Oil and Water
Oil and water don't mix. A chemical engineer would say oil is hydrophobic, or not attracted to water. Oil is also usually less dense than water, so it floats.
If you put a few drops of oil into a pan of water, the oil will stick together in small pools on the surface of the water. Even if you stir the water, the oil will return to the surface or cling to the sides of the tray rather than mix into the water.
Oil in water behaves differently if you add a surfactant. This is a compound that lowers the surface tension between the 2 liquids, allowing the oil to break down in very small droplets than can then be dispersed through the water. A dishwashing liquid can act as a surfactant.
If you add a drop or two or dishwashing liquid to your tray of water with the floating pools of oil, you'll notice that first, the oil spreads out - away from the detergent. But if you stir the water again the oil no longer pools - it becomes small droplets that stay suspended in the water.
These properties of oil create some unique challenges and opportunities when oil and water meet in the environment.
Oil Spill: Environmental Hazard!
Oil spills in the ocean damage and sometimes destroy wildlife and fragile ecosystems. Engineers work to design drilling and transport technology to prevent spills, but accidents happen. When they do, engineering is critical to stopping, containing, and cleaning up the mess.
What materials could you use to create an oil boom? How might you decide the best material for containing the spill? What materials would work best for absorbing the oil? Try to use a mix of materials so that your oil boom can do both.
- Cotton balls
- Gauze pads
- Pieces of rags
- Popsicle sticks
- Craft foam
- Napkins or paper towels
- Small plastic bottles, caps, or containers
- Aluminum foil
- Fishing bobbers
- Paper boats
When using materials around the house, you may want to test your materials. Do they float? Do they absorb water and/or oil? How can individual pieces be connected?