(523a) A High-Throughput Study of Polyelectrolyte Complex Coacervate Rheology and Structures

Coacervates are formed from mixing water-soluble polyelectrolytes of the opposite charge in the presence of salts and water. Despite their ubiquity in nature and wide range of applications, their physical properties such as rheology remains elusive. Obstacles to a comprehensive understanding of what drives their formation and universal scaling of their rheological properties include the large number of parameters that influence coacervate behaviors and the difficulty to control them. Coacervates typically forms from phase separation, and their properties are sensitive to ion- and monomer-specific interactions, as well as processing and kinetics. Here we present an automated data acquisition and analysis platform that aims at addressing these issues, by carrying out experiments in-situ, imaging the full sample volume and tracking system changes over long period of time.

Mechanical properties are probed by passive probe microrheology. For analysis, we pioneer the differential dynamic microscopy with uncertainty quantification (DDM UQ) which enables fast, fully automated analysis of sample viscoelasticity. Our approach reduces the computation by 99% compare to the original approach; the increased computational efficiency allows a wide range of parameters to be investigated, in real-time, with no user input. Using a fully automated, high precision stage and automated data collection routines, we also gather a time series of tiled images and use these to track the evolution of the coacervate morphology over time. The morphology data are categorized and cross-correlated with the rheology to answer the question: What is the influence of viscoelasticity on phase separation, and vice versa?

We further show that our approach can systematically illuminate the effects of a number of factors: composition, temperature, degree of polymerization, processing conditions and aging. This system is a simple and effective playground to explore driving factors for phase separation on micro and macro length scales, and potentially setting up the stage for translating monomer chemical sequence to physical material properties.