| |
|
· From the combined First and Second laws of Thermodynamics for a material under a tensile load F which causes a length change dL:
FdL = dU - TdS, i.e. F = (dU/dL)T,p - T (dS/dL)T,p
· This expression indicates that an elastic force arises from Internal Energy or Configurational Entropy changes with sample length.
· The first term for the force: (dU/dL)T,p is the elastic response of a "normal" solid, and represents the force due to the bond length changes occurring during the change in L.
· The second term, -T(dS/dL)T,p, is the contribution from the Configurational Entropy of the molecule.
· The configurational entropy of the molecule increases with the degree of "disorder" in its configuration: lowest for a straight molecule, largest for a convoluted molecule.
|
|
|
