title: Molecular and structural basis of low interfacial energy of complex coacervates in water.
abstract: Complex coacervate refers to a phase-separated fluid, typically of two oppositely charged polyelectrolytes in solution, representing a complex fluid system that has been shown to be of essential interest to biological systems, as well as for soft materials processing owing to the expectation of superior underwater coating or adhesion properties. The significance and interest in complex coacervate fluids critically rely on its low interfacial tension with respect to water that, in turn, facilitates the wetting of macromolecular or material surfaces under aqueous conditions, provided there is attractive interaction between the polyelectrolyte constituents and the surface. However, the molecular and structural bases of these properties remain unclear. Recent studies propose that the formation of water-filled and bifluidic sponge-like nanostructured network, driven by the tuning of electrostatic interactions between the polyelectrolyte constituents or their complexes may be a common feature of complex coacervate fluids that display low fluid viscosity and low interfacial tension, but more studies are needed to verify the generality of these observations. In this review, we summarize representative studies of interfacial tension and ultrastructures of complex coacervate fluids. We highlight that a consensus property of the complex coacervate fluid is the observation of high or even bulk-like water dynamics within the dense complex coacervate phase that is consistent with a low cohesive energy fluid. Our own studies on this subject are enabled by the application of magnetic resonance relaxometry methods relying on spin labels tethered to polyelectrolyte constituents or added as spin labeled probe molecules that partition into the dense versus the equilibrium coacervate phase, permitting the extraction of information on local polymer dynamics, polymer packing and local water dynamics. We conclude with a snapshot of our current perspective on the molecular and structural bases of the low interfacial tension of complex coacervate fluids.
authors: Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea.
authors: YongSeok
authors: Y
authors: Jho
authors: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea.
authors: Hee Young
authors: HY
authors: Yoo
authors: Biomolecular Science and Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors: Yanxian
authors: Y
authors: Lin
authors: Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA; Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA. Electronic address: songi@chem.ucsb.edu.
authors: Songi
authors: S
authors: Han
authors: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea; School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea. Electronic address: dshwang@postech.ac.kr.
authors: Dong Soo
authors: DS
authors: Hwang