Pradeep Kumar Sow

An Alternative Approach to Evaluate the Wettability of Carbon Fiber Substrates

The wettability of carbon fiber substrate plays an important role in a vast number of electrochemical energy production and storage technologies. Here, we report an alternative approach to evaluate the relative wettability for three substrates with the solid-liquid (S-L) interfacial area as the wettability parameter. We applied electrochemical techniques to quantify the S-L interfacial area and obtained the relative wettability on for three substrates with varying fiber morphology. This work proposes and validates a methodology to experimentally measure the substrate wettability and elucidates important aspects of the relevant wetting phenomena. Our results indicate that the wettability of carbon fiber substrate is affected by the liquid intrusion resulting from the instability of the Cassie-Baxter wetting state and that the contact angle is not dependent on the S-L interfacial area under the droplet. The present technique can be used to characterize the surface wettability of a wide range of conductive surfaces with irregular and multiscale surface roughness features.

Understanding the wettability of rough surfaces using simultaneous optical and electrochemical analysis of sessile droplets

The interaction of a droplet with a solid surface is characterized by two parameters, the contact angle and the wetted area under the droplet. The Cassie-Baxter and the Wenzel modes make predictions on the interfacial area by comparing the contact angles on smooth surfaces (the intrinsic wettability) with those on rough surfaces (the apparent wettability). In these models, the actual wetted area is used as a fitting parameter. In this work, we highlight the significance of determining the actual wetted area under the droplet and the limitation of using only the contact angle to represent the wetting behavior of a surface. Our experimental studies were performed on hydrophilic carbon surfaces where a combination of optical measurements (contact angle and hysteresis) along with an electrochemical approach was employed. An electrochemical method was used to determine the true wetted area using a droplet of aqueous electrolyte on the surface. The interfacial area was then used to correlate wetting behavior to that of the model predictions. We examined the impact of electrolyte concentration and potential sweep rate in our evaluation of the wetted area. Our results show that, for a rough hydrophilic surface, the decrease in contact angles with increasing solid-liquid interfacial areas is not always valid, as generally predicted by the Wenzel and the Cassie-Baxter models.