Linear Viscoelasticity of Polyelectrolyte Complex Coacervates

• Published in: Macromolecules Vol. 46; no. 4; pp. 1633 - 1641
• Main Authors: Spruijt, Evan, Cohen Stuart, Martien A, van der Gucht, Jasper
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.02.2013
• Subjects: Applied sciences; core micelles; diffusion; discrete relaxation; dynamic properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; polymers; Properties and characterization; ratio; rheological properties; Solution and gel properties; stability; time spectra; Viscoelasticity; Coacervate; Methacrylate polymer; Composition effect; Experimental study; Molecular relaxation; Polyelectrolyte; Stress relaxation; Amine polymer; Ionic strength; Acrylic acid polymer; Interpolymer; Aqueous solution
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma301730n

Two flexible, oppositely charged polymers can form liquid-like complex coacervate phases with rich but poorly understood viscoelastic properties. They serve as an experimental model system for many biological and man-made materials made from oppositely charged macromolecules. We use rheology to systematically study the viscoelastic properties as a function of salt concentration, chain length, chain length matching, and mixing stoichiometry of model complex coacervates of poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, and poly(acrylic acid), PAA. The dynamics of making and breaking ionic bonds between the oppositely charged chains underlie all linear viscoelastic properties of the complex coacervates. We treat (clusters of) ionic bonds as sticky points and find that there is a remarkable resemblance between the relaxation spectra of these complex coacervates and the classical sticky Rouse model for single polymer systems. Salt affects all relaxation processes in the same way, giving rise to a widely applicable time–salt superposition principle. The viscoelastic properties of the complexes are very different from those of the individual components. In the complexes with a chain length mismatch, the effect of the mismatch on the viscoelastic properties is not trivial: changing the length of the polycation affects the relaxation behavior differently from changing the length of the polyanion.