MELTING OF COLLOIDAL CRYSTALS - A MONTE-CARLO STUDY

Electrostatically stabilized colloidal crystals show phase transitions into liquid and gaslike states as the ionic impurity concentration increases. Using Monte Carlo simulations we theoretically investigate the melting of four colloidal crystals (two fcc crystals and two bcc crystals) which have also been examined experimentally. We calculate the pair correlation function g(r), the total potential energy U(t), and the mean square displacement of a particle <u2> for the colloidal suspensions at various ionic impurity concentrations n(i). We calculate the structure factor S(Q) by Fourier transforming g(r). We find that the parameters g(max) [the maximum of the first peak in g(r)], S(max) [the maximum of the first peak in S(Q)], DELTA-r [the half width at half maximum of the first peak in g(r)], and U(t) (the total potential energy) all show discontinuous behavior on melting. We relate the calculated values of S(max), g(max), and the mean square displacement at the point of melting of our colloidal crystals to that of atomic crystals. We find that the ratio of the rate of change of the Wendt-Abraham parameter, g(min)/g(max) [g(min): the minimum value of g(r) after the first peak], with respect to n(i), in colloidal crystal to that in liquid is constant but specific to the crystal structure (bcc or fcc). We calculate the latent heat of melting of colloidal crystals.