Predicting the phase behavior of ABAC tetrablock terpolymers: Sensitivity to Flory–Huggins interaction parameters
Predicting the phase behavior of ABAC tetrablock terpolymers: Sensitivity to Flory–Huggins interaction parameters
复制标题
DOI：
10.1016/j.polymer.2018.08.070
复制
发表时间：
2018-10
期刊：
影响因子：
4.6
通讯作者：
Akash Arora;N. Pillai;F. Bates;K. Dorfman
中科院分区：
文献类型：
--
作者：
Akash Arora;N. Pillai;F. Bates;K. Dorfman
自洽场理论是发现自组装嵌段聚合物中新的纳米结构的有力工具。然而，结果预测的可靠性很大程度上依赖于弗洛里-哈金斯相互作用参数χ，该参数用于量化不同块体混合的过剩自由能和由链段-链段相互作用产生的过剩自由能。这个问题对于多嵌段聚合物来说尤其严重，因为当不同嵌段对的χij基本不同时，χij参数众多，并且所产生的相行为很敏感。为了阐明这一问题，我们考察了poly(styrene)-b-poly(isoprene)-b-poly(styrene)‘-b-poly(ethylene氧化物(SiS’O)四嵌段三元共聚物的SCFT预测的相行为是如何改变的，这取决于用于估计该化学的χ参数的三个参数的方法。对于我们的目的来说，SIS‘O是一个理想的模型系统，因为它显示了大量的聚环氧乙烷球体形成相，由于χSO和χIO的相对较高的值而出现在聚环氧乙烷嵌段的分离中，伴随着由于聚异戊二烯和聚苯乙烯之间较小的χIS而产生的微妙的基质分离效应。我们首先使用文献中可用的χIS、χIO和χSO，它们是用平均场理论估计的相关二嵌段聚合物的有序-无序转变。由于这种方法预计会导致传播到自洽场理论中的χi的显著误差，我们还考虑了两种从两嵌段聚合物数据中提取χi的涨落校正方法，即(I)将有序-无序转变温度与分子动力学模拟预测的温度进行拟合，以及(Ii)重整化单圈理论对无序态的结构因子的预测。虽然即使是波动校正的χ参数也不能导致与实验完全匹配的超临界流体力学相行为，但使用分子动力学拟合的χ参数的超临界流体力学计算正确地预测了稳定的Frank-Kasper A15和σ相。本文介绍的结果突出了使用SCFT对多嵌段聚合物的相行为进行预测建模的挑战，这是发现新的多嵌段聚合物材料的关键任务。
Self-consistent field theory (SCFT) is a powerful tool for discovering new nanostructures in self-assembling block polymers. However, the reliability of the resulting predictions depend strongly on the Flory-Huggins interaction parametersχijused to quantify the excess free energy of mixing of different blocksiandjarising from segment-segment interactions. The problem is especially significant for multiblock polymers, owing to the multitude ofχijparameters and the sensitivity of the resulting phase behavior when theχijdo not differ substantially for different block pairs. To illuminate this issue, we examine how the SCFT-predicted phase behavior of a poly(styrene)-b-poly(isoprene)-b-poly(styrene)'-b-poly(ethylene oxide) (SIS'O) tetrablock terpolymer changes depending on the method used to estimate the trio ofχijparameters for this chemistry. SIS'O is an ideal model system for our purposes, as it exhibits a large number of poly(ethylene oxide) sphere-forming phases, emerging from the segregation of the poly(ethylene oxide) block due to the relatively high values ofχSOandχIO, accompanied by subtle matrix segregation effects arising due to the smallerχISbetween poly(isoprene) and poly(styrene). We first useχIS,χIO, andχSOavailable in the literature that were estimated using mean-field theory order–disorder transitions of the relevant diblock polymers. As this method is expected to lead to significant errors inχijthat propagate into the SCFT predictions, we also consider two fluctuation-corrected approaches to extractχijfrom diblock polymer data, namely (i) fitting the order-disorder transition temperature to that predicted by molecular dynamics simulations and (ii) renormalized one-loop theory predictions for the structure factor of the disordered state. While even the fluctuation-correctedχparameters do not lead to SCFT phase behavior that exactly matches experiments, the SCFT calculations using the molecular dynamics-fittedχparameters correctly predict stable Frank–Kasper A15 andσphases. The results presented here highlight the challenges in predictively modeling the phase behavior of multiblock polymers using SCFT, a critical task for the discovery of new multiblock polymer materials.