Worm-Like Chain — Persistence Length

The worm-like chain (WLC) model describes semiflexible polymers. Each segment can bend with bending stiffness κ = k_BT·L_p/b. The tangent-tangent correlation decays exponentially: ⟨t(s)·t(0)⟩ = e^−s/L_p.

End-to-end distance: ⟨R²⟩ = 2L_pL[1 − (L_p/L)(1 − e^−L/L_p)].

DNA: L_p ≈ 50 nm. Actin: L_p ≈ 17 μm (stiff). Titin: L_p ≈ 0.4 nm (flexible coil). The WLC underpins force-extension curves measured by optical tweezers.