Stretching Homopolymers

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 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 $\la Z\ra$ 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 $N\gtrsim 10^5$}. The force-dependent 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 $f_c$. Above $f_c$, an abrupt first order transition to a rod-like structure occurs. Our predictions can be tested using single molecule experiments.

24 pages, 7 figures

References in corpus (1)

• Mechanical unfolding of RNA: From hairpins to structures with internal multiloops

Cited by in corpus (3)

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• Unexpected relaxation dynamics of a self-avoiding polymer in cylindrical confinement
• Tension Dynamics and Linear Viscoelastic Behavior of a Single Semiflexible Polymer Chain