Fotografiert mit dem iPhone 6

I began my PhD by studying silk electrogels; gels that are made by running a DC current through a solution of silk protein. We published a paper to show that the rheological properties of these gels are pretty impressive – super stretchy, and they get stronger as you pull them.

I finally got around to taking a video of gelation, which I purposefully captured with my iPhone so that I could recreate the Apple catchphrase I saw on a billboard in Munich.

The positive electrode is on the left, and a DC potential of 25 V is held across the ~2 cm sample length. As current flows through the reconstituted silk sample, electrolysis of water at the electrodes creates an acidic domain near the positive electrode, and a gel front propagates while bubbles form at the negative electrode on the right. Images are acquired every 30 seconds for a total of 15 minutes.

The fact that reconstituted silk solutions form a gel in the acidic environment created by electrolysis has led us to investigate the effects of silk solutions in the presence of HCl. It turns out that the effects of HCl alone are not exactly the same as the electric field! The differences between the two systems likely comes from either the migration of ions along the field lines or by reaction kinetics. The paper studying HCl effects will be published soon.