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Electronic Dispensing and Extensional Viscosity

February 1, 2022

Most fluids are non-Newtonian, which means that their viscosity is dependent on shear rate or the deformation history. Non-Newtonian fluids display either a non-linear relation between shear stress and shear rate, have a yield stress, or viscosity that is dependent on time or deformation history.NewtoninaVsNonNewtonianViscosityViscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Rheological behaviors, such as viscoelasticity, effects many industrial applications, including spraying and atomization, food processing, coating, inkjet printing,  and industrial dispensing. 

Extensional viscosity is defined as the resistance of a fluid to flow through a field involving a change in cross-sectional area. Extensional deformation and extensional shearing have a significant impact on industrial processes, such as dispensing. Because extensional flows greatly impact the behavior of polymer molecules and asymmetric particles, understanding extensional viscosity allows you to improve your industrial processes. 

Extensional Viscosity (Blood)

In dispensing, non-Newtonian fluid bridge break up is resisted by extensional viscosity and high shear viscosity that leads to problems like delayed break up, satellite drop formation and stringiness. (Hammad Faizi, Northwestern University) These challengers are common when it comes to dispensing in the electronic industry, specifically electronic packaging. Because of the viscoelastic bridges produced during the electronic packaging dispensing process, a speed vs. precision trade off challenge is presented. Measuring the extensional properties of your dispensed substance will allow you to optimize your dispensing processes. 

viscoelastic bridges in electronic dispensing

The VROC® initium one plus is the leading automatic, high throughput viscometer. The VROC initium one plus includes an intuitive software that allows automatic testing, which allows you to "set and forget" your viscosity measurements. You are now able to run extensional viscosity measurements on the VROC initium one plus automated viscometer! This greatly increases efficiency and saves expert and professional labor for your most valuable work instead of setting up and running sample testing.

initium one plus flow rate vs sample size-2Want to learn more about the VROC initium one plus, or specifically how you can automate your extensional viscosity measurements with this viscometer? Contact us today to speak with one of our rheology experts! Talk to a SpecialistAt the 2022 Virtual Viscosity Summit, Hammad Faizi - PhD Candidate in Mechanical Engineering, Northwestern University - explored how torsion may destabilize viscoelastic liquid bridges and decrease the time to pinch off. Showing that viscoelastic bridges which would never break under the action of gravity and capillarity alone but can be broken in O (1 s) due to the edge fracture process. Download the entire presentation to learn more about Fracture of Viscoelastic bridges for dispensing applications.

Northwestern  2022 Virtual Viscosity Summit YouTube (1)

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