Particle-medium interaction induced disability of shear thickening characterized by solid-state 1H low-field NMR spectroscopy

Mediums and particles could form a typical shear thickening fluid (STF) whose viscosity increased significantly while shear rate was larger than the critical value. Such jump of viscosity could be controlled by particle-medium interactions. The quantitative relationship between particles and different mediums was still less studied. We used polyethylene glycol 200 and silica nanospheres as a typical STF. The bridging effect may cause a gel while bad medium, like water, made STF dysfunctional. The relaxation behavior and the dynamical heterogeneity of these samples were characterized by solid-state 1 H low-field NMR. One mediate apparent spin-spin relaxation time ( T 2 ) could be found by fitting fully refocused FID in the typical STF. A strong interaction with typical T 2 of 0.14 ms was extracted in particle gels with bridging effect. Interestingly, when two good mediums were mixed, STF became gel-like and their T 2 decreased more rapidly than single medium with increasing particle content. On the contrary, bad medium preferentially lubricated particle surface and broke original particle-medium interactions, which was evidenced by a higher T 2 value when small amount of bad medium was added. Such dynamic information obtained from NMR agreed well with the corresponding rheology behavior. A tentatively quantitative criterion of dynamics was proposed to judge whether shear thickening can occur in a particle suspension.