Schedule May 27, 2011
Probing Swollen Polymer Structure with Single-Molecule Elasticity Experiments
Dustin McIntosh (UCSB)

D. B. McIntosh1, A. Dittmore2, O. A. Saleh2,3
(1) Physics Dept., University of California, Santa Barbara
(2) Materials Dept., University of California, Santa Barbara
(3) BMSE Program, University of California, Santa Barbara

Although long, flexible polymers form self-avoiding random walks when free in solution, most single-molecule stretching experiments elongate the polymer into a highly-aligned geometry, and prevent the long-range interactions that lead to polymer swelling. Here, we report low-force single-molecule stretching data and quantify the effects of swelling on various flexible polymers: Charged, denatured single-stranded DNA shows an immediate transition from extended chain at high forces to a swollen chain at low forces. Measurement of the salt-dependent crossover between these regimes permits estimate of how the polymer’s properties depend on electrostatics. In contrast, charge-neutral synthetic PEG molecules show a distinct ideal-to-swollen transition at a critical chain size. Single-stranded DNA composed entirely of adenine bases (poly(dA)) cooperatively base stacks; and thus, at low forces, the polymer has stiff base-stacked domains interspersed with domains of swollen coils, indicated by an elastic response that is intermediate between ideal and self-avoiding. These data permit estimates of intrinsic, microscopic properties such as the Kuhn length and excluded volume of polymers which have value in understanding their low (to zero) force structure.

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