This paper succeeds in the description of activity (a), chemical potential (μ), and their thermodynamic relations of dispersed and flocculated particles of a one-component colloidal system. The activity of dispersed particles (ad) is expressed by Henry's law and equal to the product of the molar fraction (α) of dispersed particles in a suspension and the activity coefficient (γ0) expressed by Vi/Vmax (Vi : total volume fraction of dispersed and flocculated particles, Vmax : maximum packing density of particles). The activity of flocculated particles (ag) follows Raoult's law and is expressed as (1 − α) using the Gibbs-Duhem equation. The μ value is represented by the defined activity. The difference of μ for the dispersed and flocculated particles (Δμ = μg− μd) was used to evaluate the stability of the colloidal state. The Δμ value was also coupled with the activation energy (ΔGm) for the formation of particle clusters from the dispersed state. The enthalpy term (ΔHm) in the activation energy is equivalent to the maximum value of the interaction energy (Ei(max)) as a function of distance between two particles in the DLVO theory. Based on the above analysis, a colloidal phase diagram for one-component systems of 10-1000 nm diameters was constructed. This phase diagram explains well the experimentally-determined packing density for dispersed and flocculated suspensions.

Keywords: Thermodynamics, Colloidal suspension, Phase diagram, Packing density, Dispersion, Flocculation, Activity, Chemical potential.