Author: Jennifer Tumlin
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358. This lesson is inspired by teachengineering.org's Curricular Unit: Surface Tension
The polar nature of water allows this molecule to carry out many important functions in living systems and the geochemistry of Earth. In this activity students will closely observe the behavior of water droplets to understand cohesion, adhesion, surface tension, and capillary action. Students will conduct contact angle measurements to quantify the wettability (hydrophilic, hydrophobic, or superhydrophilic nature) of surfaces. Through these investigations students will extend their understanding biomimicry and how the properties of water can be used to solve real-life problems.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
The teacher could wear a shirt with a comically conspicuous stain, one that students would comment on. Alternatively, just ask students what would happen if you poured a beverage or dropped your lunch on your clothing.
Tell students that in this lab activity they will learn about how to determine if a surface is waterproof or hydrophobic.
Show pre-lab instructions for measuring contact angle.
Students will conduct the lab activity with a partner.
Modifications: This activity can be conducted qualitatively. Students observe the drops by eye or with hand lenses to make a qualitative sketch of the drops. They can compare the shape of the drop to those illustrated in the pre-lab powerpoint instead of calculating the contact angle.
Teacher will conduct a formative assessment of students, making sure students are properly carrying out contact angle measurements and answering questions, ideally without the help of internet search engines.
Students will use observations and data collected during the activity to construct written, scientific explanations of the characteristics of water and surface chemistry.
Teacher will follow up lab with the post lab discussion powerpoint. This includes a review of the vocabulary and extension topic.
Extension discussion topics related to this can include: adaptations and natural selection, biomimicry, and engineering applications.
Extension activities could include testing commercially available coatings (Rustoleum Never Wet, car polishes, floor wax, silicone sprays, and hair cosmetics (anti-frizz and glossing serums) on glass slides, sandpaper, or Teflon tape or other materials. See images of these products and the contact angle data in the post lab powerpoint for teacher reference.
HS-PS2-6 Motion and Stability: Forces and Interactions
Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
HS-PS1-3 Matter and Its Interactions
Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Having an understanding of how water interacts in the environment (gardening, cleaning, etc.) and the use of everyday products that are hydrophobic.
Engineers are taking inspiration from nature (biomimetic thinking) to solve problems in the real world.