Aoli Wu

Photoresponsive Self-Assembly of Surface Active Ionic Liquid

A novel photoresponsive surface active ionic liquid (SAIL) 1-(4-methyl azobenzene)-3-tetradecylimidazolium bromide ([C14mimAzo]Br) with azobenzene located in the headgroup was designed. Reversible vesicle formation and rupture can be finely controlled by photostimuli without any additives in the aqueous solution of the single-tailed ionic liquid. The photoisomerization of the azobenzene derivative was investigated by (1)H NMR and UV-vis spectroscopy. Density functional theory (DFT) calculations further demonstrate that trans-[C14mimAzo]Br has less negative interaction energy, which is beneficial to aggregate formation in water. The incorporation of trans-azobenzene group increases the hydrophobicity of the headgroup and reduces the electrostatic repulsion by delocalization of charge, which are beneficial to the formation of vesicles. However, the bend of cis-azobenzene makes the cis-isomers have no ability to accumulate tightly, which induces the rupture of vesicles. Our work paves a convenient way to achieve controlled topologies and self-assembly of single SAIL.

Anion exchange membranes with well-defined ion transporting nanochannels via self-assembly of polymerizable ionic liquids

In this study, we present a facile method to construct highly ordered and well-defined ionic channels in anion-exchange membranes (AEMs) through in-phase photopolymerization of liquid crystals (LCs). Hexagonal and lamellar LC samples were prepared by the self-organization of polymerizable amphiphilic imidazolium-based ionic liquids. The preservation of LC nanostructures in the obtained polymeric membranes was confirmed by the combination of small-angle X-ray scattering (SAXS), polarized optical microscope (POM), and scanning electronic microscopy (SEM) measurements. Phase separations of LCs at the molecular level provided highly ordered and well-defined ionic channels for efficient anion conduction and meanwhile maintained a strong hydrophobic domain to suppress the swelling degree. The membranes synthesized in the present work provide a promising model system for understanding the idea of constructing ionic highways in AEMs through self-organization.

Multiple-Responsive Hierarchical Self-Assemblies of a Smart Supramolecular Complex: Regulation of Noncovalent Interactions

We herein report a smart amphiphilic supramolecular complex ([MimA-EDA-MimA]@[DBS]2) with stimuli-responsive self-assembly, constructed by 3-(3-formyl-4-hydroxybenzyl)-1-methylimidazolium chloride (MimACl), sodium dodecyl benzene sulfonate (SDBS), and ethylenediamine (EDA). The self-assembly of [MimA-EDA-MimA]@[DBS]2 shows triple-sensitivities in response to pH, concentration, and salt. At a low pH, only micelles are formed, which can transform into vesicles spontaneously when the pH increases to 11.8. Vesicles can gradually fuse into vesicle clusters and elongated assemblies with increasing concentration of [MimA-EDA-MimA]@[DBS]2. Chainlike aggregates, ringlike aggregates, or giant vesicles can be formed by adding inorganic salts (i.e., NaCl and NaNO3), which could be derived from the membrane fusion of vesicles. The noncovalent interactions, including π-π stacking, hydrogen bonding, and electrostatic interactions, were found to be responsible for the topology evolution of assemblies. Thus, it provides an opportunity to construct smart materials through the regulation of the role of noncovalent interactions in self-assembly.

Responsive Self-Assembly of Supramolecular Hydrogel Based on Zwitterionic Liquid Asymmetric Gemini Guest

A low-molecular-weight supramolecular hydrogel has been fabricated based on host-guest interactions between β-cyclodextrin (β-CD) and an asymmetric gemini zwitterionic liquid (ZIL) containing an azobenzene and bis(trifluoromethanesulfonyl)imide. Reversible sol-gel phase transitions were triggered by light and temperature. The binding stoichiometry, mainly noncovalent interactions in the hydrogel, photo- and thermoresponsive mechanisms, and mode of inclusion in the complex were studied in detail by NMR spectroscopy, UV/Vis spectroscopy, isothermal titration calorimetry, and control experiments. Interestingly, the β-CD in the complex can be photo-manipulated to shuttle along the guest molecule, accompanied by a change in the circular dichroism signals. Reversible switching of the conductivity accompanies the sol-gel phase transition, which demonstrates the stability of the supramolecular hydrogel and its potential application in multi-stimuli-responsive electric sensor materials.

Coassembly of a Polyoxometalate and a Zwitterionic Amphiphile into a Luminescent Hydrogel with Excellent Stimuli Responsiveness

The co-existence of electrostatic attraction and repulsion between zwitterionic amphiphile and anionic polyoxometalate (POM) promotes the formation of aqueous inorganic-organic coassemblies. Injectable, luminescent supramolecular hydrogels have been fabricated by using this novel and versatile technique. Hydrogels with different characteristics can be flexibly manipulated by adjusting the molar ratios of compounds. Interestingly, a linear relationship between the luminescence intensity and temperature accompanying the sol-gel transition was observed. In addition, the emission properties of the hydrogels were sensitive to external acid and base gasses. Such multi-stimuli responsive luminescent hydrogels provide an attractive pathway to construct intelligent optical soft materials, especially for biological sensors for which stimuli responsiveness is necessary.