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Effects of Non-Electrostatic Intermolecular Interactions on the Phase Behavior of pH-Sensitive Polyelectrolyte Complexes
journal contribution
posted on 2020-08-28, 19:54 authored by Lu Li, Samanvaya Srivastava, Siqi Meng, Jeffrey M. Ting, Matthew V. TirrellPolyelectrolyte complexes (PECs)
offer enormous material tunability
and desirable functionalities, and consequently have found broad utility
in biomedical and material industries. While poly(acrylic acid) (PAA)
and poly(allylamine hydrochloride) (PAH) are a commonly used pairing,
various aspects of the phase behavior of PAA–PAH complexes
have not been sufficiently quantified. We present a comprehensive
experimental study depicting the binodal phase boundaries for the
PAA–PAH complexes prepared under acidic, neutral, and basic
conditions using thermogravimetric analysis, turbidimetry, and optical
microscopy. Under neutral and basic conditions, phase behaviors of
the complexes were largely similar to one another and followed general
expectations of PEC phase behavior, except for unusually high resistance
to disruption of the complex with added salt. Stable complexes are
observed up to 4 M NaCl concentrations. Under acidic conditions, strikingly
different phase behaviors of the PAA–PAH complexes were observed.
The polymer content in the complex phase increased initially, followed
by an expected decrease as salt was added to the complexes. This behavior
may result from a combination of associative phase separation of PAA
and PAH chains, influenced by electrostatic interactions, and segregative
phase separation, which can be ascribed to the influence of a combination
of the hydrophobic interactions of the aliphatic polymer backbone
and the interpolymer hydrogen bonding of un-ionized acrylic monomer
units. Our systematic investigations over a range of pH detailing
these discrepancies in the PAA–PAH phase behavior are expected
to clarify the inconsistencies among the reports in the literature
and provide the material design strategies for practical use of the
PAA–PAH complexes and multilayer assemblies.
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Keywords
associative phase separationPAAPAHphase behaviorsmaterial design strategiessegregative phase separationbinodal phase boundaries4 M NaCl concentrationsaliphatic polymer backboneun-ionized acrylic monomer unitspH-Sensitive Polyelectrolyte Comple...Non-Electrostatic Intermolecular In...PEC phase behavior
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