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arXiv 1201.4535cond-mat.soft
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涨落/关联效应对对称二嵌段共聚物有序-无序转变的影响

Quantifying Fluctuation/Correlation Effects on the Order-Disorder Transition of Symmetric Diblock Copolymers

Jing Zong, Qiang Wang

摘要:

使用快速的非格子蒙特卡罗模拟与实验可访问的波动,我们报告的第一个系统的研究明确量化的移位的有序-无序转变(ODT)的对称二嵌段共聚物的平均场预测$χ^*$。我们的模拟是在一个正则系综与可变盒长度,以消除限制的周期性边界条件上的层状周期。在我们的模拟和平均场论中使用了完全相同的模型系统(哈密顿量);因此,ODT移位是由于后者忽略了波动/相关性。虽然发现了$χ^* / χ^*_{\rm MF} - 1 \propto \bar{\mathcal{N}}^{-k}$,其中$\bar{\mathcal{N}}$表示不变的聚合度,但$k$在$\bar{\mathcal{N}}$值附近降低,该值对应于聚合物链段作为硬球的紧密堆积,表明了短程相关效应。

英文摘要:

Using fast off-lattice Monte Carlo simulations with experimentally accessible fluctuations, we report the first systematic study unambiguously quantifying the shift of the order-disorder transition (ODT) $χ^*$ of symmetric diblock copolymers from the mean-field prediction $χ^*_{\rm MF}$. Our simulations are performed in a canonical ensemble with variable box lengths to eliminate the restriction of periodic boundary conditions on the lamellar period. Exactly the same model system (Hamiltonian) is used in both our simulations and mean-field theory; the ODT shift is therefore due to the fluctuations/correlations neglected by the latter. While $χ^* / χ^*_{\rm MF} - 1 \propto \bar{\mathcal{N}}^{-k}$ is found with $\bar{\mathcal{N}}$ denoting the invariant degree of polymerization, $k$ decreases around the $\bar{\mathcal{N}}$-value corresponding to the close packing of polymer segments as hard spheres, indicating the short-range correlation effects.

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