Entropic force on a Polymer

 Several micro-manipulation techniques, such as Atomic Foce Microscopy, measure forces required to unravel specific (mostly bio-) polymers.

     

    

 

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

 Dimensional 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

"Entropic force of polymers on a cone tip," M. F. Maghrebi, Y. Kantor, M. Kardar, EPL 96, 66002 (2011)