Quantitative Correlation between Adsorbed and Condensed Water Mass with Response Galvanic Current Detected at the Micron Gap of Galvanic-Coupled Arrays

Abstract

Sensor surfaces with micron- and nano-gap scales possess high surface-to-volume ratio which greatly affects their contribution towards water adsorption and condensation. However, the quantitative relationship between adsorbed water molecules and condensed water droplets remains unclear. In this study, we used the humidity-based detected galvanic current within the micron gaps of our newly developed moisture sensor chip (MSC) to emphasize the quantitative relationship between adsorbed water molecules and condensed water droplets. The mass of adsorbed water molecules was detected using a quartz-crystal-microbalance electrode (QCM) whereas the mass of condensed water droplets was estimated microscopically based on their occupying volumes at MSC surface. Experimental results demonstrated that the minimum detection limit of MSC under these experimental conditions was ~150 ng/cm2 for adsorbed water molecules and ~700 ng/ cm2 for condensed water droplets. The detected-response galvanic current arises when a water bridges between two adjacent arrays is found to be linearly correlated to the adsorbed and/or the condensed water’s mass. Such correlation is believed to provide a feasible long-range sensor that can distinguish the status of its surface-existing water either in adsorbed molecular or condensed droplet-wise regimes.

Keywords

• adsorbed water molecules
• condensed water droplets
• moisture sensor chip (MSC)
• quartz crystal microbalance (QCM)