When polyelectrolytes and oppositely-charged multivalent ions are mixed in aqueous solutions, they can self-assemble into an array of soft materials and complex fluids, ranging from micro- and nanoparticles, to coacervates, to macroscopic gels. Here, we describe the formation and useful/interesting properties of two such materials: (1) submicron particles formed via ionotropic gelation of the cationic polysaccharide chitosan with tripolyphosphate (TPP); and (2) coacervates prepared from mixtures of the synthetic polycation poly(allylamine hydrochloride) (PAH) with either TPP or pyrophosphate (PPi). For chitosan/TPP particles (which are widely explored as potential drug carriers) we show how, by inhibiting chitosan/TPP binding, monovalent salt (NaCl) can be used to: (1) drastically slow down the rapid ionotropic gelation process to facilitate the experimental analysis of how these particles form; (2) enhance the stability of these particles to aggregation; and (3) achieve improved control over particle size.
Unlike the gel-like chitosan/TPP ionic networks, which are both soft (with 10^3 - 10^4 Pa storage moduli) and water-rich, mixtures of PAH with TPP and PPi form high-modulus, putty-like coacervates with storage moduli above 10^5 Pa and much lower (26 - 40 wt%) water contents. These moduli and water contents evidently reflect the high ionic crosslink densities enabled by the densely-charged and flexible PAH chains, and strong PAH/PPi and PAH/TPP binding (which also imparts these coacervates with long relaxation times). Besides their bulk properties, we show that the coacervates adhere to diverse substrates (both hydrophilic and hydrophobic) and, when used as wet adhesives, deliver short-term tensile adhesion strengths above 10^5 Pa. Further, the dense crosslinking within PAH/PPi and PAH/TPP coacervates makes them strong barriers to solute diffusion and (regardless of the solute-coacervate binding strength) enables them to release small water-soluble molecules over multiple months. These findings suggest that PAH/PPi and PAH/TPP coacervates can provide a simple route to both underwater adhesion and long-term controlled release.
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Intriguing transport dynamics of ethylammonium nitrate–acetonitrile binary mixtures arising from nano-inhomogeneity
Binary mixtures of ethylammonium nitrate and acetonitrile show interesting properties that originate from the structural and dynamical nano-heterogeneity present in ionic liquids. These effects are most pronounced when the ionic liquid is the minority compound. In this study the transport properties of such mixtures are studied, including viscosity, self-diffusion and conductivity. The results strongly support the presence of structural inhomogeneity and show an interesting composition-dependent behaviour in the mixtures.
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- Award ID(s):
- 1362272
- NSF-PAR ID:
- 10058242
- Date Published:
- Journal Name:
- Phys. Chem. Chem. Phys.
- Volume:
- 19
- Issue:
- 40
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 27212 to 27220
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c7cp04592a
