Stick or Splash? Thixotropy decides

We use high-speed imaging to study droplet impacts of thixotropic non-Newtonian fluids on pre-coated horizontal surfaces to explore the effect of thixotropic aging and rejuvenation on impact behavior, an aspect missing from the literature on this subject. Our results show that thixotropic aging has a significant effect on the stick-or-splash dynamics of yield-stress fluids: aged samples are more likely to stick. We test existing dimensionless groups with fluids of different microstructure (Carbopol and Laponite) and various degrees of thixotropic aging properties. Characterizing flow properties of aged samples is challenging since any deformation inherently rejuvenates and breaks down the microstructure and rheological properties. Steady state properties are therefore undefined for aged samples, and we propose alternative methods for characterizing aged rheological properties and using these in dimensionless groups that rationalize the stick-or-splash regime maps.