Overview of the phase diagram of ionic magnetic colloidal dispersions

We study ionic magnetic colloidal dispersions, which are constituted of gam ma -Fe2O3 nanoparticles dispersed in water, and stabilized with electrostat ic interparticle repulsion. The phase diagram fIV versus Phi (Pi: osmotic p ressure, V: particle volume, Phi: particle volume fraction) is explored, es pecially in the range of high Pi and high Phi. The osmotic pressure Pi of t he colloidal dispersion is known either by a measurement either because it is imposed during the sample preparation by osmotic compression. The struct ure of the colloidal dispersion is determined from Small Angle Neutron Scat tering (SANS). Two regimes can be distinguished. At high pressure, fluid an d solid phases can exist. Their structure is governed by strong electrostat ic repulsion, the range of which is here evaluated. At low pressure, gas, l iquid and glassy solids can exist. Their structure results from a sticky ha rd sphere potential.