EFFECT OF HYDROSTATIC-PRESSURE ON THE INTERACTION OF PARTICLES AND THE STABILITY OF SUSPENSIONS

The molecular structure of a liquid or gaseous medium prevents it from penetrating small gaps (less than the molecular diameter of the medium) between solid surfaces. Consequently, there is a void around the point of contact even in a wetting liquid. An increase in the volume of the system on formation of a contact weakens the adhesion, but the unsymmetrical action of hydrostatic pressure, P, on particles squeezes them together and strengthens adhesion. The overall effect of pressure on the force and energy of adhesion reflects the competition of these factors and is determined by the shape of the contacting surfaces. The contribution of pressure can prove substantial compared to the molecular forces of cohesion in lyophobic systems at P almost-equal-to 100-1000 atm and in lyophilic systems, especially for particles with flat surfaces. In the latter case, the increase in the work of adhesion under normal conditions is comparable to kT, even for particles of approximately 10 nm size. This allows the thermodynamic stability of suspensions of such particles close to the stability limit to be controlled by changing the pressure.