We are interested in uncovering the similarities and differences between conventional fluids, granular fluids, and active fluids. Each of the projects below addresses these ideas on a different length scale — micron, millimeter, and centimeter — and is powered either externally, internally, or not at all.
Flow-stabilized solids (FSS) are a class of fragile matter that forms when a dense suspension of colloids accumulates as it flows against a semi-permeable barrier in a micron-sized Hele-Shaw cell. In collaboration with the Riehn Group, we have observed that FSS form above a critical flow rate: this corresponds to to a situation in which the thermal fluctuations are insufficient to destabilized the pile. Our current investigations focus on how these effects are modified by size, shape, and particle-activity. Current researchers: Scott Lindauer
- Carlos P. Ortiz, Robert Riehn, Karen E. Daniels. “Nonaffine deformation under compression and decompression of a flow-stabilized solid.” Journal of Statistical Mechanics. 084003 (2016) [Link] [PDF]
- Carlos P. Ortiz, Karen E. Daniels, Robert Riehn. “Nonlinear Elasticity of Flow-Stabilized Solids.” Physical Review E 90: 022304 (2014) [Link] [PDF]
- Carlos P. Ortiz, Robert Riehn, and Karen E. Daniels. “Flow-Driven Formation of Solid-like Microsphere Heaps.” Soft Matter, 9 (2), 543 – 549, (2013) [Link] [PDF]
Baking flour will rest in a solid, stable heap on a table. However, when active particles such as flour beetle larvae (Tribolium confusus) are introduced into the flour, the mixture begins to slowly flow as a liquid. We are quantifying how the local wriggling of larvae generates viscous-like behavior at the bulk scale. To quantify the small-scale wiggliness of the larvae, we use Diffusing Wave Spectroscopy (DWS), which we then connect to the large-scale motions of the “fluid”. Current researchers: Emily Brown
In collaboration with Marcel Workamp and Joshua Dijksman (U. Wageningen), we are performing experiments on active-spinners. These particles draw their power from an air table base. Undergraduate researchers Mika Murphy and MRSEC-REU student Gustavo Ramirez have worked on this project.
- Marcel Workamp, Gustavo Ramirez, Karen E. Daniels,Joshua A. Dijksman. “Symmetry-reversals in chiral active matter.” [Preprint]