59th Annual Report on Research 2014

Progress on work funded by this grant in 2013--14 included: 1. Publication of a paper "Ultrasonic attenuation and speed of sound of cornstarch suspensions", Journal of the Acoustical Society of America 133, 1399 (2013) by B. Johnson (a graduate student supported by the grant (this paper reports a portion of his thesis work), M. Holland (a Physics Department researcher), and the co-P.I.s, J. G. Miller and J. I. Katz. This work measured the sound speed and attenuation as functions of ultrasonic frequency an starch concentration. From these data we determined the bulk modulus of corn starch granules (not determinable in any other manner) and constrained the attraction and clumping of these granules. 2. Publication of a paper "A mean field model of layering instability in shearing suspensions", Physical Review E (Rapid Communication) 89, 021003 (2014) by J. I. Katz (co-P. I.) that formulates a general theory of the layering of suspended particles into planar sheets that is responsible for the ubiquitous phenomenon of shear thinning. The layering was discovered by R. Hoffman in 1973, but no general theory, applicable to non-interacting (generally larger particles, like starch granules, rather than colloids) suspended particles had been known. 3. A paper "Hysteresis and lubrication in shear thickening of cornstarch suspensions", arXiv:1405.7233, by C. E. Chu (undergraduate), J. A. Groman (researcher supported by this grant), H. L. Sieber (undergraduate), J. G. Miller (co-P.I.), R. J. Okamoto (WU researcher) and J. I. Katz (co-P.I.) has been submitted to Physical Review E. It reports a program of rheological measurements of concentrated cornstarch suspensions, finds remarkable hysteresis of their characteristic discontinuous shear thickening, and explains many of their properties, including the long-known fact that their suspensions in non-polar solvents do not shear stiffen, as a result of the differing lubricities of the solvents. 4. A paper "Rheology in the teaching lab: properties of starch suspensions" by J. A. Groman (researcher supported by this grant), J. G. Miller and J. I. Katz (co-P.I.'s) is in preparation. This describes a very simple rheometer, involving the descent of a metal rod into a vertical cylinder filled with suspension, that is suitable for construction and use in the teaching lab, but that produces research-quality results within its domain of application.