Phase Behavior of Melts of Diblock-Copolymers with One Charged Block
Phase Behavior of Melts of Diblock-Copolymers with One Charged Block
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DOI：
10.3390/polym11061027
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发表时间：
2019-06-01
期刊：
影响因子：
5
通讯作者：
Potemkin, Igor I.
中科院分区：
文献类型：
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作者：
Gavrilov, Alexey A.;Chertovich, Alexander V.;Potemkin, Igor I.
在这项工作中，我们用具有显式静电相互作用的耗散粒子动力学方法研究了具有一个带电嵌段的嵌段共聚聚合物熔体的相行为。我们假设所有的Flory-Huggins chi参数都等于0。结果表明，单靠电荷相关吸引可以引起长程有序的微相分离；通过改变不带电块的体积分数和静电相互作用参数lambda(无量纲Bjerrum长度)构建了相图。将得到的相图与不同嵌段微珠之间具有非零X参数的等效中性两嵌段共聚物的相图进行了比较。通过将反离子接枝到带电嵌段的相应共离子上，进一步关闭静电相互作用，构建了中性共聚物。令人惊讶的是，这些相图之间的差异是相当细微的；观察到了相同顺序的相同相，如果将Lambda参数视为有效的X参数，则有序-无序转变ODT点的位置是相似的。接下来，我们研究了片层结构的ODT位置与链长N的关系。结果表明，对于不带电荷的两嵌段共聚物，产物chi N-cr几乎与N无关，而对于带有一个带电嵌段的两嵌段共聚物，我们观察到随着N的增加，波长N-cr显著增加。这可以归因于这样一个事实，即反离子熵阻止了有序结构的形成，并且它的影响对于较长的链更加明显，因为它们经历了在较小的lambda值处向有序结构的转变，当静电能量变得与k(B)T相当时，这可以通过研究带电嵌段和反离子与带电单体单元交联的两嵌段共聚物中的ODT来支持。这类体系的ODT值明显较低，且在较长的链长N时差异更为明显。即使在零的情况下也能观察到微相分离的事实可用于创建高CHI共聚物：带电基团(例如，离子液体)的引入可显著提高分离强度。研究了反离子在有序结构中的扩散，并与具有相同带电基数但均匀结构的体系进行了比较，发现在均匀结构中，沿层片面的扩散系数高于任何方向。
In this work, we investigated the phase behavior of melts of block-copolymers with one charged block by means of dissipative particle dynamics with explicit electrostatic interactions. We assumed that all the Flory-Huggins chi parameters were equal to 0. We showed that the charge- correlation attraction solely can cause microphase separation with a long-range order; a phase diagram was constructed by varying the volume fraction of the uncharged block and the electrostatic interaction parameter lambda (dimensionless Bjerrum length). The obtained phase diagram was compared to the phase diagram of equivalent neutral diblock-copolymers with the non-zero chi-parameter between the beads of different blocks. The neutral copolymers were constructed by grafting the counterions to the corresponding co-ions of the charged block with further switching off the electrostatic interactions. Surprisingly, the differences between these phase diagrams are rather subtle; the same phases in the same order are observed, and the positions of the order-disorder transition ODT points are similar if the lambda-parameter is considered as an effective chi-parameter. Next, we studied the position of the ODT for lamellar structure depending on the chain length N. It turned out that while for the uncharged diblock copolymer the product chi N-cr was almost independent of N, for the diblock copolymers with one charged block we observed a significant increase in lambda N-cr upon increasing N. This can be attributed to the fact that the counterion entropy prevents the formation of ordered structures, and its influence is more pronounced for longer chains since they undergo the transition to ordered structures at smaller values of lambda, when the electrostatic energy becomes comparable to k(b)T. This was supported by studying the ODT in diblock-copolymers with charged blocks and counterions cross-linked to the charged monomer units. The ODT for such systems was observed at significantly lower values of lambda, with the difference being more pronounced at longer chain lengths N. The fact that the microphase separation is observed even at zero Flory-Huggins parameter can be used for the creation of high-chi copolymers: The incorporation of charged groups (for example, ionic liquids) can significantly increase the segregation strength. The diffusion of counterions in the obtained ordered structures was studied and compared to the case of a system with the same number of charged groups but a homogeneous structure; the diffusion coefficient along the lamellar plane was found to be higher than in any direction in the homogeneous structure.