Anomalous room temperature magnetorheological behavior of colloidal graphene nanogels

Abstract

Weak magnetism is known to exist in graphene systems, yet, as of now, it remains unharnessed for bulk scale applications. Weak ferromagnetic response from chemically exfoliated graphene samples has been employed to harness appreciable magnetorheological effects via the use of novel graphene nanogels. Chemically exfoliated graphene samples have been synthesized and ferromagnetic response has been registered (in tune with scarce reports in literature). Characterizations reveal that presence of magnetic impurities would be unable to yield magnetic moments as obtained and hence the response is innate to the vacancy and defects in the graphenic structure. Polymer based nanogels with infused graphene nanoplatelets has been synthesized and the colloidal gel phase enables harnessing of magnetorheology from such weak moment systems. Strong magnetorheological response is obtained from the colloidal gel phase due to the compact texture which aids in fibrillation of the nanoplatelets. Largely enhanced magnetoviscosity and yield stress have been observed from the gels in similitude to conventional magnetorheological nanocolloids. The presence of dispersed phase with platelet morphology as well as surface lubrication behavior of graphene has been found responsible for certain anomalous behavior such as magnetic shear thickening in the gels which has been explained based on order to disorder transitions under field influence. Transient response of the gels show good modulation caliber in field actuated viscous control as well as minute magnetoviscous hysteresis. The present colloids show novel promise in use of graphene as potential magnetic material in magnetic field governed actuation, control and tuning MEMS/NEMS and allied devices.