Hydrophobic Surfaces - A Love/Hate Relationship (Lisa Hellinger)

Author:

Lisa Hellinger

Principle(s) Illustrated:

Superhydrophobic Surfaces in Nature:

Commercial Applications of Superhydrophobic Surfaces:

• • "waterproofing" sprays for boots and clothes

  • hulls of racing boats are coated with superhydrophobic material to reduce drag

  • teflon coated frying pans prevent food from sticking

  • satellite dishes have coating to reduce build-up of rain or snow

Standards:

NGSS Science & Engineering Standards

• Constructing Explanations and Designing Solutions

  • Evaluate a solution to a complex real-world problem, based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and tradeoff considerations. (HS-ETS1-3)

NGSS Cross-cutting Concept Standards

• Types of Interactions

  • Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. (HS-PS2-6),(secondary to HS-PS1-1),(secondary to HS-PS1-3)

NGSS Disciplinary core idea standards

• Structure and Function

  • Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem. (HS-LS1-1)

Questioning Script:

Prior knowledge & experience:

• None

Root question:

• Why do water droplets behave differently on silver coated copper squares?

Target response:

• The surfaces are hydrophobic or hydrophilic due to different coatings. Droplet will spread out on a hydrophilic surface and will form a ball on a superhydrophobic surface.

Common Misconceptions:

• Oil and water are not attracted to each other.

  • They are, but the water to water attraction is much stronger than the oil to water attraction, so the water "sticks" together and does not allow the oil to mix. The Lehman Group at the University of Virginia helps make this easier to understand by likening oil and water to a high school dance - "One can make an analogy to a high school dance, where generally one will find that the most popular boys and girls will dance with each other almost exclusively. It is not that the less popular members of the class do not want to dance with the popular students, it is just that the popular students have their choice of who to dance with and, since they also want to dance with popular students, they pair off. The less popular students, rather than have no partners, will naturally pair off as well." http://www.faculty.virginia.edu/lehmannlab/badchemistry.html)

Materials & Procedures:

Materials:

• 4 copper squares per group

• 1 pair of forceps per group

• 1 pipette per group

• colored water

Procedures:

• Place a single drop of water on each copper square

• Record observations of how the water drop looks on each square

• Draw or photograph the drops from the side

Photographs and Movies:

References:

Superhydrophobic Surfaces Experiment