THIXOTROPY

Breaking and Rebuilding...Maybe

Thixotropy investigations are very helpful to provide insight into the effects of product manufacturing processes, handling, and dispensing.  In this assay, the sample is subjected to several shear rate steps to model situations that typically cause thinning. The extent and rate of rebuilding, or lack thereof, is then determined. Depending on the product purpose, the desired extent and rebuild time after shear thinning will range between immediate and never.  This test can also be used to model manufacturing processes such as on-off pumping materials through pipes or dispensing from tubes.  In particular for topical products, understanding thixotropic properties are important during application onto and penetration through skin that may affect efficacy.

Figure 1 compares two creams after being subjected to a brief increased shear (Step 2) exhibiting different rebuild curves (Step 3) that may effect product properties and performance.  

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2 compares 2  brands of a classic thixotropic product - ketchup.  STEP 1 (baseline) models storage in the bottle at low shear rate, STEP 2 (shear-thinning) models dispensing at higher shear and STEP 3 (rebuilding) at low shear rate typically same as STEP 1 to show the different extent and rate of rheological rebuilding compared to STEP 1 viscosities.  Toothpaste and paint are also designed to have highly controlled thixotropic properties.