Entropic force on a Polymer

 Many current experiments employ Atomic Foce Microscopy to measure forces required to unravel specific (mostly bio-) polymers.

 What is the entropic force on a uniform (phantom or self-avoiding) polymer?

 Deminsional analysis suggests:

 Work done in moving the tip (with polymer attached) away from the surface is

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 This work can be related to the difference in free energies, as

 Comparing the two expressions yields

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