# Drop impact experiments of non-Newtonian liquids on micro-structured surfaces

## TL;DR

This study investigates the impact dynamics of shear-thickening and shear-thinning non-Newtonian liquids on micro-structured surfaces, revealing different spreading behaviors and scaling laws compared to Newtonian liquids and prior findings.

## Contribution

It provides new experimental insights into how non-Newtonian liquids behave upon impact on micro-patterned surfaces, especially on superhydrophobic surfaces, extending previous work on Newtonian and yield-stress fluids.

## Key findings

- Shear-thickening liquids like cornstarch follow Newtonian scaling laws at low concentrations.
- Visco-elastic liquids like Carbopol behave as predicted on hydrophilic surfaces.
- Different scaling laws are observed for Carbopol on superhydrophobic surfaces.

## Abstract

The spreading dynamics of Newtonian liquids have been extensively studied in hydrophilic and hydrophobic surfaces and its behavior has been extensively explored over the last years. However, drop impact of Non-Newtonian liquids still needs further study. Luu and Forterre (J. Fluid Mech., 632, 2009) successfully found scaling laws for yield-stress fluids on hydrophilic surfaces. They also uncovered interesting and yet unexplained regimes when the impact was performed on a superhydrophobic surface. In this work, we perform drop impact experiments on micro-patterned surfaces with two types of non-Newtonian liquids: one showing shear-thickening behavior and another one showing shear-thinning. Our results show that a typical shear-thickening liquid as cornstarch -at least a the relatively low concentration of 30\%w/w- spreads according to the scaling laws of Newtonian liquids, whereas visco-elastic liquids as Carbopol behave as predicted by Luu and Forterre for impact on hydrophilic surfaces, but show different scaling laws when they impact on superhydrophobic surfaces.