Shear thickening fluids like mixtures of cornstarch and water, or oobleck, are not only fun to play with but also have applications ranging from 3D printing to body armor and shock absorption. However, the rapid increase in the viscosity with the shear rate, the very property that makes these suspensions so interesting for industrial applications also leads to jamming and failure of processing equipment. Thus, it is essential to find a method to control and tune the viscosity of these shear thickening suspensions. Here we discuss the various methods that we are working on to tune the viscosity of these shear thickening suspensions.
Understanding the flow of complex fluids through confined spaces and forces governing the flow is key to diverse fields, from blood flow to lubricant design. Studying such situations is difficult because typical devices cannot achieve the necessary degree of confinement. New experiments and simulations reveal flow behavior under different levels of confinement and show how this behavior can be tuned.
Microscopy is the workhorse of the physical and life sciences, producing crisp images of everything from atoms to cells well beyond the capabilities of the human eye. However, the analysis of these images is frequently little better than automated manual marking. Here, we revolutionize the analysis of microscopy images, extracting all the information theoretically contained in a complex microscope image.
Did you know that your brighfield or confocal microscope can actually measure stresses in colloidal materials? Here we introduce our SALSA (Stress Assessment from Local Structrure Anisotropy) method determining the stresses in hard-sphere colloidal suspensions. By just using the particle positions, SALSA can effectively transform your micorscope into a local pressure gauge.
We introduced an experiment to solve the mystry of how Oobleck works.
Why do some materials grow near-perfect crystals with mirror-smooth faces whereas others grow rough, bumpy crystals? Our group has recently gotten a glimpse of crystal growth in real time — not by watching individual atoms, but rather by freezing model atoms that can be observed directly with an optical microscope.
Colloidal suspensions – where micro-size or nano-size particles are suspended in a fluid – exhibit various equilibrium structures ranging from face-centered and cubic-centered crystals to binary ionic crystals, and even kagome lattices. When driven out-of-equilibrium by shear, even more diverse colloidal structures can be accessed. These structures lead to unique flow behaviors of suspensions.
In thermal equilibrium, particles suspended in a fluid randomly move about due to kicks from the fluid molecules, in what is known as Brownian motion or diffusion. Shear a fluid, however, and the particles' diffusion will be greatly enhanced. Why? Diffusion spreads some of the particles to regions of the fluid with different velocities. As the fluid then carries different particles with different speeds, the particles spread out faster, effectively increasing the diffusion. This mechanism, dubbed Taylor dispersion after its discoverer G. I.