Mao Canwei, Soda Yoshiki, Robinson Kye J, Forrest Tara, Bakker Eric
Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, Switzerland.
ACS Meas Sci Au. 2022 Oct 4;3(1):45-52. doi: 10.1021/acsmeasuresciau.2c00053. eCollection 2023 Feb 15.
Recent work has shown that ion-selective components may be transferred from nanoemulsions (NEs) to endow polymeric membranes with ion-selective sensing properties. This approach has also been used for nanopipette electrodes to achieve single-entity electrochemistry, thereby sensing the ion-selective response of single adhered nanospheres. To this date, however, the mechanism and rate of component transfer remain unclear. We study here the transfer of lipophilic ionic compounds from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS) films by chronoamperometry and quartz crystal microbalance. Thin-film cyclic coulovoltammetry measurements serve to quantify the uptake of lipophilic species into blank PVCDOS membranes. Electrochemical quartz crystal microbalance data indicate that the transfer of the emulsion components is insignificant, ruling out simple coalescence with the membrane film. Ionophores and ion-exchangers are shown to transfer into the membrane at rates that correlate with their lipophilicity if mass transport is not rate-limiting, which is the case with more lipophilic compounds (calcium and sodium ionophores). On the other hand, with less lipophilic compounds (valinomycin and cation-exchanger salts), transfer rates are limited by mass transport. This is confirmed with rotating disk electrode experiments in which a linear relationship between the diffusion layer thickness and current is observed. The data suggests that once the nanoemulsion container approaches the membrane surface, transfer of components occur by a three-phase partition mechanism where the aqueous phase serves as a kinetic barrier. The results help better understand and quantify the interaction between nanoemulsions and ion-selective membranes and predict membrane doping rates for a range of components.
近期研究表明，离子选择性成分可从纳米乳液（NEs）转移，赋予聚合物膜离子选择性传感特性。该方法也已用于纳米移液器电极以实现单实体电化学，从而检测单个附着纳米球的离子选择性响应。然而，迄今为止，成分转移的机制和速率仍不清楚。我们在此通过计时电流法和石英晶体微天平研究亲脂性离子化合物从纳米乳液向薄增塑聚氯乙烯（PVC - DOS）膜的转移。薄膜循环伏安法测量用于量化亲脂性物质在空白PVCDOS膜中的摄取量。电化学石英晶体微天平数据表明乳液成分的转移不显著，排除了与膜简单聚结的情况。如果传质不是限速步骤，离子载体和离子交换剂会以与其亲脂性相关的速率转移到膜中，对于亲脂性更强的化合物（钙和钠离子载体）就是这种情况。另一方面，对于亲脂性较弱的化合物（缬氨霉素和阳离子交换剂盐），转移速率受传质限制。旋转圆盘电极实验证实了这一点，在该实验中观察到扩散层厚度与电流之间存在线性关系。数据表明，一旦纳米乳液容器靠近膜表面，成分转移通过三相分配机制发生，其中水相起动力学屏障的作用。这些结果有助于更好地理解和量化纳米乳液与离子选择性膜之间的相互作用，并预测一系列成分的膜掺杂速率。
