Ionic liquid-based shear thickening fluid: Cushioning performances of direct impact

Ionic liquids (ILs) have multifunctional properties including ultra-wide temperature and pressure tolerance, making them an ideal candidate for use as shear-thickening fluids (STFs) for impact protection. However, the direct impact behaviors of IL-based shear thickening fluids (ILSTFs) have not been thoroughly explored, yet critical in real applications, not to mention as a discontinuous shear thickening colloidal dispersion. This study systematically investigates the direct impact behavior of ILSTFs, focusing on impulse duration and peak force to evaluate cushioning performance. The results show remarkable non-Newtonian behavior, with a peak viscosity of 444 Pa & sdot;s and energy absorption efficiency exceeding 97 % for impacts above 5 m/s. Two unique cushioning characteristics are firstly witnessed in the non-Newtonian dispersions versus Newtonian system in impact cushioning, namely early impact response initiation and high force plateau before peak. This makes ILSTFs suitable for impact cushioning. For shallow depth impacts, a floating film can enlarge the loading zone and drive it radially outwards, further enhancing cushioning performance when enveloping the ILSTF in flexible solids. A transition from merely added mass to solidification in the ILSTF pool during impact is observed as a peak force jump. It is characterized by an MPa-level compression stress. It occurs of impactor beyond a specific velocity threshold. The depth and the impact velocity dependence of the impact peak force are quantitively presented, with a linear fitted peak force-velocity relationship. The current impact setup identifies a critical cushioning depth of 8.83 mm, pivotal for its actual cushioning application.