Good-solvent force-extension scaling ($R\sim Na(fa/k_{B}T{)}^{2/3}$)

For a long flexible polymer in a good solvent, a tensile blob of size ${\xi }_t\sim k_{B}T/f$ contains $g\sim ({\xi }_t/a{)}^{1/\nu }$ statistical segments. Aligning $N/g$ blobs gives $R\sim (N/g){\xi }_t=Na(fa/k_{B}T{)}^{1/\nu -1}$. The three-dimensional Flory approximation $\nu =3/5$ gives the displayed power. The regime requires $a\ll {\xi }_t\ll a{N}^{\nu }$: below its force range the coil has ordinary linear response, and above it finite link extension matters. Numerical amplitudes depend on solvent quality and segment conventions.^[ref]