This Major Research Instrumentation Grant for Rapid Response Research (MRI-RAPID)award will be used to acquire an automatic microscopic contact angle meter (Kyowa MCA-3) for use in evaluating the wetting behaviors of small oil droplets of the kind typically found in the oil/water dispersions created in the Gulf oil spill. The quantitative characterization of these wetting behaviors is critical to both the evaluation of the effectiveness of natural wicking materials and the design of synthetic materials for both oil absorption and oil/water separation. The equipment is highly specialized to create oil droplets down to 20 microns in diameter and measure their contact angles when wetting low surface area, nonplanar materials, such as individual hairs or fibers. The speed of measurement is sufficient to obtain accurate contact angles even for droplets with high vapor pressures (evaporation rates), such as oil. The availability of such a capability will enable the rapid screening of potential oil wicking and separation materials that are being considered for use in the Gulf oil spill and will also serve the long term pursuit of a fundamental theory of surface wetting and two-phase fluid separation.
Numerous materials, from animal hair to cotton, corn husks, feathers and hay have been proposed for mopping up Gulf oil. The time and cost of evaluating these options experimentally would be enormous, making a quick, laboratory scale evaluation based on fundamental surface interactions a potentially critical resource. The equipment may well enable such an evaluation.
This research objective of this award is rapid and quantitative assessment of innovative materials for droplet retention from mixed oil/water emulsions. The research approach was to control liquid wetting behavior and transport oil/water droplets in different directions, through the combination of surface properties and nanostructures, such as . Our study lead to development of theoretical models that connect geometry and surface morphology to guide development of low-cost and scalable manufacturing process for optimization of oil collection and recovery materials. The outcome of this project includes: -The dynamic wetting behavior of a set of artificial spider silk fibers with varying knot size and periodicity is studied using the acquired MCA system with high resolution and high speed image capture and analysis for droplet spreading. We also observed the directional spreading effect at real time using the system, which is compared with thermodynamic modeling of asymmetric surfaces. - The dynamic behavior of impinging droplets and phospholipid films on different porous surface (such as membranes) is studied in real time using this setup, allowing determination of the effect of local micrometer scale surface features on wetting phenomena. In addition the measurement of wettability of single and multi-layered graphene sheets are performed, enhancing our understandting of the contact angle evolution and hysteresis of water droplets on graphene. Through the project we disseminated our findings to community through conference presentations and invited talks, and we offered lab tours to high school students from Boston area, and hosted several undergraduate students and international scholars to conduct summer research using the system.
