Microscopic theory of solvent mediated long range forces : influence of wetting

نویسندگان

  • A. J. Archer
  • R. Evans
  • R. Roth
چکیده

PACS. 61.20Gy – Theory and models of liquid structure. PACS. 82.70Dd – Colloids. Abstract. – We show that a general density functional approach for calculating the force between two big particles immersed in a solvent of smaller ones can describe systems that exhibit fluid-fluid phase separation: the theory captures effects of strong adsorption (wetting) and of critical fluctuations in the solvent. We illustrate the approach for the Gaussian core model, a simple model of a polymer mixture in solution and find extremely attractive, long ranged solvent mediated potentials between the big particles for state points lying close to the binodal, on the side where the solvent is poor in the species which is favoured by the big particles. Determining the effective force between two (big) particles immersed in a solvent constitutes a canonical problem in condensed matter science. From the statistical mechanics viewpoint one should integrate out the relevant degrees of freedom of the solvent particles in order to obtain the the effective pair potential [1]. In the case of colloidal systems, where the colloidal component is very much larger than the particles constituting the solvent, the description of the complex, multi-component system in terms of an effective colloid-colloid potential forms a cornerstone of the subject. Well-known examples are the DLVO potential for charge stabilized systems and the hard-sphere potential for sterically stabilized systems [2]. The effective potential between colloids exhibits new features if particles of intermediate size, such as non-adsorbing polymer or small colloids, are added to the solvent. When two big colloids (b) are sufficiently close that the intermediate sized particles are depleted from the region between the big colloids the effective bb potential, V ef f bb (r), can exhibit entropically driven attraction. Within the Asakura-Oosawa (AO) model [3], where the colloids are hard spheres and the polymer is treated as ideal (inter-penetrating and non-interacting) the resulting depletion potential is purely attractive and its finite range is equal to the 'diameter' of the polymer coil. For mixtures of hard-sphere like colloids the effective potential between the bigger colloids exhibits both attraction and repulsion; short ranged correlations arising from the packing of the smaller colloids gives rise to an exponentially damped, oscillatory effective potential whose decay length is simply the bulk correlation length [4], in keeping with the c EDP Sciences

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Crossover from first-order to critical wetting in methanol on alkanes*

A mean-field theory is presented which describes the basic observations of recent experiments revealing rich wetting behaviour of n-alkane/methanol mixtures at the liquid–vapour interface. The theory is based on a microscopic lattice-gas model from which a Cahn–Landau phenomenological approach is derived. Besides the physics associated with the short-range components of the intermolecular inter...

متن کامل

Solvent mediated interactions close to fluid-fluid phase separation: microscopic treatment of bridging in a soft-core fluid.

Using density functional theory we calculate the density profiles of a binary solvent adsorbed around a pair of big solute particles. All species interact via repulsive Gaussian potentials. The solvent exhibits fluid-fluid phase separation, and for thermodynamic states near to coexistence the big particles can be surrounded by a thick adsorbed "wetting" film of the coexisting solvent phase. On ...

متن کامل

Cross-over between first-order and critical wetting at the liquid-vapour interface of n-alkane/methanol mixtures: tricritical wetting and critical prewetting

A mean-field theory is presented which describes the basic observations of recent experiments revealing rich wetting behaviour of n-alkane/methanol mixtures at the liquid-vapour interface. The theory is based on a microscopic lattice-gas model from which a Cahn-Landau approach is derived. Besides the physics associated with the short-range components of the intermolecular interactions, the effe...

متن کامل

Thermal fluctuation forces and wetting layers in colloid-polymer mixtures: derivation of an interface potential.

We discuss wetting layers in phase-separated colloid-polymer mixtures adsorbed at a vertical wall, observed in recent laser scanning confocal microscopy experiments. Matching of colloid and solvent dielectric properties renders van der Waals forces negligible and provides a system governed by short-range forces and thermal fluctuations on which the subtle predictions of renormalization group (R...

متن کامل

Complete wetting near an edge of a rectangular-shaped substrate.

We consider fluid adsorption near a rectangular edge of a solid substrate that interacts with the fluid atoms via long range (dispersion) forces. The curved geometry of the liquid-vapour interface dictates that the local height of the interface above the edge ℓ(E) must remain finite at any subcritical temperature, even when a macroscopically thick film is formed far from the edge. Using an inte...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2002