Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Poster: Colloids and Complex Liquids

CPP 16.45: Poster

Tuesday, March 27, 2012, 18:15–20:45, Poster A

Fundamental measure density functional for the soft sphere erf-model — •Markus Burgis and Matthias Schmidt — Theoretische Physik II, Physikalisches Institut, Universitaet Bayreuth, D-95440 Bayreuth

As a generic model for soft colloids we consider a fluid of repulsive particles where the Mayer bond is a superposition of two error functions, which allows to interpolate between hard spheres and Gaussian cores. The corresponding pair interaction potential contains the colloidal size and the length scale over which the soft repulsion decays. We deconvolve the Mayer bond for general mixtures of such particles into single particle weight functions. Both the soft sphere weight functions and the Kierlik-Rosinberg scalar hard sphere weight functions follow from a set of coupled partial differential equations, where first derivatives with respect to the geometric model parameters are related to (multiple) application of the Laplace operator in position space. Rescaling the length scales in the weight functions allows to construct an accurate star approximation to the exact triangle diagram in the virial series. Corresponding scaling and exploiting isometric transformations of the weight functions leads to a fundamental measure free energy density functional for the pure fluid. Considering cases where the particle core is effectively impenetrable, we calculate the bulk fluid radial distribution function via the Ornstein-Zernike route. Comparison to results from our Monte Carlo simulations demonstrates over a broad range of densities that the theory accurately reproduces the loss of liquid structure upon increasing softness of the repulsion.