Simulations of several different coarse-grained models are used to characterize how the structure factor S(q) in melts of compositionally asymmetric diblock copolymers varies with changes in the volume fraction f of the minority block, the parameter χ_eN (where χ_e is an effective interaction parameter and N is degree of polymerization), and the invariant degree of polymerization N̅. We focus here on systems with 0.25 ≤ f < 0.5. Results obtained with several different models are consistent in the expected sense, demonstrating the validity of the corresponding states principle when applied to asymmetric copolymers. Analysis is simplified by a demonstration that the effective χ parameter for these simple models is almost independent of composition. Results are compared to renormalized one-loop theory predictions, which become rapidly less accurate with increasing asymmetry. In the absence of an adequate predictive theory, a quantitative empirical relationship is developed to describe the dependence of peak intensity on χ_eN, f, and N̅ over the range 0.25 < f < 0.5. The dependences of the peak intensity on χN in asymmetric and symmetric copolymers are qualitatively similar and exhibit a crossover from a weakly fluctuating regime in which the random-phase approximation (RPA) is nearly valid to a regime of strong composition fluctuations, with a crossover centered on the RPA spinodal value of χN. This crossover becomes noticeably sharper for more asymmetric systems, however, reflecting a more abrupt appearance of well-segregated disordered domains with increasing χ in asymmetric copolymer melts.

中文翻译：

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不对称二嵌段共聚物熔体的相关性

几种不同的粗粒度模型模拟可用于表征所述结构因子如何小号（q）在组成上不对称的二嵌段共聚物的熔体与体积分数的变化而变化˚F少数块中，参数χ的_ë Ñ（其中χ _Ë是有效的相互作用参数，N为聚合度），不变聚合度为N̅。在这里，我们专注于系统与0.25≤ ˚F<0.5。用几种不同模型获得的结果在预期意义上是一致的，证明了将相应状态原理应用于不对称共聚物时的有效性。通过证明这些简单模型的有效χ参数几乎与组成无关，可以简化分析。将结果与重新归一化的单环理论预测进行比较，后者随着不对称性的增加而迅速变得不那么准确。在不存在足够的预测理论，定量经验关系被用来描述峰值强度对χ的依赖性_ë Ñ，˚F和Ñ在范围0.25 < ˚F <0.5。峰值强度的上χ的依赖性Ñ在不对称和对称共聚物的性质上类似并且显示从弱波动制度交叉，其中，随机相位近似（RPA）几乎是有效的强组成波动的制度，用交叉上χ的RPA调幅值为中心Ñ。对于更不对称的体系，这种交叉变得更加尖锐，但是，这反映了随着不对称共聚物熔体中χ的增加，良好分离的无序域的出现更加突然。