Abstract
Complex coacervation, a liquid-liquid phase separation that occurs when two oppositely charged
polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications
including wet adhesives and drug delivery vehicles. The ultra-low interfacial tension of
coacervate systems against water is critical for such applications, and it would be advantageous if
molecular models could be used to characterize how various system properties (e.g., salt concentration)
affect the interfacial tension. In this article we use field-theoretic simulations to characterize
the interfacial tension between a complex coacervate and its supernatant. After demonstrating
that our model is free of ultraviolet divergences (calculated properties converge as the collocation
grid is refined), we develop two methods for calculating the interfacial tension from field-theoretic
simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial
pressure, and the second method estimates the change in free energy as the area between
the two phases is changed. These are the first calculations of the interfacial tension from full field theoretic
simulation of which we are aware, and both the magnitude and scaling behaviors of our
calculated interfacial tension agree with recent experiments.
