Calculation of the pair potential interaction in electric double-layered magnetic fluids: a quantitative analysis of the pH-dependent phase diagram

Abstract In this work, the phase behavior of an acidic EDL-MF sample based on cobalt ferrite nanoparticles is studied in absence of external magnetic field and constant temperature. An experimental pH-dependent phase diagram of the ferrofluid sample is established and the result shows three phases in different pH ranges: a sol phase in low pH conditions, a gel phase when 3.8 pH 5.2 and a coagulated phase up to pH 5.2 in acidic medium. The pH-dependence of the nanoparticle surface charge density is taken into account in the framework of the extended DLVO pair potential theory allowing a quantitative analysis of the observed phase diagram.