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.
