What Is Viscoelasticity?

Viscoelasticity is best understood in the context of elasticity and viscosity.

Elasticity applies to solid materials. Elastic substances “bounce back” to their original state when a force is removed from them (e.g. rubber). Viscosity applies to liquids.  Viscosity describes how readily a fluid flows. The more viscous a liquid is, the thicker it is and the slower it flows (e.g. maple syrup). Viscoelasticity is a combination of both elasticity and viscosity. A viscoelastic material exhibits both properties, tendency to return to original form and to resist flow (e.g. mercury at room temperature).

This video shows the break-up of a liquid jet into droplets. Note the range of droplet sizes formed. This is the behavior of a Newtonian fluid. A Newtonian fluid is a fluid in which the viscous stresses arising from its flow, at every point, are linearly proportional to the local strain rate—the rate of change of its deformation over time.

In other words, if you punch it, your fist goes right through...like water. A non-Newtonian fluid is different. When you punch it, your fist bounces off of it as would off of a hard surface.  HMWPIB renders liquids non-Newtonian but only for the instant of shear/stress. Otherwise it behaves like a Newtonian fluid. 

This high-speed video shows the 'gobbling drop' effect caused by traces of a dissolved polymer (100 ppm high molecular weight polyacrylamide) in water. Increased surface tension drives the end drop to 'climb' up the jet against gravity and to 'gobble' smaller drops forming on the jet.

At a concentration of 5 ppm HMWPIB limits this viscoelastic effect to the split second during which sheer forces are encountered as fluid passes through a spray nozzle. Before and after sheering, the liquid behaves as a Newtonian fluid. Our testing has demonstrated near elimination of superfine droplets in the resulting air-fluid mixture (98%).