DESIGNING PARTICLE SHAPES TO PASSIVELY TUNE SUSPENSION RHEOLOGY
Sinai Borker, Neeraj Nitin
This thesis concerns with the ability to change the properties of particle suspensions in a low Reynolds number simple shear flow over two orders of magnitude by designing shapes of the individual particles. The motion of particles such as rings with sharper outer edges, fibers with non-circular cross-sections or ramified particles can display unusual dynamics by small changes in their respective particle geometries. This work specifically focuses on particles that attain an equilibrium orientation without application of external forces or torques. Rheological properties of a suspension of such self-aligning particles (SAPs), such as intrinsic viscosity, hydrodynamic diffusivity and orientational dispersion, as a function of the particle aspect ratio display a phase transition-like behavior where the value of each of the rheological property drops by an order of magnitude near a critical aspect ratio A*. Using suspension of SAPs, rheological properties such as viscosity can be controlled by small changes in the particle aspect ratio; by adding a small number of tumbling particles to the suspension; or by varying the absolute particle, shear rate and/or the underlying fluid viscosity. This tunability of macroscopic properties of particle suspensions via passive control of the motion of its individual constituent particles opens new opportunities to fabricate functional materials with tunable properties using current processing flow technology such as injection molding or spin casting. A computationally inexpensive boundary element method for axisymmetric particles and a slender body theory accounting for cross-sectional effects on the force distribution of slender filaments, both in any linear flow fields, were developed as part of this thesis. These tools were used to obtain the motion of individual particles with exotic shapes. The suspension rheology was obtained through Brownian dynamics simulations and numerical calculations accounting for pairwise far-field hydrodynamic interactions and along with collisions. The shear rheology of rotating rings was also investigated to demonstrate its differences from the rheology of rotating fibers and discs. With the advancement in manufacturing techniques, self-aligning particle geometries can be accessed using fabrication methods such as 3D printing or lithography thereby allowing for experimental verification of our results and fabrication of functional materials.
Geometry; Rheology; Self-aligning particles; Shear flow; Slender body theory; Suspensions
Koch, Donald L.
Kirby, Brian; Stroock, Abraham Duncan
Ph. D., Mechanical Engineering
Doctor of Philosophy
dissertation or thesis