Difference between revisions of "Intermolecular and interparticle forces"

Revision as of 18:02, 24 September 2008

3D Pressure-volume isotherms	2D Spreading pressure-area isotherms

Hisrshfelder, Fig. 4.1.1	Gaines, Fig. 4.7

	For short time scales and simple liquids, the viscosity η can be approximated by the product of the instantaneous modulus G₀ and the relaxation time τ.
	Erying model: When the strain is generated molecules are "trapped" inside an energy barrier of size ε and "jump" to a relaxed state with the characteristic time τ. While inside the barrier, the molecule vibrates with the characteristic frequency ν of the solid.
	Combining these equations yields the Arrhenius behavior. In this case, ε is the heat of vaporization of the liquid, which is the upper bound of the energy barrier. This behavior can be seen experimentally by plotting the logarithm of viscosity as a function of the reciprocal of the temperature.

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

(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.

Israelachivili Fig.10.1

Israelachivili Fig.10.2

Israelachivili Fig.10.3

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

@@ Line 32: / Line 32: @@
 |-
 | [[Image:Vicosity_at_short_times.png |100px|]]
-| For short time scales and simple liquids.
+| For short time scales and simple liquids, the viscosity &eta; can be approximated by the product of the instantaneous modulus G<sub>0</sub> and the relaxation time &tau;.
 |-
 | [[Image:Erying_model_of_flow.png |300px|]]
-| Erying model: When the strain is generated molecules are "trapped" and "jump" to a relaxed state. [[Image:Relaxation_time_in_Eyring_model.png |150px| ]]
+| Erying model: When the strain is generated molecules are "trapped" inside an energy barrier of size &epsilon; and "jump" to a relaxed state with the characteristic time &tau;. While inside the barrier, the molecule vibrates with the characteristic frequency &nu; of the solid. [[Image:Relaxation_time_in_Eyring_model.png |150px| ]]
 |-
 | [[Image:Viscosity_with_Erying_model.png |200px| ]]
-| &nu; is the characteristic frequency in the solid and &epsilon; is the heat of vaporization of the liquid.
+| Combining these equations yields the Arrhenius behavior. In this case, &epsilon; is the heat of vaporization of the liquid, which is the upper bound of the energy barrier. This behavior can be seen experimentally by plotting the logarithm of viscosity as a function of the reciprocal of the temperature.
 |}