Shear thickening effect of a multifunctional magnetorheological gel: the influence of cross-linked bonds and solid particles

Abstract

A multifunctional magnetorheological gel (MMRG) that exhibits both shear thickening (ST) and magnetorheological effects was prepared by dispersing carbonyl iron powder (CIP) into a matrix. In addition to having magnetic-sensitive properties, MMRG can automatically respond to external stimuli due to the presence of B–O cross-linked bonds. The number of cross-linked bonds was changed by varying the mass ratio of pyroboric acid to polydimethylsiloxane (PDMS). The results demonstrated that the relative shear thickening effect (RSTE) and absolute shear thickening effect (ASTE) were both positively correlated with the number of cross-linked bonds. Based on the experimental results, a possible molecular chain model was also proposed and discussed. The influence of excessive solid particles (such as B atoms or CIP) in the matrix on the ST effect was also studied from the point of view of damping. Under the same excitation, the MMRG with low damping led to an increase in the shear rate that can be transmitted to the cross-linked bond and eventually caused a small increase in the RSTE. Additionally, excessive solid particles in the matrix compressed the space available for movement of all the molecular chains, resulting in an increase in the ASTE.