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

• Applicant: Professor Dr. Klaus Huber
• Subject Area: Experimental and Theoretical Physics of Polymers ; Synthesis and Properties of Functional Materials
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 231919084

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.

• DFG Programme: Research Grants