Structure and rheology of polyelectrolyte complex coacervates

Scattering investigations of the structure and chain conformations, and the rheological properties of polyelectrolyte complexes (PECs) comprising model polyelectrolytes are presented. The use of charged polypeptides - (poly)-lysine and (poly)-glutamic acid with identical backbones allowed for facile...

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Published inSoft matter Vol. 14; no. 13; pp. 2454 - 2464
Main Authors Marciel, Amanda B, Srivastava, Samanvaya, Tirrell, Matthew V
Format Journal Article
LanguageEnglish
Published England Royal Society of Chemistry 2018
Subjects
Chains
Chirality
Electrostatic properties
Energy storage
Glutamic acid
Hydrogen bonding
Hydrogen storage
Lysine
Molecular conformation
Polyelectrolytes
Polypeptides
Rheological properties
Rheology
Salts
Small angle X ray scattering
Storage modulus
Superposition (mathematics)
X-ray scattering
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Summary:Scattering investigations of the structure and chain conformations, and the rheological properties of polyelectrolyte complexes (PECs) comprising model polyelectrolytes are presented. The use of charged polypeptides - (poly)-lysine and (poly)-glutamic acid with identical backbones allowed for facile tuning of the system parameters, including chain length, side-chain functionality, and chirality. Systematic studies using small-angle X-ray scattering (SAXS) of liquid PEC coacervates revealed a physical description of these materials as strongly screened semidilute polyelectrolyte solutions comprising oppositely charged chains. At the same time, solid PECs were found to be composed of hydrogen-bonding driven stiff ladder-like structures. While the coacervates behaved akin to semidilute polyelectrolyte solutions upon addition of salt, the solids were largely unaffected by it. Rheology measurements of PEC coacervates revealed a terminal relaxation regime, with an unusual plateauing of the storage modulus at low oscillation frequencies. The plateau may be ascribed to a combination of instrumental limitations and the long-range electrostatic interactions contributing to weak energy storage modes. Excellent superposition of the dynamic moduli was achieved by a time-salt superposition. The shift factors, however, varied more strongly than previously reported with added salt concentration.
Bibliography:ObjectType-Article-1
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National Institute of Standards and Technology (NIST) - Center for Hierarchical Materials Design (CHiMaD)
AC02-06CH11357
US Department of Commerce
ISSN:1744-683X
1744-6848
DOI:10.1039/c7sm02041d