Monica Ripp and Jikai Wang gave successful PhD defenses this year. Monica’s dissertation, “Buckling Patterns and Mechanics of Thin Interfacial Polymer Films,” was defended on October 15, 2021. Jikai’s dissertation, “Self organization in models of cyclically-sheared suspensions,” was defended on April 2, 2021. Congratulations, Jikai & Monica!
Our group recently had a manuscript published in Physical Review Letters, titled: “Sculpting Liquids with Ultrathin Shells”. Co-authors are postdocs Yousra Timounay and Mengfei He, former SU undergrad Lindsay Murphy, REU student Alex Hartwell, grad student Eric King, and collaborator Prof. Vincent Démery (ESPCI Paris). Our work shows how an ultrathin shell can “sculpt” a liquid interface into its own shape, through a mechanism that is much like the inflation of a stiff balloon.
Consider for a moment the smooth wrinkles on our skin and the sharp creases on a crumpled ball of paper. These two kinds of surfaces look and feel quite different, and you might wager that the difference comes down to the material itself: skin makes “wrinkles” and paper makes “crumples”. We found that this reasonable guess is actually wrong. By squeezing and inflating plastic and rubber sheets in a variety of experiments, we discovered how to turn wrinkles into crumples and then back. What’s more, we found that crumples are rather general features — nature uses this “building block” to help sheets contort in a lot of geometrically-tricky situations. So understanding the physics of a birthday balloon can teach you things that are important for designing deployable satellites or understanding ripples in a cell membrane. Links: PRX, APS Physics Magazine
Thin sheets are easily bent and twisted into different shapes while staying within the linear elastic response of the material. Think of rolling up a scientific poster: large displacements occur with relatively small forces and virtually no damage to the material. Such geometric nonlinearities complicate the relationships between forces, deformations, and material properties for any slender material, from textiles to polymer capsules to flagella. We map out the surprisingly rich mechanical response of a floating polymer film to indentation, using experiments, simulations, and theory. Our geometric approach provides a new tool for understanding the mechanics of sheet-laden interfaces in general settings. Links: Soft Matter, arXiv
We are all familiar with the wrinkled texture of a raisin or a candy wrapper. Studying the arrangement of wrinkles in polymer films can lend insight into these and other materials that wrinkle, from textiles to biological tissues to synthetic skins. To address the complexity of wrinkle patterns, we asked the following basic question: “What happens when the direction of wrinkling is in direct conflict with the preferred wavelength?” Our answer is a quantitative framework for understanding the mesoscale organization of groups of wrinkles in such situations, with analogs to liquid crystals and superconductors. Links: PNAS, arXiv
The group welcomes postdoctoral researcher Mengfei He. Mengfei comes from the Nagel lab at the University of Chicago. Welcome, Mengfei!
Despite the ubiquity of memory formation in condensed matter, there is presently no overarching framework for classifying memory behaviors. This review article considers memory formation across a broad range of systems (memories in rocks, rubber, glasses, and amorphous solids; memories in magnetic systems; echo phenomena; shape memory; associative memory; etc.), with an eye towards developing unifying conceptual underpinnings for material memories. Such a study of memory formation provides a setting for exploring some of the most fascinating aspects of history-dependence, dynamics, and information storage in far-from-equilibrium systems.
We typically think of memory as the stuff stored in hard drives or our brains, but memory effects abound in a wide range of materials. Rubber and rocks can remember the largest load that was applied to them, glasses may remember a temperature where they were aged, and shape-memory alloys can recall a programmed shape. One approach to building a broader understanding of memory formation in matter is to construct and study simple models where memories may be written, stored, and retrieved. This article shows how a model of worn grass between park benches can produce a peculiar memory behavior that has been observed in the motion of electrons in a special kind of conductor, and in the flow of solid grains in viscous liquids. Continue reading “How much can a grassy path remember?”
REU student Jessica Stelzel has been awarded a National Science Foundation Graduate Research Fellowship. She will be starting her PhD at Johns Hopkins University in the Fall, working to create regenerative biomaterials with Dr. Hai-Quan Mao. Congratulations, Jessica!
paulsengroup 
Recent Comments