## "Mesoscopic theory of phase transitions in colloidal systems"

### prof. Alina Ciach, Instytut Chemii Fizycznej PAN

¶roda, 12 pa¼dziernika 2005

A mesoscopic theory for the primitive model of ionic systems is developed for arbitrary size, $\lambda=\sigma_+/\sigma_-$, and charge, $Z=e_+/|e_-|$, asymmetry. The phase diagram and correlation functions are obtained in the asymptotic regime $\lambda\to\infty$ and $Z\to\infty$, and for infinite dilution of the larger ions (volume fraction $n_p\sim 1/Z$ or less), in a mean-field approximation. We find a coexistence between a very dilute 'gas' phase and a crystalline phase in which the macroions form a bcc structure with the lattice constant $\approx 3.6\sigma_+$. Such coexistence was observed experimentally in deionized aqueous solutions of highly charged colloidal particles.