  Magnetic nanocolloids with synthesized super paramagnetic Fe3O4 nanoparticles
(SPION) (5 to 15 nm) dispersed in insitu developed Polyethylene Glycol (PEG
400) and nano silica complex have been synthesized. The PEG nano Silica complex
physically encapsulates the SPIONs, ensuring no phase separation under high
magnetic fields (1.2 T). Exhaustive magnetorheological investigations have been
performed to comprehend the structural behavior and response of the
ferrocolloids. Remarkable stability and reversibility have been observed under
magnetic field for concentrated systems. The results exhibit the impact of
particle concentration, size and encapsulation efficiency on parameters such as
shear viscosity, yield stress, viscoelastic moduli, magnetoviscous hysteresis
etc. Analytical models to reveal the system mechanism and mathematically
predict the magnetoviscosity and magneto yield stress has been theorized. The
mechanistic approach based on near field magnetostatics and Neel Brownian
interactivities can predict the colloidal properties under the effect of field
accurately. The colloid exhibits amplified storage and loss moduli alongside
highly augmented linear viscoelastic region under magnetic stimuli. The
transition of the colloidal state from fluidic phase to soft condensed phase
and its viscoelastic stimuli under the influence of magnetic field has been
explained based on the mathematical analysis. The remarkable stability,
magnetic properties and accurate physical models reveal good promise for the
colloids in transient situations viz. magneto MEMS/ NEMS devices, antiseismic
damping, biomedical invasive treatments etc.
