Biomacromolecules rely on the precise placement of monomers to encode information for structure, function, and physiology. Efforts to emulate this complexity via the synthetic control of chemical sequence in polymers are finding success; however, there is little understanding of how to translate monomer sequence to physical material properties. Here we establish design rules for implementing this sequence-control in materials known as complex coacervates. These materials are formed by the associative phase separation of oppositely charged polyelectrolytes into polyelectrolyte dense (coacervate) and polyelectrolyte dilute (supernatant) phases. We demonstrate that patterns of charges can profoundly affect the charge–charge associations that drive this process. Furthermore, we establish the physical origin of this pattern-dependent interaction: there is a nuanced combination of structural changes in the dense coacervate phase and a 1D confinement of counterions due to patterns along polymers in the supernatant phase.
Complex coacervates can form through
the electrostatic complexation
of oppositely charged polymers. The material properties of the resulting
coacervates can change based on the polymer chemistry and the complex
interplay between electrostatic interactions and water structure,
controlled by salt. We examined the effect of varying the polymer
backbone chemistry using methacryloyl- and acryloyl-based complex
coacervates over a range of polymer chain lengths and salt conditions.
We simultaneously quantified the coacervate phase behavior and the
linear viscoelasticity of the resulting coacervates to understand
the interplay between polymer chain length, backbone chemistry, polymer
concentration, and salt concentration. Time-salt superposition analysis
was used to facilitate a broader characterization and comparison of
the stress relaxation behavior between different coacervate samples.
Samples with mismatched polymer chain lengths highlighted the ways
in which the shortest polymer chain can dominate the resulting coacervate
properties. A comparison between coacervates formed from methacryloyl
vs acryloyl polymers demonstrated that the presence of a backbone
methyl group affects the phase behavior, and thus the rheology in
such a way that coacervates formed from methacryloyl polymers have
a similar phase behavior to those of acryloyl polymers with ∼10×
longer polymer chains.
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