Interfacial free energy of a hard-sphere fluid in contact with curved hard surfaces

Abstract

Using molecular-dynamics simulation, we have calculated the interfacial free energy, \gamma, between a hard-sphere fluid and hard spherical and cylindrical colloidal particles, as functions of the particle radius R and the fluid packing fraction \eta= \rho\sigma^3/6, where \rho and \sigma are the number density and hard-sphere diameter, respectively. These results verify that Hadwiger's theorem from integral geometry, which predicts that \gamma for a fluid at a surface, with certain restrictions, should be a linear combination of the average mean and Gaussian surface curvatures, is valid within the precision of the calculation for spherical and cylindrical surfaces up to \eta about 0.42. In addition, earlier results for \gamma for this system [Bryk, et al., Phys. Rev. E, 68, 031602 (2003)] using a geometrically-based classical Density Functional Theory are in excellent agreement with the current simulation results for packing fractions in the range where Hadwiger's theorem is valid. However, above \eta about 0.42, \gamma(R) shows significant deviations from the Hadwiger form indicating limitations to its use for high-density hard-sphere fluids. Using the results of this study together with Hadwiger's theorem allows one, in principle, to determine $\gamma$ for any sufficiently smooth surface immersed in a hard-sphere fluid.