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Stretching Homopolymers

Morrison, Greg and Hyeon, Changbong and Toan, Ngo Minh and Ha, Bae-Yeun and Thirumalai, D. Stretching Homopolymers. Macromolecules, 40 (20). pp. 7343-7353. ISSN 0024-9297 (2007)

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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〉 ∼ 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 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 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.

Item Type: Article
Identification Number: 10.1021/ma071117b
Subjects: Q Science > QD Chemistry
Research Area: Economics and Institutional Change
Depositing User: Ms T. Iannizzi
Date Deposited: 03 Oct 2013 13:31
Last Modified: 06 Apr 2016 10:05
URI: http://eprints.imtlucca.it/id/eprint/1814

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