Role of polymeric surfactants on the growth of manganese ferrite nanoparticles

Abstract

The growth kinetics of manganese ferrite (MnFe2O4) nanoparticles was studied by solvothermal reaction of iron and manganese salts in ethylene glycol as a solvent. To explore the mechanism of the nanoparticle formation and development, polyethylene glycol (PEG) with different molecular weights and polyvinyl pyrrolidone (PVP) were used as polymeric surfactants to investigate their effects on the formation of MnFe2O4 nanoparticles. The size evolution and the size distribution not only dependent on the kind of surfactant but also on the time and temperature of reaction process. In the presence of low molecular weight PEG (PEG300), nanoparticles with diameter of 180nm and narrow size distribution could be produced at 160°C during 12h of reaction while the nanoparticles with average size of 330nm were formed by using PEG300 at 200°C and 48h. Therefore, by increasing the temperature and the time of reaction, the size of nanoparticles was increased and finally reached a critical size and then collapsed. When a large molecular weight surfactant PEG10000 was used, the nanoparticles with average size of 230nm were formed at 180°C and 60h. In the case of PEG300 and PEG10000 as lower and higher molecular weights, the separation between building blocks occurred after 60h and 48h for 180°C and 200°C, respectively. However, more collapses between primary building blocks were observed by using PEG10000. The nanoparticles were composed of small building blocks and exhibited a spherical mesocrystal structure which was demonstrated from the TEM and scanning electron microscope (SEM) results. The investigation on the growth mechanism of the nanoparticles indicated that the formation of manganese ferrite was followed by the attachment and growth of primary building blocks and their Ostwald ripening process.