Semiflexible polymer persistence length and fluctuations
50 nm
200 nm
5
1.0
WLC theory:
⟨cos θ(s)⟩ = e^(−s/ℓ_p)
⟨R²⟩ = 2ℓ_pL[1 − ℓ_p/L(1−e^(−L/ℓ_p))]
Regime: —
R_end = — nm
R_rms = — nm
ℓ_p/L = —
Worm-like chain (WLC): the persistence length ℓ_p = κ/k_BT measures bending stiffness. DNA has ℓ_p ≈ 50 nm; F-actin ≈ 17 µm. For L ≪ ℓ_p (rigid rod), ⟨R²⟩ ≈ L². For L ≫ ℓ_p (flexible), ⟨R²⟩ ≈ 2ℓ_pL (Gaussian chain). Each chain is generated by random bending with angular noise ∝ (ds/ℓ_p)^½.