Investigating Contact Angle
The water repellent treatment on this tight-weave fabric causes water to bead up and roll off. NOAA uses this tough material for its "smart balloons," which are launched into the atmosphere for hurricane research and weather measurement tasks.Copyright NOAA http://www.noaa.inel.gov/capabilities/smartballoon/smartballoon.htm
Students observe how water acts differently when placed on hydrophilic and hydrophobic surfaces. They determine which coatings are best to cause surfaces to shed water quickly or reduce the "fogging" caused by condensation.
Engineers who design liquids and/or whose products come in contact with liquids must understand the science of contact angles—a liquid's tendency to either bead or sheet on a solid surface—which is determined by the properties of both the surface and the liquid. The resulting hydrophilic ("water loving") and hydrophobic ("water hating") surfaces have important applications in all types of engineering, including chemical, automotive, nautical, industrial and civil engineering. A hydrophilic anti-fog coating on glass causes condensation to form into a thin, even layer of water instead of droplets, so the glass remains transparent. On a windshield with a hydrophobic rain-repellent glass treatment, water beads and rolls off the surface, improving visibility (and safety). Hydrophobic surfaces are also important in protecting surfaces from water damage and stains.
After this activity, students should be able to:
- Describe the behavior of water on hydrophobic and hydrophilic surfaces and explain in general terms what causes the differences in behavior.
- Discuss situations in which applying a hydrophilic or hydrophobic surface would be advantageous.