Eur. Phys. J. E 6, 29-35 (2001)
Nanoparticles superficial density of charge in electric double-layered magnetic fluid: A conductimetric and potentiometric approach
A.F.C. Campos1, F.A. Tourinho1, G.J. da Silva2, M.C.F.L. Lara2 and J. Depeyrot21 Complex Fluids Group, Instituto de Química, Universidade de Brasília, Caixa Postal 04478, 70919-970, Brasília (DF), Brazil
2 Complex Fluids Group, Instituto de Física, Universidade de Brasília, Caixa Postal 04455, 70919-970, Brasília (DF), Brazil
tourinho@fis.unb.br
(Received 9 May 2001 and Received in final form 17 July 2001)
Abstract
We analyze potentiometric and conductimetric measurements
simultaneously performed on Electric Double-Layer Magnetic Fluid based on
cobalt ferrite nanoparticles, in order to obtain the pH-dependence of the
particle surface charge density. We propose a mechanism for the charging of
the particle surface. This model considers the ferrofluid solution as a
mixture of strong and weak diprotic acids. We show how an exact
analytical treatment involving proton transfer between the particle surface
and the bulk solution allows the construction of a speciation diagram of the
charged superficial sites. The saturation value of the superficial density
of charge is found to be equal to 0.326 
0.065 C m-2.
75.50.Mm - Magnetic liquids.
82.70.Dd - Colloids.
82.60.Hc - Chemical equilibria and equilibrium constants.
82.80.Fk - Electrochemical methods.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
