



01667nas a2200145   4500008004100000245006400041210006200105260001400167490000700181520123200188100002701420700001801447700001901465856003701484       2012                        eng d00aPolymer-mediated entropic forces between scale-free objects0 aPolymermediated entropic forces between scalefree objects  c2012/12/30 v863 a  The number of configurations of a polymer is reduced in the presence of a
barrier or an obstacle. The resulting loss of entropy adds a repulsive
component to other forces generated by interaction potentials. When the
obstructions are scale invariant shapes (such as cones, wedges, lines or
planes) the only relevant length scales are the polymer size R_0 and
characteristic separations, severely constraining the functional form of
entropic forces. Specifically, we consider a polymer (single strand or star)
attached to the tip of a cone, at a separation h from a surface (or another
cone). At close proximity, such that h<<R_0, separation is the only remaining
relevant scale and the entropic force must take the form F=AkT/h. The amplitude
A is universal, and can be related to exponents \eta governing the anomalous
scaling of polymer correlations in the presence of obstacles. We use
analytical, numerical and epsilon-expansion techniques to compute the exponent
\eta for a polymer attached to the tip of the cone (with or without an
additional plate or cone) for ideal and self-avoiding polymers. The entropic
force is of the order of 0.1 pN at 0.1 micron for a single polymer, and can be
increased for a star polymer.
1 aMaghrebi, Mohammad, F.1 aKantor, Yacov1 aKardar, Mehran  uhttp://arxiv.org/abs/1208.5778v2