“Hydrophobicity, Charge Density, and Salt: Expanding Chemical and Physical Understanding of Complex Coacervates”

Prof. Jennifer Laaser,
Department of Chemistry,
University of Pittsburgh

Prof. Jennifer Laaser, Department of Chemistry, University of Pittsburgh

Abstract: Understanding the chemical and physical interactions that govern their physical properties of complex coacervates is critical for targeted materials design.  In this talk, I will present two aspects of our group's recent work in this area.  First, I will discuss our work on understanding how chemical features of the polyelectrolyte chains affect the phase behavior and relaxation times of these materials.  We have shown, using a synthetic approach that allows synthesis of compositionally-varied polyelectrolyte libraries from a common polymer backbone, that the properties of complex coacervates depend strongly on the charge density of the polymers, but not on the hydrophobicity of the nonionic sidechains.  Second, I will discuss our group's recent work on understanding the salt-dependent viscoelastic properties of complex coacervates.  The polymer and salt concentrations in coacervates are typically strongly coupled, and both may affect the relaxation dynamics of these materials.  To address this challenge, we have developed a "salt-addition" method for preparing complex coacervates in which the salt concentration can be increased independently of the polymer concentration.  Using this method, we have shown that the relaxation times of PSS/PDADMAC coacervates scale significantly more strongly with polymer volume fraction than typically assumed.  Finally, I will discuss the onset of a second phase separation process at high salt concentrations, bringing new complexity to the phase diagram of these materials.  These results demonstrate that the salt addition method is a powerful approach for exploring and identifying new behaviors of coacervates in the high salt concentration limit.