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The phase behavior and chain conformational structure of biphasic polyzwitterion–polyelectrolyte coacervates in salted aqueous solution are investigated with a model weak cationic polyelectrolyte, poly(2-vinylpyridine) (P2VP), whose charge fraction can be effectively tuned by pH. It is observed that increasing the pH leads to the increase of the yielding volume fraction and the water content of dense coacervates formed between net neutral polybetaine and cationic P2VP in contrast to the decrease of critical salt concentration for the onset of coacervation, where the P2VP charge fraction is reduced correspondingly. Surprisingly, a single-molecule fluorescence spectroscopic study suggests that P2VP chains upon coacervation seem to adopt a swollen or an even more expanded conformational structure at higher pH. As the hydrophobicity of P2VP chains is accompanied by a reduced charge fraction by increasing the pH, a strong pH-dependent phase and conformational behaviors suggest the shift of entropic and enthalpic contribution to the underlying thermodynamic energy landscape and chain structural dynamics of polyelectrolyte coacervation involving weak polyelectrolytes in aqueous solution. 

Polyethylene oxide (PEO)-based polymers are commonly studied for use as a solid polymer electrolyte for rechargeable Li-ion batteries; however, simultaneously achieving sufficient mechanical integrity and ionic conductivity has been a challenge. To address this problem, a customized polymer architecture is demonstrated wherein PEO bottle-brush arms are hyperbranched into a star architecture and then functionalized with end-grafted, linear PEO chains. The hierarchical architecture is designed to minimize crystallinity and therefore enhance ion transport via hyperbranching, while simultaneously addressing the need for mechanical integrity via the grafting of long, PEO chains ( M n = 10,000). The polymers are doped with lithium bis(trifluoromethane) sulfonimide (LiTFSI), creating hierarchically hyperbranched (HB) solid polymer electrolytes. Compared to electrolytes prepared with linear PEO of equivalent molecular weight, the HB PEO electrolytes increase the room temperature ionic conductivity from ∼2.5 × 10 –6 to 2.5 × 10 −5  S/cm. The conductivity increases by an additional 50% by increasing the block length of the linear PEO in the bottle brush arms from M n = 1,000 to 2,000. The mechanical properties are improved by end-grafting linear PEO ( M n = 10,000) onto the terminal groups of the HB PEO bottle-brush. Specifically, the Young’s modulus increases by two orders of magnitude to a level comparable to commercial PEO films, while only reducing the conductivity by 50% below the HB electrolyte without grafted PEO. This study addresses the trade-off between ion conductivity and mechanical properties, and shows that while significant improvements can be made to the mechanical properties with hierarchical grafting of long, linear chains, only modest gains are made in the room temperature conductivity. 

The effect of net charge of zwitterionic polymers on the phase behavior and viscoelastic properties of hybrid polyampholyte-polyoxometalate (POM) complexes in salted aqueous solutions is investigated with polyampholyte copolymers consisting of both positively and negatively charged monomers. Zwitterionic polyampholytes of varied net charge, abbreviated as PAxMy, are synthesized by varying the feeding molar ratio of negatively charged 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) to positively charged [3-(methacryloylamino) propyl]trimethylammonium chloride (MAPTAC) monomers in aqueous solution. The coacervate formation between PAxMy and inorganic anionic POM, {W12} in LiCl added aqueous solutions can be enhanced by increasing the molar fraction of positively charged MAPTAC monomer and LiCl concentration. The salt-broadened coacervation, clearly distinct from the salt-suppressed one between oppositely charged polyelectrolytes, suggests the account of zwitterion-anion pairing for PAxMy-{W12} coacervate formation due to stronger binding of multivalent {W12} giant ions with PAxMy than simple ions. Importantly, as AMPS or MAPTAC monomer fraction in polyampholytes is varied by merely ±5% from the effective net neutral case, the viscoelasticity of PAxMy-{W12} coacervates can be modified by 4-5 folds, suggesting a new tuning parameter to fine control the macroionic interactions and material properties of biomimetic complex coacervates.