A Thermodynamic Theory of Suspension I. Thermodynamic Theory
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Abstract
The stability of a colloid has been treated in terms of repulsion by electric charge and attraction by cohesion of particles, but colloid particles are v-times larger in volume-size than the solvent molecules. v is as large as 103-6 and the molar energy of cohesion H/v is negligibly small compared with the electric repulsion energy Wel/v. Cohesion acts over the distance of 1—5 A or only at the contact point. H does not increase with v, contrary to the DLVO theory. The molar energy of sedimentation Wsed/v is taken as an influential factor for the stability of a colloid of large particles. It is calculated from Stokes law as Wsed/v = Δρ u2, where Δρ is the density difference and u is the stationary velocity of sedimentation equal to (Δρ/η)(2/9)gr2, where η, r, and g are viscosity of solvent, radius of particle, and acceleration constant of gravity, respectively. Sedimentation occurs when Wsed/v is equal to kT/3, i.e., the perpendicular component of the energy of Brownian motion. The critical radius rc is rc...