Dynamics of Semiflexible Polymer Solutions in the Highly Entangled Regime

We present experimental evidence that the effective medium approximation (EMA), [D. C. Morse, Phys. Rev. E 63, 031502 (2001)], provides the correct scaling law of the plateau modulus G(0)proportional to rho(4/3)L(p)(-1/3) (with rho the contour length per unit volume and L(p) the persistence length) of semiflexible polymer solutions, in the highly entangled regime. Competing theories, including a binary collision approximation (BCA), instead predict G(0)proportional to rho(7/5)L(p)(-1/5). We have tested both predictions using F-actin solutions which permit experimental control of L(p) independently of other parameters. A combination of video particle tracking microrheology and dynamic light scattering yields independent measurements of G(0) and L(p), respectively. Thus we can distinguish between the two proposed laws, in contrast to previous experimental studies focused on the (less discriminating) concentration dependence.