ABSTRACT
It should be realized that every single detached molecule or particle, immersed in a liquid medium, is endowed with a Brownian (BR) free energy of 1½ kT (Einstein, 1907), where k is Boltzmann’s constant (= 1.3806 × 10-23J/K) and T the absolute temperature in degrees K. This energy keeps it in solution or in suspension, provided the energy of attraction between similar molecules (or particles) immersed in that liquid is less than 1½kT per pair of molecules or particles. But while a very small molecule has a Brownian free energy of +1½kT, a large particle also has a Brownian free energy of only +1½kT. Thus, micron-sized particles, each pair of which would typically have a contactable surface area (Sc) of the order of 104 nm2, will overcome the repulsive forces of Brownian motion and become destabilized even if their free energy of mutual attraction, in a given liquid at close range, is as small as –10-3 mJ/m2. Whilst the energies of thermal motion, or diffusion, are relatively small, they are not always negligible; in apolar media they can be the major contribution to solubility or stability. As all single entities immersed in a liquid are endowed with +1½kT, this contribution clearly plays the greatest role in the case of the smallest molecules or particles, as these have the smallest surfaces of mutual contact.
