Time-resolved in-situ study of the collapse and aggregation of polyelectrolyte coils induced by specifically interacting metal cations

在稀溶液中，阴离子双链与许多金属阳离子特异性地相互作用。这些相互作用最初引起线圈的塌陷，并且一旦越过特征阈值，就引起相应金属盐的沉淀。可以确定两种不同类型的阈值。一个阈值遵循相边界，其指示金属阳离子的量随着浓度的增加而增加，所述浓度对应于沉淀相应量的双链所需的金属阳离子的化学计量量。这种趋势称为S阈值。第二种类型的行为，表示为M-阈值，服从质量作用定律，其中沉淀聚电解质所需的金属阳离子的量随着聚电解质浓度的增加而减少。阴离子聚丙烯酸酯链在稀水溶液中碱土金属阳离子存在下表现出S-阈值。在接近该阈值时，聚丙烯酸酯链塌缩成致密颗粒，一旦越过阈值，这些颗粒就开始聚集。类似的机制细节，从其他类型的聚电解质仍然缺乏知识的行为时，接近和跨越M-阈值的双链。此外，阴离子链是否在M阈值（或S阈值）下表现相似的问题，与其化学性质无关，是一个完全未解决的问题。正是这些悬而未决的问题，将在拟议的项目中通过应用新的散射方法来回答，能够通过时间分辨实验来分析过程：时间分辨多角度组合静态和动态光散射和时间分辨小角度x-在大规模的研究设施中，应采用射线分析和小角中子散射相结合的方法来跟踪线圈的收缩和线圈的聚集，以受控的方式在相边界的两侧上的状态。这些结果有望扩展和补充我们在该领域的知识，并首次建立聚电解质线圈收缩和线圈聚集的一般原则。该研究应辅以在聚丙烯酸酯作为调节剂的情况下无定形碳酸钙形成的时间分辨研究。这一过程以理想的方式将由特异性相互作用的阳离子引起的生物矿化链的形态变化与相应的生物矿化过程相关联。

Anionic polyelectrolyte chains interact specifically with a number of metal cations in dilute solution. These interactions initially induce a collapse of the coils and cause a precipitation of the corresponding metal salt once a characteristic threshold is crossed. Two different types of thresholds could be identified. One threshold follows a phase boundary, which indicates an increase of the amount of metal cations with increasing concentration corresponding to a stoichiometric amount of metal cations required to precipitate the respective amount of polyelectrolyte chains. This trend is called S-Threshold. The second type of behavior, denoted as M-threshold, obeys the law of mass action, where the amount of metal cations necessary to precipitate the polyelectrolytes decreases with the increasing concentration of polyelectrolytes. Anionic polyacrylate chains exhibit a S-threshold in the presence of alkaline earth cations in dilute aqueous solution. Upon approaching this threshold, the polyacrylate chains collapse to compact particles, which start to aggregate once the threshold is crossed. Similar mechanistic details from other types of polyelectrolytes are still lacking as does the knowledge on the behavior of polyelectrolyte chains upon approaching and crossing the M-threshold. Also, the question whether anionic chains behave similar at an M-threshold (or an S-threshold), independent of its chemical nature is an entirely unsolved problem. It is these open questions, which shall be answered in the proposed project by applying new scattering methodologies, capable of analyzing the processes by time-resolving experiments: Time-resolved multi-angle combined static and dynamic light scattering and time-resolved small angle x-ray analysis in combination with small angle neutron scattering at large scale research facilities shall be applied to follow coil shrinking and coil aggregation while addressing states on both sides of phase boundaries in a controlled way. The results are expected to extend and supplement our poor knowledge in the field and to establish for the first time general principles on coil shrinking and coil aggregation of polyelectrolytes. The study shall be complemented by a time-resolved study of the formation of amorphous calcium carbonate in the presence of polyacrylate as a modulator. This process correlates in an ideal way the morphological changes in polyelectrolyte chains induced by specifically interacting cations with the corresponding process of biomineralisation.