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Scaled particle theory' is applied to a two-dimensional¯uid of hard ellipses. The model predicts a transition from the isotropic alignment of the ellipses to the two-dimensional nematic con® guration in accordance with Monte Carlo simulations. By modifying the molecular shape it is possible to consider an ensemble of hard rectangular particles. The phases observed and the character of the orientational transition turn out to be strongly dependent on details of the particle geometry.

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SUMMARY:We present results o f off-lattice Monte Carlo simulations of weakly charged chains where the charged beads interact with a screened Coulomb potential of Debye-Huckel type. The behaviour of the mean square end-to-end distance and mean-square radius of gyration versus chain length is discussed for various solution conditions characterized by the parameter < = 2AD/b, with A , being the Debye screening length and b the contour distance between neighbouring charged beads. We also evaluate the probability-density distribution for the end-to-end distance R. From the angular correlation function (cosy we estimate the persistence length as well as the chain length dependence of (R') and (Ra). With increasing [it is found to come close to that which is directly obtained from (R ' ( N ) ) and (Ra ( N ) ) . Furthermore, the nonexponential decay of correlations indicates our charged chains to be not wormlike.

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