In Situ Observation of Domain Structure in Monolayers of Arachidic Acid/γ-Fe₂O₃ Nanoparticle Complexes at the Air/Water Interface

Abstract

The Langmuir layer behavior of arachidic acid/γ-Fe 2 O 3 nanoparticle complexes was studied at the air/water interface. The subphase was an aqueous colloidal solution (hydrosol) of γ-Fe 2 O 3 nanoparticles with an average diameter of 8.3 nm and with a standard deviation of ±1.4 nm. Formation of the complex between arachidic acid and γ-Fe 2 O 3 nanoparticles was studied with surface pressure−area isotherms, surface potential−area isotherms and Brewster angle microscopy. Increasing surface pressure resulted in a transition from well-separated domains of the complex to well-compressed, nanoparticulate layers and, ultimately, to multiparticulate layers. The magnetic nanoparticles and layers of nanoparticles on solid substrates were studied with FTIR, Mössbauer spectroscopy and vibrating sample magnetometry (VSM). The γ-Fe 2 O 3 nanoparticles and Langmuir−Blodgett films with the nanoparticles showed superparamagnetic properties. The stability of the γ-Fe 2 O 3 nanoparticle hydrosol solution was studied by ζ potential measurements. Positively charged γ-Fe 2 O 3 nanoparticles in aqueous hydrosol solution at pH 3.5−5 showed excellent long-term colloidal stability.