Grad Life

D-Lab at Stanford Splash


Michelle and our tray of water beads! Can you see them?

A couple weekends ago, Michelle, Alice, and I taught at Stanford Splash! Stanford Splash is a bi-annual weekend event that invites local 7th-12th graders to come to campus and take “classes” from Stanford students. The classes are usually on topics students might not be able to see in a regular high school, and range from academic topics like quantum mechanics and neuroscience, to non-academic stuff like hip hop dancing, origami, and listening skills. D-Lab was well represented: Michelle and I co-taught a science of invisibility class, I taught a class on some science stories around the color blue, and Alice co-taught a fun puzzle solving walk-in class, which featured invisible ink and microscopic clues!

Michelle and I came up with the “Science of Invisibility” class last fall, and we had such a fun time teaching that we decided to teach it again this spring. I really enjoy going through all our demos with the students as it makes the class much more interactive. One of the demos is my favorite demo from undergrad: the disappearing beaker trick. If you place a Pyrex beaker in a glass of oil, the beaker is visible, but once the inside beaker fills up with oil, it disappears! Since Pyrex glass and vegetable oil have very similar indices of refraction, light rays barely refract, or bend, at their interface, so to us, they look like the same material.

We also went through a similar demo which gave students a more hands-on experience. We submerged some clear water beads, which are these spherical hydrogels used in craft projects, in a clear glass of water and gave it to each student to explore. Why are the water beads visible in air, but not in water? What happens when you put them in a glass of oil? Next Splash, we’re thinking of also bringing food coloring, and having them think about what happens when you place them in colored water.


The bright blue iridescence of the marble berry, or Pollia condensata. Taken from S. Vignolini, et al. PNAS (2012)

In addition to my class with Michelle, I also taught a class which revolved around some science stories about the color blue. One of the topics I discussed was the origin (and lack of) blue in nature. Blue pigments are quite rare, and it turns out that the bright blue colors we see in animals like peacocks, blue jays, and butterflies are actually from periodic nanostructures that preferentially reflect blue light, something we call structural coloration. In researching for my class, I also learned about the marble berry, an inedible, metallic blue, berry-like fruit from Africa which also gets its iridescent sheen from structural coloration. It’s blue color is apparently one of the most intense out of all biological materials. 


A SEM image of a tiny clue, courtesy of Brian

Alice and her friend Johanna developed a series of puzzles including sudoku, crosswords, and connect the dots, which would ultimately solve a cipher for their puzzle solving hunt/mystery/class. They went all out to give the students a fun puzzle solving adventure, complete with invisible ink and microscopic clues. Brian even FIB-ed a message for them that was only 100 microns in size, or about the width of an average human hair!

Despite the (unusual) rain, it was a fun weekend and I really enjoyed sharing some topics in optics and science that I find so fascinating. It was also a great exercise in teaching; after getting some comments last time about the math being too hard, Michelle and I brainstormed about how to explain Snell’s Law accurately without alienating those who hadn’t seen some of the math concepts before. And, as an extra bonus, Michelle and I made too many water beads, and so they were put to good use in an epic office water bead fight – it’s really satisfying to see them explode!


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