Chain Formation of PNIPAM-Coated Magnetic Nanoparticles in an External Magnetic Field and the Effect of Temperature

In this study, we demonstrate that the length and distribution of the aggregates were dependent on the temperature of the aqueous solution of poly(
$N$
-isopropylacrylamide) (PNIPAM). Magnetic resonance relaxometry, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to observe the chaining of magnetic polymer nanoparticles (NPs) on a micrometer scale under a
$0.3T$
magnetic field. As the temperature increased, the magnetic interparticle interactions increased, therefore increasing the chain formation. By utilizing the temperature-mediated lower critical solution temperature (LCST) of PNIPAM from hydrophilic to hydrophobic at 45 °C, multiple-thick-chain-like structures can be obtained.