蠕蟲鏈模型

蠕虫链模型（worm-like chain，WLC）是聚合物物理学中用来阐释半弹性聚合物特性的模型。是Kratky-Porod模型的后续版本。

Extensible worm-like chain model

When extending most polymers, their elastic response cannot be neglected. As an example, for the well-studied case of stretching DNA in physiological conditions (near neutral pH, ionic strength approximately 100 mM) at room temperature, the compliance of the DNA along the contour must be accounted for. This enthalpic compliance is accounted for the material parameter , the stretch modulus. For significantly extended polymers, this yields the following Hamiltonian:
,
with , the contour length, , the persistence length,  the extension and  external force. This expression takes into account both the entropic term, which regards changes in the polymer conformation, and the enthalpic term, which describes the elongation of the polymer due to the external force. In the expression above, the enthalpic response is described as a linear Hookian spring. Several approximations have been put forward, dependent on the applied external force. For the low-force regime (F < about 10 pN), the following interpolation formula was derived:
.
For the higher-force regime, where the polymer is significantly extended, the following approximation is valid:
.
A typical value for the stretch modulus of double-stranded DNA is around 1000 pN and 45 nm for the persistence length.