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Order-Disorder Transitions and Free Energies in Asymmetric Diblock Copolymers
Macromolecules ( IF 5.1 ) Pub Date : 2020-08-23 , DOI: 10.1021/acs.macromol.0c01359 Taher Ghasimakbari 1 , David C. Morse 2
Macromolecules ( IF 5.1 ) Pub Date : 2020-08-23 , DOI: 10.1021/acs.macromol.0c01359 Taher Ghasimakbari 1 , David C. Morse 2
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Simulations of simple bead-spring models of asymmetric diblock copolymers are used to study the dependence of order-disorder transitions and free energies upon the invariant degree of polymerization N̅ and the fraction f of beads in the minority block. Well-tempered metadynamics is used to determine values of (χN)ODT along the lamellar-disorder and hexagonal-disorder transitions over the range 0.1875 ≤ f ≤ 0.5 for two models with different values of N̅ = 480 and 1920, where χ is an effective Flory–Huggins interaction parameter, N is the degree of polymerization, and (χN)ODT is a value of χN at the order-disorder transition (ODT). More extensive studies are performed for systems with f = 1/4, which undergo a hexagonal-disorder transition. Equivalent results for both phase boundaries and free energies are obtained for one pair of systems with different numbers of beads per chain but matched values of f = 1/4 and N̅, in agreement with the corresponding state hypothesis. Comparison of results for (χN)ODT for systems with f = 1/4 and several values for N̅ show a systematic decrease in (χN)ODT with an increase N̅, consistent with the expected approach to the self-consistent field (SCFT) prediction as N̅ → ∞. Results for the free energy per chain in the disordered and hexagonal phases of systems with f = 1/4 show that SCFT gives rather accurate predictions for the free energy in the ordered hexagonal phase but that the random-mixing approximation underlying SCFT significantly overestimates the free energy of the disordered phase.
中文翻译：
不对称二嵌段共聚物的有序无序跃迁和自由能
用简单的不对称二嵌段共聚物的珠-弹簧模型进行模拟，以研究有序-无序转变和自由能对聚合度N polymerization和少数嵌段中珠粒分数f的依赖性。以及回火metadynamics用于确定的值（χ Ñ）ODT沿着在范围层状-无序和六角形-无序转变0.1875≤ ˚F ≤0.5为两个模型与不同值Ñ = 480和1920，其中χ是一有效弗洛里-赫金斯相互作用参数，ñ是聚合度，和（χ ñ）ODT是的χ的值ñ在无序过渡（ODT）时。对于f = 1/4的系统，进行了更广泛的研究，该系统经历了六方无序过渡。一对系统的相界和自由能的等效结果都获得于一对系统，每对系统的珠子数不同，但是f = 1/4和N̅相匹配，与相应的状态假设相符。结果（χ的比较Ñ）ODT用于与系统˚F = 1/4和几个值Ñ显示（χ系统性降低Ñ）ODT随着Ñ，与预期的自洽场（SCFT）预测方法一致，即N̅ →∞。f = 1/4的系统的无序和六边形相中的每链自由能的结果表明，SCFT对有序六边形相中的自由能给出了相当准确的预测，但是SCFT的随机混合近似法大大高估了自由能。无序阶段的能量。
更新日期：2020-09-09
中文翻译：
不对称二嵌段共聚物的有序无序跃迁和自由能
用简单的不对称二嵌段共聚物的珠-弹簧模型进行模拟，以研究有序-无序转变和自由能对聚合度N polymerization和少数嵌段中珠粒分数f的依赖性。以及回火metadynamics用于确定的值（χ Ñ）ODT沿着在范围层状-无序和六角形-无序转变0.1875≤ ˚F ≤0.5为两个模型与不同值Ñ = 480和1920，其中χ是一有效弗洛里-赫金斯相互作用参数，ñ是聚合度，和（χ ñ）ODT是的χ的值ñ在无序过渡（ODT）时。对于f = 1/4的系统，进行了更广泛的研究，该系统经历了六方无序过渡。一对系统的相界和自由能的等效结果都获得于一对系统，每对系统的珠子数不同，但是f = 1/4和N̅相匹配，与相应的状态假设相符。结果（χ的比较Ñ）ODT用于与系统˚F = 1/4和几个值Ñ显示（χ系统性降低Ñ）ODT随着Ñ，与预期的自洽场（SCFT）预测方法一致，即N̅ →∞。f = 1/4的系统的无序和六边形相中的每链自由能的结果表明，SCFT对有序六边形相中的自由能给出了相当准确的预测，但是SCFT的随机混合近似法大大高估了自由能。无序阶段的能量。
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