INVESTIGATIONS INTO THERMODYNAMIC PROPERTIES OF COLLOIDAL-SPHERE SUSPENSIONS

Fadi .S. JARDALI

     (i) The effects of varying the repulsive exponent 'n' on the osmotic equilibria of 3‑dimensional monodisperse colloidal‑sphere (NVT) systems have been investigated by Monte Carlo simulations. The order/disorder (solid/ fluid) transition regions have been located. The model effective pair potential is of the colloidal soft‑sphere form:

    Where ε is the unit energy, r is the separation between particle centers, is the particle diameter, and n is the repulsive exponent.

      (ii) The effects of varying the degree of polydispersity (10%, 20%, & 30%) on the equation of state at different values of 'n' (6, 9, & 12) have been also investigated by computer simulation for a 3‑dimensional (NVT) system. The colloidal‑sphere potential has again been used for these simulations, replacing the value of the core particle diameter (σ) by the arithmetic mean of the interacting particle diameters, i.e. (σ _i + σ _j )/2. The order / disorder transition regions have been subsequently located at the three values on ‘n’.

    (iii) Variable polydisperse (canonical) systems have been also investigated. The effects of varying a so‑called 'surface energy term ', on the size distribution have been studied by computer simulations. This term was added as an extra energy term to the effective pair potential. Results are reported on constant packing fraction (NVTY) systems, and constant total area (NVTA) systems.

    (iv) Spherical particles were prepared by polymerization of the styrene monomer, using dispersion polymerization techniques. The colloidal spheres were sterically stabilized, resulting in samples of ~10% polydispersity ( σ = 800 nm ). Experimental osmotic pressure measurements on these colloidal suspensions, at packing fractions ranging from 0.12 to 0.52, have been made. A conventional (modern) colloid osmometer was used and subsequent comparison with the quasi‑experimental computer‑data is.also, reported.