Do you subconsciously dread the first drop of ketchup out of its bottle? Have you noticed the inconsistent flow in the substance as you try to coax the ketchup out, only to have a huge gush of flow when you realize you have coaxed it a little too well?
You are not alone! While this may be a minor inconvenience to most, this is a prime example of what researchers call, "soft solid." A soft solid refers to materials that are not quite liquid and not quite solid, it is what many researchers refer to as complex fluid.
In this article written by Kacey Deamer of LiveScience.com, Kacey gives advice on how to optimize your ketchup experience.
Shake the ketchup bottle to ensure a thorough mixture or smooth flow
Maneuver the bottle to ensure ketchup flow to the lid
Tilt and pour, make sure you apply just the right amount of force. Kacey notes that a full bottle is much more easy to flow as the sauces pushes down until the bottle is tilted. With a bottle that is almost empty, more force is required.
While you may not be quite concerned on getting your ketchup right, you may be more focused on getting your sample right. Just as Kacey points out the importance of applying the right amount of force, when dealing with the viscosity of your sample, accessing true viscosity at various shear rates can be a benefit to understanding your sample behavior.
Complex fluids like ketchup, paints, blood, and much more require viscosity measurements at various shear rates to truly see shear thinning or shear thickening behavior. This is what we refer to as a non-Newtonian fluid (Learn about Newtonian v. non-Newtonian fluids). It may not always be the case that your sample viscosity stays the same at different applied forces. Like ketchup, applying too little force will cause the ketchup to flow much less than applying too much force which will result in a splatter of ketchup. How is this important you ask?
Perhaps this would not be the focus of a customer sitting in a diner eating their french fries drenched in ketchup, however, a developer of drug injections may differ. When it comes to protein therapeutics, self-injection formulations are of high demand and importance to many patients who deal with all types of health related conditions.
As these drugs are being injected into live patients who depend on these products as a matter of life or death, it is important for R&D scientists to be able to mimc the drug injection behavior by measuring the viscosity of their drugs at specific shear rates that optimize the delivery of the drugs.