Fog Harvesting: Inspired by Spider Silk

The water crisis has been an increasing challenge in some places in the world. One proposed solution that has drawn lots of attention is fog harvesting. A commonly used fog collector is a vertical mesh, usually made of poly materials. Small water droplets can easily get pinned and quick evaporation is the major common challenge for vertical meshes. Coating the fog mesh with superhydrophobic chemicals is one of the solutions. However, superhydrophobicity is not durable and it may contaminate the collected water. In addition, it requires a high professional maintenance and laboratory operation standard. As a result, it is impractical to set such fog collectors in regions and countries with water crisis. Low cost, harmless, easily fabricated, higher coalesce rate and low maintenance are the five pillars for this research. This thesis topic is inspired by spider silk's ability to direct water droplets to certain locations to further enhance water collecting rate. This directional droplet movement is caused by spindle-knot and joint structure on the biomimetic silk. The spindle-knot is randomly porous, and the joint is stretched porous. In addition, the spindle-knot has a tilted angle β above the joint region. Due to these unique structures, there are three droplet movement controlling forces – surface tension force, hysteresis force, and Laplace pressure force. This thesis presents detailed equation derivations for each driving force in the introduction section. Spindle-knot is the pivot point to direct water, forming the spindle-knot structure is another focus of this thesis. Fluid coating and dip-coating with dimethylformamide (DMF), a solvent with a low evaporation rate, is the highly used methods to form the spindle-knot structures due to its simple setup and low cost. However, DMF is an extremely hazardous organic compound, and it requires high laboratory operation standards. In the second section of this thesis, DMF has been replaced with water/ethanol and photocurable materials to construct the spindle-knots. Furthermore, Additive manufacturing (3D printing method) was adopted to synthesize bionic spider web with spindle-knot structures.