Variational theory for a single polyelectrolyte chain revisited
Variational theory for a single polyelectrolyte chain revisited
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重新审视单聚电解质链的变分理论
DOI：
10.1140/epje/i2004-10007-3
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
R. R. Netz
中科院分区：
文献类型：
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作者：
Manoel Manghi;R. R. Netz
摘要：在屏蔽作用下，我们重新考虑了静电对单个无限长电荷聚合物驻留长度的贡献。采用高斯型变分方法，只取其变分参数。对于弱电荷和柔性链，皱缩发生在较小的长度尺度上，因为构象涨落克服了静电斥力。静电持续长度取决于屏蔽长度的平方，这是Khokhlov和Khachaturian首先通过将Odijk-Skolnick-Fixman(OSF)理论应用于一串皱缩的斑点而提出的。我们将我们的方法与以前的理论工作(包括变分公式)进行了比较，结果表明，几位作者发现的结果来自于对小尺度截断的不当使用。对于高电荷链和刚性链，不会发生褶皱；在这里，我们恢复了OSF的结果，并验证了微弯杆的微扰计算。
Abstract.We reconsider the electrostatic contribution to the persistence length, $\ell_{\rm e}$, of a single, infinitely long-charged polymer in the presence of screening. A Gaussian variational method is employed, taking $\ell_{\rm e}$ as the only variational parameter. For weakly charged and flexible chains, crumpling occurs at small length scales because conformational fluctuations overcome electrostatic repulsion. The electrostatic persistence length depends on the square of the screening length, $\ell_{\rm e}\sim\kappa^{-2}$, as first argued by Khokhlov and Khachaturian by applying the Odijk-Skolnick-Fixman (OSF) theory to a string of crumpled blobs. We compare our approach to previous theoretical works (including variational formulations) and show that the result $\ell_{\rm e}\sim\kappa^{-1}$ found by several authors comes from the improper use of a cutoff at small length scales. For highly charged and stiff chains, crumpling does not occur; here we recover the OSF result and validate the perturbative calculation for slightly bent rods.