Cationic surfactant coatings (e.g., CTAB) are commonly used in CE to control EOF and thereby improve separation efficiencies. However, our understanding of surfactant adsorption and desorption dynamics under EOF conditions is limited. Here, we apply automated zeta potential analysis to study the adsorption and desorption kinetics of CTAB in a capillary under different transport conditions: diameter, length, voltage alternation pattern and frequency, and applied pressure. In contrast to other studies, we observe slower kinetics at distinct capillary wall zeta potential ranges. Within these ranges, which we call “stagnant regimes,” the EOF mobility significantly counteracts the electrophoretic (EP) mobility of CTA⁺ and hinders the net transport. By constructing a numerical model to compare with our experiments and recasting our experimental data in terms of the net CTA⁺ transport volume normalized by surface area, we reveal that the EP mobility of CTA⁺ and the capillary surface-area-to-volume ratio dictate the zeta potential range and the duration of the stagnant regime and thereby govern the overall reaction kinetics. Our results indicate that further transport-oriented studies can significantly aid in the understanding and design of electrokinetic systems utilizing CTAB and other charged surfactants.

中文翻译：

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CTAB 的动电传输在毛细管吸附和解吸过程中诱导多相行为

阳离子表面活性剂涂层（例如 CTAB）通常用于 CE 中以控制 EOF，从而提高分离效率。然而，我们对 EOF 条件下表面活性剂吸附和解吸动力学的理解是有限的。在这里，我们应用自动 zeta 电位分析来研究毛细管中 CTAB 在不同传输条件下的吸附和解吸动力学：直径、长度、电压交替模式和频率以及施加的压力。与其他研究相比，我们在不同的毛细血管壁 zeta 电位范围内观察到较慢的动力学。在这些我们称之为“停滞状态”的范围内，EOF 迁移率显着抵消了 CTA ⁺的电泳 (EP) 迁移率并阻碍了净传输。通过构建数值模型与我们的实验进行比较，并根据表面积归一化的净 CTA ^{+传输体积重新构建我们的实验数据，我们揭示了 CTA +}的 EP 迁移率和毛细管表面积与体积之比决定了Zeta 电位范围和停滞状态的持续时间，从而控制整个反应动力学。我们的结果表明，进一步的以传输为导向的研究可以极大地帮助理解和设计利用 CTAB 和其他带电表面活性剂的动电系统。