Gibbs energy of interaction

The negative derivative with respect to distance of the Gibbs energy of interaction per unit area yields a force per unit area between colloidal species, termed the disjoining pressure . Example In a thin liquid film, the disjoining pressure equals the pressure, beyond the external pressure, that has to be applied to the liquid in the film to maintain a given film thickness. 

Since Bernal and Fowler,16 the charging radius r0 in the Born equation has been put equal to the Inner Sphere radius, or approximately the ion to water molecule center distance plus 1.4 A. At least for 1+ ions, this gives a fairly good approximation to the Gibbs energy of interaction of the ion with the outer Dielectric Continuum if aT and s are constant throughout the medium. High-valency ions are discussed in Section IV. 

The behaviour of 77(h), already encountered in the previous section, is the most central theme of colloid stability and this issue will be dealt with extensively in Volume rv. Here, we shall emticipate this discussion by reviewing the main elements. The disjoining pressure was already introduced in sec. 1.4.2. For two colloidal particles, or macroscopic phases, a distamce h apart, let the Gibbs energy of interaction be G(h). For the present purpose only the interaction between flat surfaces has to be considered. The macroscopic phases are the (mostly solid, but in some cases liquid) support S (or Lj) cind the vapour G, interacting across the liquid... 

Gibbs Energy of Interaction When two dispersed-phase species approach,... 

Potential Energy Diagram See Gibbs Energy of Interaction. 

Primary Minimum In a plot of Gibbs energy of interaction versus separation distance, there may occur two minima. The minimum occurring at the shortest distance of separation is referred to as the primary minimum, and the minimum occurring at larger separation distance is termed the secondary minimum. 

Table 4.1. IMPACT OF CHANGES IN THE GEOMETRY OF CID-cis STEROIDS OF THE DIGITALIS TYPE ON THE APPARENT GIBBS ENERGY OF INTERACTION (-AG ) WITH NaYK -ATPase PREPARATIONS FROM HUMAN HEART (HH), HUMAN BRAIN CORTEX (HB), AND GUINEA-PIG HEART (GH) REPERCUSSIONS ON THE ENERGETIC CONTRIBUTIONS OF THE SIDE-CHAINS AT C-3fi AND C-np. METHODOLOGICAL DETAILS IN [87,88].

FIGURE 13.9 Gibbs energy of interaction between two atoms as a function of their separation distance r Tq refers to the most favorable separation (= van der Waals distance). 

The Gibbs energy of interacting electrical double layers Ge[Pg.313]

FIGURE 16.5 Gibbs energy of interaction between two identical particles according to the DLVO theory. The suspending medium has (a) low, (b) intermediate, and (c) high ionic strength. 

When a monolayer of stabilizer is present in the interface, the situation is much more complicated. First, when a wave develops, the liquid in the film moves but the monolayer prevents the interface from moving along (cf. Section 17.4.2, Equation 17.22, and Section 18.3.2). Second, in thin films, colloidal interaction forces are effective, together resulting in a total Gibbs energy of interaction Ai ,G between the dispersed particles that varies with particle separation h. This subject has been discussed in some detail in Sections 16.2 and 16.3. When the perturbation is so severe that across the thin region of the film the interparticle separation is such that dAi tG(/t)/d/t > 0, the film thins until rupture. 

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