MICRO AND NANOSCALE SYSTEMS - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 178

Ae

−s r

C

( )

Vr = −

6
6

r r

where, A and C 6 - some coefficients depending on the structure of the atom or
molecule;s - the smallest possible distance between the molecules.
In the case of two isolated molecules at a distance of r 0 the interaction force is
zero (that is, the repulsive forces balance attractive forces). When r > r 0 the resul-
tant force is the force of gravity, which increases in magnitude, reaching a maxi-
mum at r = r m and then decreases. When r > r 0 there is a repulsive force. Molecule
in the field of these forces has potential energy ( )

, which is connected with the

V r

force of ( )

f r

by the differential equation

( )

dv =− f r dr

.

At the point where r = r 0 , f(r) = 0, V(r) reachesan extremum (minimum).
The chart of such a potential is shown below in Fig. 2.1. The upper (positive)
half-axis r corresponds to the repulsion of the molecules, the lower (negative)
half-plane shows their attraction. We can now observe that at short distances the
molecules mainly repel each other.

FIGURE 2.1 Potential energy of intermolecular interaction.