Effective-sphere polymer drag
= Effective-sphere polymer drag
Approximating a dilute <polymer> coil as a hydrodynamic object of size $R$ gives $D\sim k_BT/(\eta R)$. If a stipulated model uses the theta-chain end-to-end distance $R=2a\sqrt N$ as a literal solid-sphere radius, <Stokes law> gives $D=k_BT/(12\pi\eta a\sqrt N)$. The scaling matches theta-solvent hydrodynamic coupling, but a permeable coil's <hydrodynamic radius> is not generally equal to its end-to-end distance.