Tension-induced straightening transition of self-assembled helical ribbons.

Helical ribbons with pitch angles of either 11 degrees or 54 degrees self-assemble in a wide variety of quaternary surfactant-phospholipid/fatty acid-sterol-water systems. By elastically deforming these helices, we examined their response to uniaxial forces. Under sufficient tension, a low pitch helix reversibly separates into a straight domain with a pitch angle of 90 degrees and a helical domain with a pitch angle of 16.5 degrees. Using a newly developed continuum elastic free energy model, we have shown that this phenomenon can be understood as a first order mechanical phase transition.