Intermolecular and interparticle forces

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Revision as of 16:55, 22 September 2008 by Morrison (Talk | contribs) (Interactions from molecular attraction)

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Intermolecular energies

3D Pressure-volume isotherms 2D Spreading pressure-area isotherms
Hirschfelder Fig 4-1-1.gif Gaines Fig 4-7.gif
Hisrshfelder, Fig. 4.1.1 Gaines, Fig. 4.7






Flow properties from molecular energies

Vicosity at short times.png For short time scales and simple liquids.
Erying model of flow.png Erying model: When the strain is generated molecules are "trapped" and "jump" to a relaxed state. Relaxation time in Eyring model.png
Viscosity with Erying model.png ν is the characteristic frequency in the solid and ε is the heat of vaporization of the liquid.






Forces near surfaces

  • Bulk phases are characterized by density, free energy and entropy – not by forces.
  • Molecular forces average out.
  • Not so at surfaces.

Galileo Surface Forces.png Galileo reference.png







(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.

Israelachvili Fig 10-1.gif
Israelachivili Fig.10.1






Interactions from molecular attraction

Eqn molecular attraction.png
Israelachvili Fig 10-2.gif
Israelachivili Fig.10.2

  • (a) A molecule near a flat surface.
  • (b) A sphere near a flat surface.
  • (c) Two flat surfaces.


Eqn Molecule surface attraction.png
Eqn Sphere Surface Attraction.png
Eqn Surface Surface Attraction.png






Derjaguin Force Approximation

Israelachvili Fig 10-3.gif
Israelachivili Fig.10.3
Eqn Derjaguin Force Equation.png
Eqn Derjaguin Force Equation-II.png

Where W(D)is the energy of interaction of two flat plates.







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