Student(s): Sarah Lee
Project: Phase Separation and Complexation Morphology: Effects of Salt Concentration and Ion Valency
Advisor(s): Whitney Blocher McTigue
Abstract
Complex coacervation is an electrostatically driven phase separation process with broad relevance ranging from everyday applications such as salad dressings to the design of advanced materials for biomedical use. Here, we investigate coacervate systems involving polypeptoids, more specifically L-homochiral, D,L-chiral, and N-substituted polymers of lysine and glutamic acid, focusing on how ionic species influence complexation morphology. For this study we investigate how monovalent salts (NaBr, KBr) and divalent salts (MgCl₂, CaCl₂) modulate the complexation morphology. Since coacervation is driven by electrostatic interactions, the addition of salt ions can directly affect the behavior of phase separation in mixtures of oppositely charged polyelectrolytes through charge screening. The addition of salt to complexes can bias the system toward favoring solute-solvent interactions rather than solute-solute association. While previous studies have explored the effects of salt on coacervate systems, none have systematically examined polypeptides and polypeptoids in the presence of mono- and divalent salts with a focus on morphology transitions. Our findings reveal that polymer chirality, salt identity, and salt concentration each play critical roles in determining complex morphology and phase separation. We observed that all systems reach their critical salt resistance at lower concentrations with divalent salts compared to monovalent species, as the higher valence of the divalent cations results in a disproportionately larger ionic strength and more effective charge screening, thus producing more rapid morphological changes. Together, these insights provide a foundation for the rational design of drug delivery formulations, particularly those leveraging complex coacervates for encapsulation, targeted release, and stabilization.
About Sarah Lee
Major: Chemical and Biomolecular Engineering
Sarah Lee is a third-year chemical engineering student at Lehigh University. She joined Professor Blocher McTigue’s lab her sophomore year under the mentorship of PhD student Kimia Mirlohi. Her research aims to establish a foundation for the rational design of drug delivery formulations, with a focus on complex coacervation for encapsulation, targeted release, and stabilization. Beyond the lab, Lee is a Global Social Impact Fellow on the SicklED team, through which she traveled to Sierra Leone last summer to develop a low-cost diagnostic device and educational materials for sickle cell disease in low-income communities. This summer, she will intern at Merck as a Global Engineering Solutions Process Engineer, contributing to the design, construction, and delivery of advanced pharmaceutical manufacturing facilities. Lee is originally from the Washington, D.C. metropolitan area and enjoys reading, thrifting, and spending time with friends and family.