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arXiv 0710.5510cond-mat.softcond-mat.stat-mech
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polymer共混物和两嵌段共聚物熔体中涨落单圈理论的重整化

Renormalization of the one-loop theory of fluctuations in polymer blends and diblock copolymer melts

Piotr Grzywacz, Jian Qin, David C. Morse

摘要:

尝试使用粗粒分子理论来计算对聚合物混合物中的相关性的无规相近似(RPA)的校正已经受到对任意截止长度{ \it即}的值的不希望的敏感性的困扰,紫外线(UV)发散我们分析了紫外发散的逆结构因子$S^{-1}(k)$预测的“一环”近似类似于在以前的几项研究中使用的。我们考虑了可混溶的均聚物共混物和无序的二嵌段共聚物熔体。我们表明,在这两种情况下,所有的UV发散的贡献可以被吸收到一个重整化的广义自洽场论(SCFT)的唯象参数的值。这一观察允许建设的紫外收敛理论的修正SCFT现象。UV发散单回路对$S^{-1}(k)$的贡献显示为以下各项的总和:(i)由有效$χ$参数的重正化产生的$k$独立贡献,(ii)由单体统计链段长度的重正化产生的$k$依赖贡献,(iii)由对单回路波动自由能的平方梯度贡献产生的与$k^{2}$成比例的贡献,和(iv)与聚合度成反比的依赖于$k$的贡献,其由链端附近和嵌段共聚物中的嵌段之间的连接附近的流体结构中的局部扰动引起。

英文摘要:

Attempts to use coarse-grained molecular theories to calculate corrections to the random-phase approximation (RPA) for correlations in polymer mixtures have been plagued by an unwanted sensitivity to the value of an arbitrary cutoff length, {\it i.e.}, by an ultraviolet (UV) divergence. We analyze the UV divergence of the inverse structure factor $S^{-1}(k)$ predicted by a `one-loop' approximation similar to that used in several previous studies. We consider both miscible homopolymer blends and disordered diblock copolymer melts. We show, in both cases, that all UV divergent contributions can be absorbed into a renormalization of the values of the phenomenological parameters of a generalized self-consistent field theory (SCFT). This observation allows the construction of a UV convergent theory of corrections to SCFT phenomenology. The UV-divergent one-loop contribution to $S^{-1}(k)$ are shown to be the sum of: (i) a $k$-independent contribution that arises from a renormalization of the effective $χ$ parameter, (ii) a $k$-dependent contribution that arises from a renormalization of monomer statistical segment lengths, (iii) a contribution proportional to $k^{2}$ that arises from a square-gradient contribution to the one-loop fluctuation free energy, and (iv) a $k$-dependent contribution that is inversely proportional to the degree of polymerization, which arises from local perturbations in fluid structure near chain ends and near junctions between blocks in block copolymers.

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