Hands-on Activity: Investigating Contact Angle
Educational Standards :
Pre-Req Knowledge (Return to Contents)
Familiarity with surface tension, cohesive forces and adhesive forces, as explored in previous lessons in this unit.
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
Each group needs:
To share with the entire class:
Introduction/Motivation (Return to Contents)
(Begin with the associated lesson, and its Introduction/Motivation talk, to set the stage for conducting this activity with students. The lesson provides images and background information on contact angle, wetting, hydrophilic or hydrophobic surfaces. As necessary, refresh with the following questions to students:)
The way water interacts with the surface of an object influences the shape of the water droplets and can have important consequences. In today's lab, you will learn more about different surface coatings and their uses. First, let's review:
Today, we will explore the differences between water-loving (hydrophilic) and water-hating (hydrophobic) surfaces and how we can use this information to create products that make driving safer.
Procedure (Return to Contents)
These are suggested procedures, which you may need to alter, depending on student level, time constraints, and availability of materials.
Before the Activity
With the Students
Divide the class into lab groups and send them to the lab stations. To guide their lab investigations, hand out the worksheets, which include instructions and procedures, tables to record data and observations, and questions to answer as they go.
A. Observing Surface Coatings
B. Increasing Visibility in a Rainstorm
C. Anti-Fogging Properties
Attachments (Return to Contents)
Safety Issues (Return to Contents)
Troubleshooting Tips (Return to Contents)
It is best to wear gloves when handling coated glass. The oils from your hands eventually destroy the surface coating effects.
Assessment (Return to Contents)
Opening Questions: Have students write on note cards their answers to the questions, below. They can answer individually or work with a partner.
Activity Embedded Assessment
Activity Questions: Students demonstrate their thought processes during the activity by answering the questions on the Investigating Contact Angle Worksheet. Students extend their learning to real-world engineering problems, such as:
Gauge student comprehension by circulating throughout the classroom, asking students how they answered certain worksheet questions.
The Charges of Water Worksheet: To compare the strength of electrical forces between particles to the structure of substances at the bulk scale, have students complete The Charges of Water Worksheet, either in class or as homework. For more information on how the molecules in Rain-X® repel water, visit: "The Science of Rain-X" at http://hydrophobicsam.blogspot.com/2012/03/science-of-rain-x.html.
Web Search: Either in class or for homework, assign students to look online for products that claim to be either hydrophobic or hydrophilic. For each product found, answer the following questions:
Activity Extensions (Return to Contents)
Study the self-cleaning lotus effect using a piece of lotus leaf (dried lotus can be purchased in Asian grocery stores), another type of superhydrophobic leaf, or a self-cleaning fabric such as Nano-Tex™. Find information and lab activities for superhydrophobic surfaces in the Superhydrophobicity - The Lotus Effect lesson.
Additional Multimedia Support (Return to Contents)
Assign a student group to research new polymers created by chemical engineers that result in super slick surfaces useful for a multitude of medical, technical and industrial applications. Start with the National Science Foundation's website, "New Non-Stick? Many Uses Possible From "Squeezed" Molecules," at http://www.nsf.gov/od/lpa/news/press/00/pr0095.htm.
References (Return to Contents)
de Gennes, Pierre-Gilles. "Wetting—Statics and Dynamics." Reviews of Modern Physics, American Physical Society. 57 (1985): 827-863. Accessed September 1, 2010. http://rmp.aps.org/abstract/RMP/v57/i3/p827_1
de Gennes, Pierre-Gilles, et al. Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves. New York, NY: Springer, 2004. (Engineering connections.)
ContributorsJean Stave, Durham Public Schools, North Carolina, Professor Chuan-Hua Chen, Mechanical Engineering and Material Science, Pratt School of Engineering, Duke University, Jonathan Boreyko, Mechanical Engineering and Material Science, Pratt School of Engineering, Duke University
Copyright© 2011 by Mechanical Engineering and Material Science, Pratt School of Engineering, Duke University
This digital library content was developed under an NSF CAREER Award (CBET- 08-46705) and an RET supplement (CBET-10-09869).
Supporting Program (Return to Contents)NSF CAREER Award and RET Program, Mechanical Engineering and Material Science, Pratt School of Engineering, Duke University
Last Modified: December 11, 2013