Compression and stretching of a self-avoiding chain in cylindrical nanopores

Force-induced deformations of a self-avoiding chain confined inside a cylindrical cavity, with diameter $D$, are probed using molecular dynamics simulations, scaling analysis, and analytical calculations. We obtain and confirm a simple scaling relation $-f \cdot D \sim R^{-9/4}$ in the strong-compression regime, while for weak deformations we find $f \cdot D = -A(R/R_0) + B (R/R_0)^{-2}$, where $A$ and $B$ are constants, $f$ the external force, and $R$ the chain extension (with $R_0$ its unperturbed value). For a strong stretch, we present a universal, analytical force-extension relation. Our results can be used to analyze the behavior of biomolecules in confinement.