化学双分散单体超分子聚合物中的无规、嵌段和交替有序
Random, blocky and alternating ordering in supramolecular polymers of chemically bidisperse monomers
摘要：
作为理解分子或化学多分散性在自组装中的作用的第一步，我们提出了一个粗粒度的模型，该模型描述了在含有两个自组装物种的溶液中自发形成的准线性聚合物。我们的理论框架是基于一个两个组件的自组装伊辛模型，其中的双分散性参数化的结合自由能的强度，取决于参与配对相互作用的单体物种。取决于所涉及的结合自由能的相对值，形成包括两种组分的组装体的不同形态，表现出顺磁性、铁磁性或反铁磁性类顺序，即，组件中两种组分的随机、块状或交替排序。分析模型的情况下，铁磁有序，这是最实际的兴趣，我们发现，从最小的组装条件的过渡到那些特征在于强聚合可以描述的临界浓度，取决于两个物种的浓度比。有趣的是，组装体中单体的分布与原始分布不同，即，加入系统的两种组分的浓度比。具有较小结合自由能的单体在短组装体中更丰富，并且具有较大结合亲和力的单体在长组装体中更丰富。在某些条件下，两种组分聚集成单独的超分子聚合物物种，并且在该意义上相分离。我们发现强烈的偏离预期的增长规律的超分子聚合物，即使是适度的第二个组件，只要它是化学上足够不同的主要。
英文摘要：
As a first step to understanding the role of molecular or chemical polydispersity in self-assembly, we put forward a coarse-grained model that describes the spontaneous formation of quasi-linear polymers in solutions containing two self-assembling species. Our theoretical framework is based on a two-component self-assembled Ising model in which the bidispersity is parameterized in terms of the strengths of the binding free energies that depend on the monomer species involved in the pairing interaction. Depending upon the relative values of the binding free energies involved, different morphologies of assemblies that include both components are formed, exhibiting paramagnetic-, ferromagnetic- or anti ferromagnetic-like order, i.e., random, blocky or alternating ordering of the two components in the assemblies. Analyzing the model for the case of ferromagnetic ordering, which is of most practical interest, we find that the transition from conditions of minimal assembly to those characterized by strong polymerization can be described by a critical concentration that depends on the concentration ratio of the two species. Interestingly, the distribution of monomers in the assemblies is different from that in the original distribution, i.e., the ratio of the concentrations of the two components put into the system. The monomers with a smaller binding free energy are more abundant in short assemblies and monomers with a larger binding affinity are more abundant in longer assemblies. Under certain conditions the two components congregate into separate supramolecular polymeric species and in that sense phase separate. We find strong deviations from the expected growth law for supramolecular polymers even for modest amounts of a second component, provided it is chemically sufficiently distinct from the main one.
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