Effect of different molecular coatings on the heating properties of maghemite nanoparticles

In this work, the effect of different molecular coatings on the alternate magnetic field-induced heating properties of 15 nm maghemite nanoparticles (NPs) in water dispersions was studied at different frequencies (159-782 kHz) and field amplitudes (100-400 G). The original hydrophobic oleate coating was replaced with dimercaptosuccinic acid (DMSA) or polyethylene glycol trimethoxysilane (PEGTMS), while cetrimonium bromide (CTAB) or stearic acid-Polaxamer 188 (SA-P188) were intercalated or encapsulated, respectively, to transfer the dispersions into water. Surface modification, based on intercalation processes, induced clustering phenomena with the formation of spherical-like assemblies (CTAB and SA-P188), while ligand-exchange strategies kept the particle isolated. The clustering phenomenon has detrimental effects on the heating performances compared with isolated systems, in line with the reduction of the Brown relaxation times. Furthermore, broader comprehension of the heating phenomenon in this dynamic system is obtained by following the evolution of the SPA and ILP with time and temperature beyond the initial stage.