September 17, 2019
An acoustic sign can management the viscosity in shear-thickening supplies, which have potential makes use of as influence absorbers.
P. Sehgal/Cornell College
Sure gels and pastes develop into way more viscous when a load is utilized to them. This so-called shear thickening might be helpful in shock absorbers or delicate physique armor, the place one desires a fluid substance to stiffen on the on the spot of an influence. Nevertheless, the high-viscosity state is usually a nuisance in the course of the manufacturing course of, as it might probably result in jamming or clogging of kit. Prateek Sehgal and colleagues from Cornell College, New York, have discovered a method to management shear thickening with vibrations. By making use of acoustic perturbations to a particle-filled answer, the group was capable of scale back the viscosity by an element of 10.
Shear thickening happens in lots of widespread supplies, together with cement and a cornstarch-water concoction known as oobleck. These substances encompass small particles, similar to spherical grains or lengthy polymers, that usually move round one another. Nevertheless, when the fabric experiences a shear stress, among the particles lock collectively in a community of “drive chains,” inflicting as a lot as a 100-fold improve within the materials’s viscosity.
Earlier makes an attempt to regulate shear thickening have relied on altering the make-up of the fabric, which might adversely have an effect on the properties of the ultimate product. For that reason, the Cornell group pursued an “on-demand” technique for lowering viscosity that makes use of vibrations to interrupt the drive chains. The group examined their concept on a suspension of micrometer-sized silica particles positioned between two parallel plates. The highest plate turned to create shear, whereas a piezoelectric system hooked up to the underside plate generated vibrations at a frequency of round 1 MHz. This acoustic sign brought on the viscosity of the suspension to drop, typically all the way down to its zero-shear viscosity stage.
This analysis is revealed in Bodily Assessment Letters.
Michael Schirber is a Corresponding Editor for Physics primarily based in Lyon, France.
Supplies ScienceSoft Matter