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

阴离子聚电解质链在稀溶液中与许多金属阳离子特异性地相互作用。这些相互作用最初会引起线圈的坍塌，一旦超过特征阈值，就会导致相应金属盐的沉淀。可以确定两种不同类型的阈值。一个阈值遵循相边界，这表明金属阳离子的数量随着浓度的增加而增加，对应于沉淀相应数量的聚电解质链所需的金属阳离子的化学计量量。这种趋势被称为S-Threshold。第二种行为被称为m -阈值，它遵循质量作用定律，即随着聚电解质浓度的增加，沉淀聚电解质所需的金属阳离子的数量减少。阴离子型聚丙烯酸酯链在碱土阳离子存在的稀水溶液中表现出s阈值。在接近这个阈值时，聚丙烯酸酯链坍塌成致密的颗粒，一旦超过这个阈值，这些颗粒就开始聚集。其他类型的聚电解质的类似机理细节仍然缺乏，关于聚电解质链在接近和超过m阈值时的行为的知识也是如此。此外，阴离子链是否在m阈值（或s阈值）下表现相似，独立于其化学性质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，这些方法能够通过时间分辨实验来分析过程：在大型研究设施中，采用时间分辨多角度结合静态和动态光散射和时间分辨小角度x射线分析结合小角度中子散射的方法，跟踪线圈收缩和线圈聚集，同时对相界两侧的状态进行可控寻位。这些结果有望扩展和补充我们在这一领域的薄弱知识，并首次建立了关于聚电解质线圈收缩和线圈聚集的一般原理。在聚丙烯酸酯作为调制剂存在的情况下，对无定形碳酸钙形成的时间分辨研究应作为补充。这一过程以一种理想的方式将由特异性相互作用的阳离子诱导的多电解质链的形态变化与相应的生物矿化过程联系起来。

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.