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. / Master of Science / Water shortage is one of the highest concerns all around the world and collecting fog water has drawn lots of attention recently. The focus of this thesis is to increase the fog collection rate by using less hazardous, low maintenance and low-cost methods. Commonly used fog collector is a large vertical plastic mesh. However, those large meshes suffer from water pinning and easily evaporation issues. Water repellent chemicals have been studied and used to dissolve those issues, however, the chemical coating will not last long and it will contaminate the collected water easily. Moreover, coating the water repellent chemicals requires professional operation and maintenance. To solve this issue without using chemical coating, we have learned unique water collection and directional behavior from spider silk. In a humid day, you will easily find the spider web with fully covered water droplets in an organized order. If we zoom in on single spider silk, the spider silk is composed of many puff and joint regions. Those puff regions have higher water collection ability than the joint regions, and this puff region shrinks down to form the spindle-knot shape with angle β above the joint region. This unique spindle-knot structure induces the water directional movement, and three forces- surface tension force, pinning force, and Laplace pressure force – are controlling the moving direction. Chapter 1 shows equation derivations with surface material effects, surface roughness effects and water droplet landing location effects. To form such special spindle-knot structure, commonly used formation methods are fluid coating and dip coating by using an organic polymer solvent. However, commonly used organic polymer-solvent suffer from a high level of hazardous, resulting in high laboratory requirement and operation cost. In Chapter 2 of this thesis, that commonly used organic polymer-solvent will be replaced by water/ethanol mixture and light-sensitive materials to form the spindle-knots. Furthermore, the 3D printing method is adopted to build a spider web with spindle-knot structures.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96610 |
| Date | 29 January 2020 |
| Creators | Cen, Yijia |
| Contributors | Mechanical Engineering, Cheng, Jiangtao, Ellis, Michael W., Zheng, Xiaoyu |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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