Probing temperature-sensitive behavior of pNIPAAm-coated iron oxide nanoparticles using frequency-dependent magnetic measurements

Ferromagnetic iron oxide nanoparticles of about 33 nm in diameter were synthesized by high-temperature decomposition of an iron–oleate complex, using octadecene as the solvent. These particles were subsequently coated with polyN-isopropylacrylamide (pNIPAAm) by a surfactant exchange method. Temperature-sensitive behavior of these particles was studied using ac susceptibility and dynamic light scattering (DLS) measurements. Shifts in the imaginary part of the ac susceptibility are correlated with swelling and collapse of pNIPAAm as a function of temperature.