Jinfeng Dong

Aqueous phase exfoliation represents a scalable route for graphene production where aqueous media has the obvious advantage. Developing graphene-philic stabilizers is essential to achieve few layers or single layer graphene with low defects. Although aromatic moieties in surfactant tails are widely employed to facilitate the graphene exfoliation owing to π-π stacking interactions, the extent of aromatization is yet to be solved. This study designs and synthesizes a series of nonionic surfactant to investigate the effect of all aromatic tail surfactants on the aqueous phase exfoliation of graphite. The amphiphiles feature a pyrene substituted tetraphenylethylene aromatic hydrophobic core grafted with hydrophilic polyethylene glycol side chains (PsEn, n= 12, 18 and 22). With the aid of ultrasonication, a cumulative exfoliation yields of ~24.1% after 10 consecutive sediment recycling cycles is achieved. Morphological and spectroscopic techniques show that non-covalent π-π interaction between pyrene groups and graphene drives the adsorption of the conjugated aromatic cores onto graphite basal planes. The resulting aqueous dispersion is of low-defect, few-layer graphene nanosheets with long-term stability. Furthermore, freestanding composite films with structural resilience and tunable wetting can be produced, demonstrating the importance of all-aromatic surfactant tail in aqueous phase exfoliation of graphene and other two-dimensional material processing.

The dispersion of carbon nanotubes (CNTs) is crucial for further their applications in biocompatible nanodevices. A series of nonionic Gemini amphiphiles containing pyrene groups, denoted as PyE_n (where n = 12, 18, and 22), were synthesized to facilitate the dispersion of multiwalled carbon nanotubes (MWCNTs) in aqueous solutions. Compared to conventional single-chain surfactant Triton X-100 (TX-100), PyE₁₈-modified MWCNTs (PyE₁₈@MWCNTs) exhibited superior dispersing capability due to enhanced π-π interactions. The characterization of PyE₁₈@MWCNTs through various techniques revealed the presence of π-π stacking interactions among the pyrene moieties and surfaces of nanocarbon tubes. The structural integrity of MWCNTs was maintained after the modification, as evidenced by Raman spectroscopy. Furthermore, PyE₁₈-modified MWCNTs demonstrated improved hydrophilicity compared with the original MWCNTs and remained stable in aqueous solutions for over 90 days. The contact angle between the modified MWCNTs film and the aqueous drop decreased from 140° to less than 30°. These findings illustrate the significance of polyaromatic structures in the development of efficient dispersants for carbon-based materials such as CNTs, graphenes, and fullerenes.

Here are described the dilution-driven gel-sol-gel-sol transitions in aromatic hydrotrope/zwitterionic surfactant bi-component aqueous mixtures. Long and entangled wormlike micelles (WLMs) of concentrated erucyl dimethyl amidopropyl betaine (EAPB) solutions sequentially transform into hexagonal liquid crystal phase (H₁), highly concentrated spherical micelles (HCSMs), and finally hexagonal close packed micellar phase (HCP) upon gradual introducing an aromatic hydrotrope, sodium salicylate (NaSal). The HCP then successively converts into HCSMs, WLMs, and spherical micelles (SMs) upon further dilution with water, corresponding to a gel-sol-gel-sol transition. This dilution-induced HCSMs to WLMs transition results in an interesting thickening process, which is caused by a slow kinetic process, from the agglomeration and recombination of SMs to long and rigid WLMs via the intermediately formed rodlike micelles. In this work, the sustained adjustment of the competitive self-sorting and co-assembly between hydrotropes and surfactants by dilution was identified, benefitting the creation and application of WLMs fluids with switchable viscosity.

Soft-oxometalates (SOMs) are colloid suspensions of superstructured assemblies of polyoxometalates (POMs) and are found to be very effective photo-catalysts in a number of chemical reactions. The stabilization of SOMs generally requires legends or stabilizers, e.g., polymers and surfactants. In this paper, a light responsive azobenzene surfactant, C₁₀AZOC₂N₃, was developed and used to stable {Mo₁₃₂} SOMs. Various techniques such as Dynamic light scattering, TEM, UV-Vis spectra and cyclic voltammetry were employed to characterize the experimental results. The outstanding structure-directing effect of surfactant self-assembly micelles in solution on inorganic counter-anions was demonstrated. Different amount of cyclohexane was solubilized into C₁₀AZOC₂N₃ micelles to successfully control the size of {Mo₁₃₂} SOMs cluster. Furthermore, the clusters exposed to UV light for a certain time can be served as a second trigger to control the size of SOMs due to the trans-cis conformation transition of surfactant molecules. The redox potentials of C₁₀AZOC₂N₃-{Mo₁₃₂} SOMs were investigated as the cluster size varied. Interestingly, the redox potential of {Mo₁₃₂} was not affected by the cluster size, indicating that the presence of surfactant did not change the main function of {Mo₁₃₂} as an electrochemical catalyst, but merely assisted in the size control of SOM aggregation.

Herein, a new family of aggregation-induced emission (AIE) amphiphilic copolymers, named poly(N-(2-methacryloyloxyethyl)pyrrolidone)-b-poly(lauryl methacrylate-co-1-ethenyl-4-(1,2,2-triphenylethenyl)benzene), PNMP_x-b-P(LMA_y-co-TPE_z), was developed by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. The polymerization degree x of the NMP segment was kept constant at 35, whereas that of the LMA segment ranged from 9 to 55 with the polymerization degree ratio y/z of the LMA and TPE segments being around 9. As a result, the PNMP_x-b-P(LMA_y-co-TPE_z) copolymer gradually transformed from being water soluble to oil soluble with an increase in the length of the P(LMA_y-co-TPE_z) segment. Moreover, these copolymers could form self-organized normal and reverse assemblies in both water and n-dodecane. Various morphologies, including spherical micelles, worm-like micelles and vesicles, were confirmed by the transmission electron microscopy (TEM) observation. Specifically, the micelle-to-vesicle transition via worm-like micelles occurred in the aqueous solution upon increasing the length of the P(LMA_y-co-TPE_z) segment, whereas the reverse transition occurred in n-dodecane. Because of the presence of the AIE-active TPE segment, both the aqueous and the n-dodecane solutions of PNMP_x-b-P(LMA_y-co-TPE_z) were highly luminescent, and their fluorescence quantum yields significantly depended on the polarity of the solvent and the morphology of the assemblies. Due to the strong luminescence properties of PNMP_x-b-P(LMA_y-co-TPE_z) assemblies, these AIE-active amphiphilic copolymers acted as excellent bioimaging probes with high efficiency.