We report a new method for directly monitoring dynamic surface wetting that occurs during electrochemical droplet cell corrosion measurements on an Al alloy and Cu galvanic couple. The combination of a goniometer and potentiostat enabled the in situ observation of wettability during polarization of each metal and at the interface of the two metals in 0.4 μL NaCl aqueous droplets. Droplet spreading was heterogeneously dynamic for measurements at the interface of the two metals, where oxygen from the surrounding environment diffused into the droplet edges and reduced on the cathodic metal, thus increasing the wettability on this region, while the anodic metal served as a sacrificial anode and remained in a constant wetted state. Such dynamic wetting was inhibited by performing measurements under anaerobic conditions, where minimal changes in voltammetric response were observed in comparison the measurements performed in air. All voltammetry was normalized by the true surface area of the droplet footprint, which was measured after droplet evaporation to avoid overestimating corrosion current densities. This work highlights the potential for the combined goniometer-electrochemical setup to further enhance the corrosion community's knowledge about interfacial chemistry and the importance of considering the dynamic evolution of micro/nanoscale droplets on heterogeneous substrates when estimating corrosion rates.

我们报告了一种直接监测动态表面润湿的新方法，该方法在对铝合金和铜电偶进行电化学液滴电池腐蚀测量期间发生。测角仪和恒电位仪的结合使原位观察每种金属极化过程中以及两种金属在 0.4 μL NaCl 水滴界面处的润湿性。对于两种金属界面处的测量，液滴扩散是非均匀动态的，其中来自周围环境的氧气扩散到液滴边缘并在阴极金属上减少，从而增加了该区域的润湿性，而阳极金属充当牺牲阳极并保持恒定的湿润状态。通过在厌氧条件下进行测量来抑制这种动态润湿，与在空气中进行的测量相比，观察到伏安响应的最小变化。所有伏安法都通过液滴足迹的真实表面积归一化，这是在液滴蒸发后测量的，以避免高估腐蚀电流密度。这项工作突出了测角仪-电化学组合装置进一步增强腐蚀界对界面化学知识的潜力，以及在估计腐蚀速率时考虑异质基材上微/纳米级液滴动态演变的重要性。