We analyze potentiometric and conductimetric measurements, simultaneously performed in several complex systems (Brönsted acid-base-type). The results show an excellent agreement between reported and obtained values of the dissociation constants of the involved equilibria. A similar analysis is proposed to account, in electric double layered magnetic fluids (EDL-MF), for the charging of the particle surface based on a proton transfer proccess at the interface with the bulk dispersion. This model allows to relate the pH dependence of the phase diagram to the variations of the nanoparticle surface charge density, which leads to a useful method to monitor the colloidal stability of EDL-MF.

Magnetic birefringence measurements are performed under a static field on Electric Double Layered Magnetic Fluids based on copper and zinc ferrite nanostructures. The optical birefringence is related to a single-particle effect and well described by a Langevin model which includes a log- normal distribution of particles. By the field-induced birefringence level, these new magnetic fluids are comparable to usual ones, a result which could offer a new way for biological applications.