The issue of whether extensional viscosity is a concept that causes more confusion than enlightenment is addressed. This author’s view is that misuse of the concept certainly has caused much confusion and, although it is in principle a simple and straightforward idea, it continues to be misused. What is straightforward is the formal definition of extensional viscosity, for steady uniform extens...

Droplets of de-ionized water and four aqueous surfactant solutions were generated in oil using a microfluidic flow-focusing device. The morphological developments of the drops in extensional flow and confinement-induced shear flow at various extension rates were studied using a hyperbolic contraction. This novel approach to droplet deformation within a microfluidic device allowed the probing of...

In the discipline of non-Newtonian materials, the ability to control viscoelastic stresses is very desirable in ascertaining important properties of the influenced materials. We apply the nonlinear geometric control theory to examine the controllability of various popular constitutive models with imposed homogeneous extensional flow. The subsequent constitutive laws considered here include the ...

A novel noncontact technique based on hydrodynamic trapping is presented to study the dissolution of freely suspended liquid microdroplets into a second immiscible phase in a simple extensional creeping flow. Benzyl benzoate (BB) and n-decanol microdroplets are individually trapped at the stagnation point of a planar extensional flow, and dissolution of single microdroplets into an aqueous solu...

Complex fluids containing long polymer chains exhibit measurably large resistance to stretching or extensional flows, due to additional stresses generated by the extensional deformation of the underlying fluid microstructure. Understanding and quantifying the response of such elastic fluids to extensional flows is necessary for optimizing fluid composition for technological applications like in...