Phase behavior of aqueous polyacrylic acid solutions using atomistic molecular dynamics simulations of model oligomers

We have performed fully atomistic molecular dynamics simulations of aqueous solutions of a weak, pH-responsive polyelectrolyte, polyacrylic acid (PAA). Model oligomers of PAA of different tacticities, molecular weights, degrees of deprotonation, and deprotonation patterns are simulated with water mo...

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Bibliographic Details
Published in:Polymer (Guilford) 2017-04, Vol.114, p.266-276
Main Authors: Katiyar, Ratna S., Jha, Prateek K.
Format: Article
Language:English
Subjects:
Aggregates
Aqueous solutions
Atomistic simulations
Chains
Chemical bonds
Computer simulation
Drug delivery
Drug delivery systems
Drug development
Hydrogen bonding
Hydrogen bonds
Hydrogen ions
Mathematical models
Molecular dynamics
Molecular weight
Oligomers
pH effects
Phase behavior
Phase transitions
Polyacrylic acid
Polyelectrolytes
Segments
Tacticity
Water chemistry
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Summary:We have performed fully atomistic molecular dynamics simulations of aqueous solutions of a weak, pH-responsive polyelectrolyte, polyacrylic acid (PAA). Model oligomers of PAA of different tacticities, molecular weights, degrees of deprotonation, and deprotonation patterns are simulated with water molecules. Deprotonation of PAA chains that occurs with an increase in pH results in an increase in Coulomb repulsion between chain segments on one hand, and a non-monotonic change in the hydrogen bonding between chain segments on the other hand. Consequently, at the single chain level, PAA chains are stretched at higher pH values, where the amount of stretching varies with chain tacticity. For the multiple chains case, PAA forms aggregates at higher concentrations, which are relatively denser and contain lesser water (solid-like) at lower pH than compared to higher pH (liquid-like). Such phase transitions of PAA aggregates with pH has possible implications in the design of pH-responsive polyelectrolytes for applications in drug delivery. [Display omitted] •Atomistic MD simulations of polyacrylic acid (PAA) have been performed.•We study the effects of tacticity, concentration, and pH on the phase behavior.•Aggregates form at high concentrations and their water content increase with pH.•Results of this study may be useful for the design of pH-responsive drug carriers.
ISSN:0032-3861
1873-2291
DOI:10.1016/j.polymer.2017.03.007