Physics Department Colloquium: Eye patches: The Evolution of Novel Soft Matter

Wed, 09/13/2017 - 16:00 - 18:00
Alison Sweeney (U of Penn)

Life on Earth constitutes the most sophisticated iterations in the known universe of what physicists classify as soft matter.  Research in my group focuses on learning the physical rules of soft matter self-assembly phenomena via the evolutionary processes by which they arose over Earth’s history.  In this view of life as soft matter, evolution, with its own formal rules and algorithms, governs the appearance and diversification of novel forms of soft matter.  The field of soft matter was until very recently restricted to analytical consideration of simpler systems like isotropically interacting colloids and cross-linked polymers such as rubber. Our approach allows us to understand soft materials in a nuanced manner that would be inaccessible from more top-down analytical approaches.  In this colloquium, I will present the most detailed test case of this perspective to date: the evolutionary appearance of spherical, gradient-index lenses in squids.  This complex optical material, first described in theory by Maxwell in 1854, emerges from 5-nm spheroidal proteins via patchy colloidal physics.  The lens requires stable, transparent materials throughout the span of packing fractions (from near zero to near one); accordingly, the lens proteins exploit the entire patchy colloidal phase space, and our work is the first demonstration of many of these colloidal organizations in nature.  The self-assembling squid proteins exhibit structural nuances that have also been predicted by self-assembly theories, such that the evolved system may provide helpful insight to engineers designing systems at similar length scales.  Conceptually related projects such as the structure and function of quasi-ordered optics for camouflage of midwater squid eyes will also be discussed.

David Rittenhouse Laboratory - A8