@article{eprints1814,
          author = {Greg Morrison and Changbong Hyeon and Ngo Minh Toan and Bae-Yeun Ha and D. Thirumalai},
         journal = {Macromolecules},
       publisher = {American Chemical Society},
            year = {2007},
           title = {Stretching Homopolymers},
          number = {20},
           pages = {7343--7353},
          volume = {40},
             url = {http://eprints.imtlucca.it/1814/},
        abstract = {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 an external 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? {$\sim$} f for small f and ?Z? {$\sim$} 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 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 {$\gtrsim$} 105. The force-dependent structure factors for a polymer in a poor solvent show that there is 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 rodlike structure occurs. Our predictions can be tested using single molecule experiments. }
}