Viscosity is one of the major properties an engineer should consider while comparing specialty adhesives. Depending on the application and the desired assembly process, choosing the correct adhesive viscoisty may be critical. We organized this blog post to explain some of the fundementals of viscosity, and explain what we consider to be low, medium and high viscosity values.
Viscosity vs. Thixotropy
We use the terms viscosity and thixotropy a lot around the site so I think we should first explain the differences between these two properties.
Viscosity is a property that can be measured for every fluid and represents how the material resists deformation by shear or tensile stress. Basically viscosity determines how hard it is to mix a material. Higher the viscosity, the harder ther material is to mix.
Thixotropy is a property that is only used to describe materials that exhibit a stable form at rest but become fluid when agitated. Basically a thixotropic fluid changes viscosity according to the level of stress applied.
Some materials may be difficult to mix (high viscosity), but will remain fluid even without agitation (non-thixotropic). Other materials may be easy to mix (low viscosity), but will not readily flow without outside intervention (thixotropic).
Side Note: Technically, thixotropic fluids are non-newtonian. Simply put, newtonian fluids will not change viscosity according to the stress applied, non-newtonian fluids will. Thixotropic fluids are one type of non-newtonian fluids, however other types exist.
Some common viscosity examples
Just to help you understand viscosity a little bit more we've collected a short list of example material and their approximate viscosities. Viscosity is commonly measured in centipoise (cps).
Castor oil: 1,000cps
Caulking compound: 75,000cps
Peanut butter: 250,000cps
Viscosity of adhesives
For the purposes of simplification, on our site we may refer to polymer adhesives as low, medium and high viscosity materials. As a general rule: