(334g) The Rheology and Dynamics of Soft Particles in Viscoelastic Flows Via Immersed Boundary Techniques

Authors: 
Shaqfeh, E. S. G., Stanford University
Guido, C., Stanford University
Neo, B. S., Stanford University
Suspended soft particles in viscoelastic fluids are ubiquitous in biological applications and are being utilized with increasing frequency in microfluidic platforms. Biological fluids are often laden with cells which are highly elastic while the suspending fluid usually includes polymeric macromolecules that impart elasticity to the fluid. These fluids can be found everywhere from 3D printing applications to injectable therapeutics. Additionally, it has been recently reported that viscoelastic fluids can enhance microfluidic performance in cell focusing technologies (Raffiee et al. 2017) at low cost further motivating the study of systems of soft particles in viscoelastic fluids. While studies to date have investigated the dynamics of soft solids and membranes in pressure driven flow as well as the shapes and dynamics of soft particles in simple shear flows, little work has been completed to examine the effective rheology of suspensions of these particles. In this talk, we discuss the computer simulation of the arbitrary motion of deformable Neo-Hookean solid particles in simple shear flows and pressure driven flows within viscoelastic fluids. A method similar to the Immersed Finite Element Method (IFEM) presented by Zhang et al. (2007) is utilized to accomplish this task. This method is computationally efficient, allows for good particle number scalability with arbitrary mesh geometries, and also allows the consideration of different fluid constitutive equations to be considered. We first validate our simple shear flow simulations comparing with previous work by Gao et al in 2001 and Villone et al. in 2014. We then discuss the interplay of fluid elasticity and particle elasticity and how this effects the key viscometric functions for shear flows. In this context, we break the viscometric measurables into contributing parts from the fluid (particle induced fluid stress) and the particle (stresslet) thus show interesting trends and underlying physical principles. We find that all components of the particle induced fluid stress are nearly invariant to the deformation (within the parameter range studied), while the shear stress component of the stresslet rapidly decreases in magnitude as elasticity in the fluid increases. Particles in confined channels are also considered and the stresses on the particle are compared for different viscoelastic models. These rheological measures have widespread impact for the design of microfluidic devices and we believe that further investigation of these findings will aid in the design of engineered fluids. The simulation tool also has the capability of allowing the simulation of denser suspensions of particles and more complex geometries opening many new possibilities for future studies of soft matter in viscoelastic fluids.