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PRISM Theory Study of Amphiphilic Block Copolymer Solutions with Varying Copolymer Sequence and Composition
Macromolecules ( IF 5.5 ) Pub Date : 2017-09-07 00:00:00 , DOI: 10.1021/acs.macromol.7b01419
Ivan Lyubimov 1 , Daniel J. Beltran-Villegas 1 , Arthi Jayaraman 1
Affiliation  

We present a comparison of Polymer Reference Interaction Site Model (PRISM) theory and molecular dynamics (MD) simulations for studying amphiphilic block copolymers in solution. We use a generic coarse-grained model to represent amphiphilic A–B block copolymers in implicit solvent with the solvophobicity of the B segments captured using effective B–B pairwise attraction modeled using the Lennard-Jones potential. We study the assembly of the amphiphilic A–B block copolymer as a function of solvophobicity for varying copolymer sequences (diblock and triblock) and composition (solvophobic-rich or solvophilic-rich). The PRISM theory equation along with the atomic Percus–Yevick closure is solved to obtain the intermolecular pair correlations in real space, g(r), and structure factors in Fourier space, S(k), for block copolymer solutions at increasing values of solvophobicity. The real-space intermolecular pair correlation functions and structure factors from PRISM theory and from MD simulations are compared directly. We find excellent quantitative agreement in g(r) between PRISM predictions and MD simulations at low solvophobicities where the block copolymer solution is in a disordered state. PRISM theory captures the concentration fluctuations at low solvophobicities well but fails to converge to a numerical solution at higher solvophobicities where we see evolution of ordered structures in MD simulations. Despite this drawback, PRISM theory is a valuable tool as the low solvophobicity results from PRISM predict many of the thermodynamic and structural signatures of the block copolymer solutions at higher solvophobicities. For example, we find that the inverse microphase peak 1/S(k*) at low solvophobicities obtained from PRISM theory, which when extrapolated to zero quantifies the spinodal transition solvophobicity value, is in good quantitative agreement with MD simulations. Additionally, in those systems where MD simulations predict aggregation of the micelles/clusters at high solvophobicity, the structure factors from PRISM theory at low solvophobicity also present an increasing value in the zero-wave vector structure, indicating a tendency toward macrophase separation at higher solvophobicity. These results show the capability of PRISM theory to predict assembly over a wide range of design parameters of copolymers and guide the use of computationally intensive molecular simulations.

中文翻译:

共聚物序列和组成不同的两亲嵌段共聚物溶液的PRISM理论研究

我们目前比较聚合物参考相互作用位点模型(PRISM)理论和分子动力学(MD)模拟,以研究溶液中的两亲嵌段共聚物。我们使用通用的粗粒度模型来表示隐式溶剂中的两亲性A–B嵌段共聚物,并利用Lennard-Jones势建模有效的B–B成对吸引来捕获B段的疏油性。我们研究了两亲性A–B嵌段共聚物的组装与不同共聚物序列(二嵌段和三嵌段)和组成(富疏溶剂性或富亲溶剂性)的疏溶剂性的关系。将PRISM理论方程与原子Percus-Yevick闭环一起求解,以获得真实空间中的分子间对相关性gr),以及在疏溶剂性值增加的情况下嵌段共聚物溶液在傅立叶空间中的结构因子Sk)。直接比较了PRISM理论和MD模拟得出的真实空间分子间对相关函数和结构因子。我们发现gr)在嵌段共聚物溶液处于无序状态的低疏溶剂性的PRISM预测和MD模拟之间。PRISM理论很好地捕获了低疏溶剂性下的浓度波动,但是在高疏溶剂性下未能收敛到数值解,在MD模拟中我们看到有序结构的演化。尽管存在这个缺点,PRISM理论还是一种有价值的工具,因为PRISM的低憎溶剂性结果预测了嵌段共聚物溶液在高憎溶剂性下的许多热力学和结构特征。例如,我们发现反微相峰1 / Sk *)时,从PRISM理论获得的低疏溶剂性(外推为零即可量化旋节线过渡的疏溶剂性值)与MD模拟具有良好的定量一致性。另外,在MD模拟预测高疏油性下胶束/团簇聚集的系统中,低疏油性下PRISM理论的结构因子在零波矢量结构中也呈现出越来越高的值,表明在高疏油性下有宏观相分离的趋势。这些结果表明PRISM理论具有预测各种共聚物设计参数组装的能力,并指导计算密集型分子模拟的使用。
更新日期:2017-09-07
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