs.langmuir.4c00431. Epub 2024 May 1.
When placed in an ionic surfactant gradient, charged colloids will undergo diffusiophoresis at a velocity, = ∇ ln , where is the diffusiophoretic mobility and is the surfactant concentration. The diffusiophoretic mobility depends in part on the charges and diffusivities of the surfactants and their counterions. Since micellization decreases surfactant diffusivity and alters charge distributions in a surfactant solution, of charged colloids in ionic surfactant gradients may differ significantly when surfactant concentrations are above or below the critical micelle concentration (CMC). The role of micelles in driving diffusiophoresis is unclear, and a previously published model that accounts for micellization suggests the possibility of a change in the sign of above the CMC [Warren, P. B.; . 2019, 15, 278-288]. In the current study, microfluidic channels were used to measure the transport of negatively charged polystyrene colloids in sodium dodecyl sulfate (SDS) surfactant gradients established at SDS concentrations that are either fully above or fully below the CMC. Interpretation of diffusiophoresis was aided by measurements of the colloid electrophoretic mobility as a function of SDS concentration. A numerical transport model incorporating the prior diffusiophoretic mobility model for ionic surfactant gradients was implemented to elucidate signatures of positive and negative diffusiophoretic mobilities and compare with experiments. The theoretically predicted sign of the diffusiophoretic mobility below the CMC was determined to be particularly sensitive to uncertainty in colloid and surfactant properties, while above the CMC, the mobility was consistently predicted to be positive in the SDS concentration range considered in the experiments conducted here. In contrast, experiments only showed signatures of a negative diffusiophoretic mobility for these negatively charged colloids with no change of sign. Colloid diffusiophoretic transport measured in micellar solutions was more extensive than that below the CMC with the same ∇ ln .
当置于离子表面活性剂梯度中时，带电胶体将以速度 进行扩散泳动，其中 是扩散泳动率， 是表面活性剂浓度。扩散泳动率部分取决于表面活性剂及其抗衡离子的电荷和扩散率。由于胶束化会降低表面活性剂的扩散率并改变表面活性剂溶液中的电荷分布，因此当表面活性剂浓度高于或低于临界胶束浓度（CMC）时，离子表面活性剂梯度中带电胶体的 可能会有显著差异。胶束在驱动扩散泳动中的作用尚不清楚，先前发表的一个考虑胶束化的模型表明，在 CMC 以上 的符号可能会发生变化[沃伦，P.B.；. 2019 年，15 卷，278 - 288 页]。在当前的研究中，微流控通道被用于测量带负电的聚苯乙烯胶体在十二烷基硫酸钠（SDS）表面活性剂梯度中的传输，该梯度是在 SDS 浓度完全高于或完全低于 CMC 的情况下建立的。通过测量胶体电泳迁移率作为 SDS 浓度的函数，有助于对扩散泳动进行解释。实施了一个包含先前离子表面活性剂梯度扩散泳动率模型的数值传输模型，以阐明正、负扩散泳动率的特征并与实验进行比较。理论预测在 CMC 以下扩散泳动率的符号对胶体和表面活性剂性质的不确定性特别敏感，而在 CMC 以上，在此处进行的实验所考虑 的 SDS 浓度范围内，迁移率一直被预测为正。相比之下，实验仅显示这些带负电的胶体具有负扩散泳动率的特征，且符号没有变化。在胶束溶液中测量的胶体扩散泳动传输比在相同 但低于 CMC 的情况下更广泛。
