ma7b02031_si_001.pdf (421.16 kB)
Influence of Hydrophobicity on Polyelectrolyte Complexation
journal contribution
posted on 2017-11-16, 15:18 authored by Kazi Sadman, Qifeng Wang, Yaoyao Chen, Bavand Keshavarz, Zhang Jiang, Kenneth R. ShullPolyelectrolyte
complexes are a fascinating class of soft materials
that can span the full spectrum of mechanical properties from low-viscosity
fluids to glassy solids. This spectrum can be accessed by modulating
the extent of electrostatic association in these complexes. However,
to realize the full potential of polyelectrolyte complexes as functional
materials, their molecular level details need to be clearly correlated
with their mechanical response. The present work demonstrates that
by making simple amendments to the chain architecture, it is possible
to affect the salt responsiveness of polyelectrolyte complexes in
a systematic manner. This is achieved by quaternizing poly(4-vinylpyridine)
(QVP) with methyl, ethyl, and propyl substituentsthereby increasing
the hydrophobicity with increasing side chain lengthand complexing
them with a common anionic polyelectrolyte, poly(styrenesulfonate).
The mechanical behavior of these complexes is compared to the more
hydrophilic system of poly(styrenesulfonate) and poly(diallyldimethylammonium)
by quantifying the swelling behavior in response to salt stimuli.
More hydrophobic complexes are found to be more resistant to doping
by salt, yet the mechanical properties of the complex remain contingent
on the overall swelling ratio of the complex itself, following near
universal swelling–modulus master curves that are quantified
in this work. The rheological behaviors of QVP complex coacervates
are found to be approximately the same, only requiring higher salt
concentrations to overcome strong hydrophobic interactions, demonstrating
that hydrophobicity can be used as an important parameter for tuning
the stability of polyelectrolyte complexes in general, while still
preserving the ability to be processed “saloplastically”.