Intermolecular and interparticle forces
|3D Pressure-volume isotherms||2D Spreading pressure-area isotherms|
|Hisrshfelder, Fig. 4.1.1||Gaines, Fig. 4.7|
Flow properties from molecular energies
Forces near surfaces
- Bulk phases are characterized by density, free energy and entropy – not by forces.
- Molecular forces average out.
- Not so at surfaces.
(Modern) forces near sufaces
- (a) This potential is typical of vacuum interactions but is also common in liquids. Both molecules and particles attract each other.
- (b) Molecules attract each other; particles effectively repel each other.
- (c) Weak minimum. Molecules repel, particles attract.
- (d) Molecules attract strongly, particles attract weakly.
- (e) Molecules attract weakly, particles attract strongly.
- (f) Molecules repel, particles repel.
Interactions from molecular attraction
- (a) A molecule near a flat surface.
- (b) A sphere near a flat surface.
- (c) Two flat surfaces.
Derjaguin Force Approximation
Where W(D)is the energy of interaction of two flat plates.