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On Van der Waals Forces

  1. Sep 23, 2011 #1
    Can someone enlighten me about the quantum level explanations for the following:
    1. Adhesion between two substances
    2. Cohesion within a substance
    3. Strength of a substance (as in tensile strength, compressive strength and shear strength)
    4. Stiffness of a substance (as in Youngs modulus, Poissons ratio and shear modulus)
    5. Strain energy of materials
    6. Vibration and damping of strain energy systems
    7. Variation of inter molecular forces with tempearture (as in melting and boiling)
    8. Variation of intermolecular forces with external pressure
    9. Absence of intermolecular forces between two soilds however closely they are spaced
    Hope that I have expressed my queries clearly.
    Regards
     
  2. jcsd
  3. Sep 23, 2011 #2

    alxm

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    Science Advisor

    "van der Waals" forces, in its original and most general form, refers to essentially all intermolecular forces (except possibly hydrogen-bonding, which at least in practice is excluded even from the most general usages these days). You might want to start http://en.wikipedia.org/wiki/Intermolecular_force" [Broken].

    There certainly exists quantum-level explanations for all that, but there's no way it could be summarized in a single message-board post. You're basically asking for a complete quantum description of most chemical and material properties, which is something that encompasses several whole fields (quantum chemistry, solid-state physics). So you'd really need several whole textbooks to get the details.

    I'm not sure what you mean by (9) though. There are always intermolecular forces, even at a large distance (at the very least there are always London forces).
     
    Last edited by a moderator: May 5, 2017
  4. Sep 23, 2011 #3
    Dear Alxm, thanks for the reply.
    I am however, not asking for a complete description of most chemical and material properties. I am a structural engineer by profession and am interested only in the mechanical properties of a continuum. Besides, I am not also looking for a detailed description - sources are more than sufficient. Unfortunately, I could not dig out muc from the net, myself.
    The 9 th point is the particular position that puzzles. Please forgive me if I am wrong. Suppose, I take two bars of steel and place them extremely close side-by-side. Intutively I feel that the forces between molecules within one bar and the forces between close molecules from bar-to-bar are different. If so, what is the origin of such difference?
    I hope I have made the query clear
    Regards
     
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