Intrinsic Viscosity of Wormlike Chains with Excluded-Volume Effects

Abstract

The intrinsic viscosity [η] as a function of molecular weight M has been calculated for the Kratky‐Porod wormlike chain, taking into account excluded‐volume effects. The Peterlin theory of intrinsic viscosity was used for the calculation. The result for high molecular weights can be written [η] + b η ′ ( 1 + β′M − (1 + ε) / 2 )M 2ε = K η M (1 + 3ε) / 2 , where ε is an excluded‐volume parameter. The Kuhn statistical segment length for native double‐standard NaDNA in 0.195M [Na+] is found to be 542 Å, in fair agreement with, but somewhat lower than, the values found by other techniques. The hydrodynamic diameter of the double helix is evaluated as 79–82 Å, which is substantially higher than the value found from sedimentation coefficient measurements, and which appears physically unreasonable. Comparison with other theories of the intrinsic viscosity of wormlike coils, neglecting excluded‐volume effects, is made. The value of the Mandelkern‐Flory‐Scheraga parameter β has been calculated as 2.87 × 106, higher by about 25% than the experimental value. β is found to depend only on excluded volume and not an persistence length.