Stretching Homopolymers

Force induced stretching of polymers is important in a variety of contexts. We have used theory and simulations to describe the response of homopolymers, with N monomers, to force (f) in good and poor solvents. In good solvents and for sufficiently large N we show, in accord with scaling predictions, that the mean extension along the f axis 〈Z〉 ∼ f for small f , and 〈Z〉 ∼ f 2 3 (the Pincus regime) for intermediate values of f . The theoretical predictions for 〈Z〉 as a function of f are in excellent agreement with simulations for N = 100 and 1600. However, even with N = 1600, the expected Pincus regime is not observed due to the the breakdown of the assumptions in the blob picture for finite N . We predict the Pincus scaling in a good solvent will be observed for N & 105. The forcedependent structure factors for a polymer in a poor solvent show that there are a hierarchy of structures, depending on the nature of the solvent. For a weakly hydrophobic polymer, various structures (ideal conformations, self-avoiding chains, globules, and rods) emerge on distinct length scales as f is varied. A strongly hydrophobic polymer remains globular as long as f is less than a critical value fc. Above fc, an abrupt first order transition to a rod-like structure occurs. Our predictions can be tested using single molecule experiments. 1 ar X iv :0 70 5. 30 29 v1 [ co nd -m at .s of t] 2 1 M ay 2 00 7