Research

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.

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.

Tsevi Beatus, John Guckenheimer and Itai Cohen, 
The Journal of the Royal Society Interface 12, 20150075 (2015) PDF

Articular cartilage (AC), a biological tissue that protects and lubricates joints, plays a critical role during healthy locomotion.  Ongoing work in the Cohen lab has been examining the spatially heterogeneous mechanical properties of this tissue using confocal rheology.  This technique allows us to simultaneously deform the tissue with a known stress and measure the local strain field.  From this information, we can calculate the local shear properties.

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.