Systems where a phase transition is induced by biquadratic coupling of two different modes, like some types of ferroelectric materials, are analyzed utilizing a Landau-type free energy. The phase diagram associated with this free energy has a critical line that meets a first-order phase boundary...

We study a simple model of DNA divalent cationic surfactant complexation. We find that the combination of electrostatic and hydrophobic effects leads to a cooperative phenomenon in which as the amphiphile is added to the solution containing DNA, a large fraction of the DNA's charge is...

Using molecular dynamics simulations and integral equations wee investigate the structure, the thermodynamics, and the dynamics of a system of particles interacting through a continuous core-softened ramp-like interparticle potential. We found density, dynamic and structural anomalies similar to...

We investigate the thermodynamic properties of a polyelectrolyte solution in the presence of multivalent salts. The polyions are modeled as rigid cylinders with the charge distributed uniformly along the major axis. The solution, besides the polyions, contain monovalent and divalent counterions...

We investigate the relationship between thermodynamic and dynamic properties of an associating lattice-gas (ALG) model. The ALG combines a three-dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom. The competition between the...

The behavior of a neutral polyampholyte, PA, chain with N monomers is analyzed in the framework of Flory's affine network theory of rubber elasticity. The PA chain, in addition to the neutral monomers, also contains an equal number of positively and negatively charged monomers. In order to...

We study the interactions between two negatively charged macroscopic surfaces confining positive counterions. A density-functional approach is introduced which, besides the usual mean-field interactions, takes into account the correlations in the positions of counterions. The excess free energy...

We investigate the relation between thermodynamic and dynamic properties of an associating lattice gas (ALG) model. The ALG combines a two-dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom. From the competition between the...

We formulate an extension of the Debye–Hückel–Bjerrum theory [M.E. Fisher, Y. Levin, Phys. Rev. Lett. 71 (1993) 3826] to the fluid state of a highly asymmetric charged colloid. Allowing for the formation of clusters consisting of one polyion and n condensed counterions, the total Helmholtz...

We present a model for describing flexible polyelectrolytes in a good solvent and in the presence of monovalent salt. The molecule composed by N monomers is characterized by the end-to-end distance Re=b(Z-1)γ and the number of associated counterions n. At high temperatures the polyelectrolyte...