Title: Metastability in Polyelectrolyte Complexation

Polyelectrolyte complexes (PECs) are formed by the electrostatic interactions between oppositely charged polymers and have broad applications in drug delivery systems, coatings, and water treatment processes. While previous research has focused on how the order of mixing affects the stability of PECs in the dilute phase due to kinetically trapped structures, there has been limited investigation into how the mixing sequence impacts the mass of the complexes in the dense, complex phase. In this study, we investigate the effects of mixing order on the formation and stability of PECs, specifically using poly (diallyldimethylammonium chloride) (PDDA) at a final concentration of 25 mM and poly (sodium 4-styrenesulfonate) (PSS) at 3 mM. Our findings reveal that altering the order of mixing leads to significant differences in the mass of the resulting complexes. These results provide new insights into the kinetic pathways that govern PEC formation, highlighting the importance of mixing sequence as a key factor in controlling complex mass. Furthermore, we investigated the interfacial stability of PECs in macroscopic layers across various solution environments. By understanding the effects of mixing orders in different systems conditions, we provide new insights to the kinetics of polyelectrolytes complex formation, which is crucial for evaluating their various applications.