•The superhydrophobic property can be realized in a much quicker process (7.5 min) in aqueous solution than in ethanol.•The fabrication process of superhydrophobic metal surfaces greatly increases the safety in industrial manufacture in commercial scale.•The superhydrophobic copper surfaces show excellent corrosion resistance.A simple and safe one-step immersion method was developed to obtain the stable superhydrophobic copper surfaces with excellent corrosion resistance ability using fatty acids in water-medium instead of ethanol. An organic alkali, N,N-dimethylcyclohexylamine (DMCHA), was chosen to solve the poor solubility of fatty acids in water and the high Krafft point of carboxylate salts with inorganic counterions. The superhydrophobic property can be realized in a much quicker process (7.5 min) in aqueous solution than in ethanol (more than 2 d), which is universally feasible for the fabrication of superhydrophobic metal surfaces in industry scale, thereby greatly increasing the safety in industrial manufacture.Download high-res image (232KB)Download full-size image

In this study, gold nanoparticles (AuNPs) were modified with a negatively charged peptide, Fmoc-GCE, for use as nanocarriers of a positively charged anti-tumor drug, doxorubicin hydrochloride (DOX). The Fmoc-GCE-modified AuNPs were further used to load DOX through electrostatic interaction. A temperature-sensitive gel, chitosan (CS) gel, was chosen to act as an appropriate platform to incorporate the modified AuNPs as a drug carrier. The incorporation of AuNPs makes the complex gel exhibit SERS characteristic, showing application prospects for the detection of cancer. More importantly, this drug delivery system with rather good biocompatibility can significantly extend the release time of the incorporated drugs and possesses pH responsiveness, exhibiting the advantages of controlled release and reduced side effects.

•Ethanol has specific effect on dopamine (DA) systems.•The interactions of dopamine hydrochloride and DA with ethanol were investigated by experimental and theoretical methods.•Hydrogen bonding were formed in dopamine hydrochloride-ethanol and DA-ethanol mixtures.Cyclic voltammetry (CV), density functional theory (DFT) calculations, and atoms in molecules (AIM) analyses were performed to investigate the hydrogen bonding in dopamine-ethanol and dopamine hydrochloride-ethanol mixtures. CV results show that the anodic/cathodic peak potential of dopamine hydrochloride in ethanol is influenced by the hydrogen bonding formed in the mixtures. The DFT and AIM results indicate that the hydrogen atoms of NH3+ in dopamine hydrochloride-ethanol system are easier to interact with ethanol by hydrogen bonding than those in dopamine-ethanol system. On the contrary, the hydrogen atoms on phenolic hydroxyl groups can form stronger hydrogen bonding with ethanol in dopamine-ethanol system than in dopamine hydrochloride-ethanol system.

The aggregation properties of L-arginine (L-Arg) with the acidic form of sodium bis(2-ethyl-1-hexyl)sulfosuccinate, H-AOT, in water, were investigated in detail. Double hydrogen bonding formed between the guanidyl group on the L-Arg molecule and the –SO3H group on the H-AOT molecule. The combination of L-Arg and H-AOT through hydrogen bonding and electrostatic interaction led to the self-assembly of the mixtures. The addition of hydrophobic H-AOT to L-Arg solution modulated the hydrophobicity/hydrophilicity of the L-Arg/H-AOT complexes, resulting in an increase of the packing parameter. Accordingly, a transition of the self-assembled structure from micelles to a closed lamellar bilayer structure (vesicles) and then a bicontinuous bilayer structure (sponge phase) occurred. The microstructural transition was reflected by rheological measurements, for which significant changes in both viscosity and elasticity appeared, and this was further confirmed by Cryo-TEM and FF-TEM observations.

This work describes the gelation behaviors of a biological amphiphile, deoxycholate (DC–), in aqueous solution by adding inorganic salts and modulating pH. Electrostatic interaction and hydrogen bonding can separately act as the controlling interaction for the hydrogel formation. The hydrogels formed at higher pH (about 8.5) through introducing monovalent inorganic cations (Na+) are mainly driven by electrostatic interaction between deoxycholate species and Na+ ions. When pH is decreased, with the formation of DCA molecules, hydrogen bonding between DC– and DCA come into being another leading role to construct the hydrogels, which can induce the gels within an appropriate pH region (6.7–7.3) without inorganic cations. Gels constructed through the self-assembly of deoxycholate present diverse properties according to the difference in the main driving force. Moreover, the combination of the two important interactions can significantly enhance the gelation ability.

We demonstrate that a glutanthione-based oligopeptide, Fmoc-GCE, could self-assemble into nanofibers induced by Ag+ ions in NaOH solution. During the self-assembly process, the superfine silver nanoparticles were in situ produced on the nanofibers. On the basis of a series of characterizations, we proposed the possible mechanism of the self-assembly, for which the coordination interaction between Fmoc-GCE and Ag+ ions as well as the π–π stacking of fluorenyl groups were the main driving forces of the self-assembled nanofibers. At appropriate compositions, the 3D networks of Fmoc-GCE/NaOH/Ag+ nanofibers could further form metallogel, which was responsive to pyridine and melamine, which could coordination with Ag+ ions. Moreover, the nanofibers encapsulated with superfine silver nanoparticles exhibited catalytic ability in degradation of the azo dye and the antibacterial properties to both Gram negative (E. coli) and Gram positive (S. aureus) bacteria.

Two chiral enantiomers of histidine-derived amphiphilic gelators, (4R,6S)-UIPCA and (4S,6R)-UIPCA, were synthesized through Pictet–Spengler reaction and their gelation behaviors with different organic acids were investigated. Interestingly, the chiral enantiomers of UIPCA showed smart enantioselectivity for gelating tartaric acid enantiomers to form hydrogels with excellent mechanical strength. The TEM and SEM images demonstrated that the hydrogels were composed of networks by physical entanglement of nanofibers with high aspect ratios. The formation of nanofibers was considered to be driven by the interplay of hydrogen bonding, electrostatic attraction, and hydrophobic interaction, which was supported by XRD and FT-IR spectra. The hydrogels exhibited sensitive response to a series of external stimuli, such as temperature, metal ions, and host–guest interactions, to realize the reversible gel–sol transition. The property of the gelation was elaborated and the gelators were expected to find their applications in chiral discrimination.

Gelation behavior of lithocholate (LC–) mixed with different monovalent cations in water was detected. The hydrogels consisting of tubular networks were formed by introducing alkali metal ions and NH4+ to lithocholate aqueous solutions at room temperature. The formation of tubular structures was considered to be mainly driven by the electrostatic interaction with the assistance of a delicate balance of multiple noncovalent interactions. It is interesting that the increase in temperature can induce a significant enhancement in strength of the hydrogels, accompanied by the formation of bundles of tubules and larger size aggregates. The mechanism of the temperature-induced transition can be explained by the “salting-out” effect and the electric double layer model. The hydrogels showed very high adsorption efficiency and adsorption capability for the cationic dyes and were promising to act as toxic substance adsorbents.

Aggregation behaviors of the mixtures of lysine and fatty acids (FAs) with different chain lengths in aqueous solutions were investigated, and the self-assembled structural transition was determined in detail. Aggregates including micelles, vesicles, sponge structures, and fibers were observed by varying the compositions and the chain length of fatty acids. The sponge phase found in mixtures of octanoic acid and lysine was determined by freeze fracture-transmission electron microscope (FF-TEM). Circular dichroism (CD) signals were detected in the self-assembled structures due to the chirality of lysine molecules. The rheological properties of samples consisting of different aggregates formed by mixtures of lysine and fatty acids were measured, which provided the controlling factor of the chain length. The combined effect of noncovalent interactions including electrostatic interactions, hydrogen bonding, and hydrophobicity is supposed to be responsible for the aggregation behaviors, in which the hydrogen bonding acts as the main driving force in the self-assembled process.

Gelation of lithocholic acid (LCA) mixed with zwitterionic alkyldimethylamine oxide, (CnDMAO, n = 10, 12, 14, 16, and 18), in water was detected. Hydrogels can only form at an appropriate hydrophilic–hydrophobic balance condition (n = 12, 14, and 16) with the highest gelation capability at n = 12. Microstructures of hydrogels were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) observations, indicating that the hydrogels are formed by helically intertwined fibrils. The formation of the hydrogel fibrils was suspected to be driven by a delicate balance of multiple non-covalent interactions including hydrogen bonding, electrostatic interaction, hydrophobic interaction, and the steric effect of LCA molecules. It is very interesting that temperature changes alone can induce a reversible transition between the helical fibrils and vesicle bilayers. The breakage or reconstruction of the hydrogen bonds produced by the temperature change determined the phase structure transition, i.e., the temperature change could modify the balance of the weak interactions for the formation of hydrogels. The observation of modification of supramolecular structures via temperature change may provide an efficient strategy for the phase structure transition and also may find potential applications in biosensors, shape memory, templating of functional molecular materials, etc.

Metal–ligand coordination and hydrophobic interaction are two significant driving forces in the aggregation of mixtures of Mn+ surfactants and alkyldimethylamine oxide (CnDMAO) in aqueous solutions. The coordinated systems exhibit rich aggregation behavior. This study investigated the effect of Mn+ ions (Zn2+, Ca2+, Ba2+, Al3+, Fe3+, La3+, Eu3+, and Tb3+) and hydrophobic chains (hydrocarbon and fluorocarbon) on the formation of metal-coordinated bilayers. We found that fluorocarbon chains and branched hydrocarbon chains are preferable to the corresponding linear hydrocarbon chains for the formation of an Lα phase. Moreover, Lα phases formed by fluorocarbon chains exhibited higher viscoelasticity than ones formed by the hydrocarbons, and the bilayers formed by branched chains were rather flexible, revealing obvious undulation. The construction of bilayers was also strongly affected by metal ions due to their variable coordination ability with CnDMAO. Our results contribute to the understanding of the formation of metal-coordinated bilayers, which is driven by the interplay of noncovalent forces.

Supramolecular hydrogels were prepared in the mixtures of a chiral amphiphilic lithocholic acid (LCA) and a nonionic surfactant, dodecyldimethylamine oxide (C12DMAO), in water. With the addition of LCA to C12DMAO micellar solutions, a transition from micelles to gels occurs at room temperature. Hydrogels can form at very low concentrations (below 0.1 wt %), exhibiting a super gelation capability. The rheological measurements show a strong mechanical strength with an elastic modulus exceeding 5000 Pa and a yield stress exceeding 100 Pa. Microstructures determined by TEM, SEM, and AFM observations demonstrate that the gels are formed by intertwined helical fibrils. The formation of fibrils is induced by enormous cycles of units composed of two LCA molecules and four C12DMAO molecules driven by comprehensive noncovalent interaction, especially the hydrogen bonds produced in two reversed LCA molecules and the C12DMAOH+–C12DMAO pairs. The xerogels show excellent adsorption capability of the toxic dye with a maximum adsorption value of 202 mg·g–1.

Rich phase behavior was observed in salt-free cationic and anionic (catanionic) mixtures of a double-tailed surfactant, di(2-ethylhexyl)phosphoric acid (abbreviated as DEHPA), and tetradecyldimethylamine oxide (C14DMAO) in water. At a fixed C14DMAO concentration, phase transition from L1 phase to Lα phase occurs with increasing amounts of DEHPA. Moreover, in the Lα phase, with the increase in DEHPA concentration, a gradual transition process from vesicle phase (Lαv) to stacked lamellar phase (Lαl) was determined by cryo- and FF-TEM observations combining with 2H NMR measurements. The rheological data show that the viscosity increases with DEHPA amounts for Lαv phase samples because of the increase in vesicle density. At a certain molar ratio of DEHPA to C14DMAO, i.e., 80:250, the samples are with the highest viscoelasticity, indicating the existence of densely packed vesicles. While for Lαl phase samples, with increasing DEHPA amount, a decrease of bilayer curvature was induced, leading to a decrease of viscosity obviously. Compared with general catanionic surfactant mxitures, in addition to the electrostatic interaction of ion pairs, the transition of the microstructures is also ascribed to the formation of the hydrogen bonding (−N+–O–H···O–N−) between C14DMAO molecules and protonated C14DMAOH+, which induces the growth of aggregates and the decrease of aggregate curvatures.

The phase behavior and rheological properties of an anionic surfactant, bis(2-ethylhexyl) sulfosuccinate (AOT), mixed with a zwitterionic tetradecyldimethylamine oxide (C14DMAO) in aqueous solutions, were studied at different ratios, R = wAOT/(wC14DMAO+wAOT)wAOT/(wC14DMAO+wAOT). When R = 1, the 6.0 wt% AOT solution is two-phase with dense vesicles as the lower phase. With an increase of C14DMAO fraction (decreasing R) at a total concentration of 6.0 wt%, the lower vesicle-phase (Lαv-phase) extends to generate a single Lαv-phase. Then the Lαv-phase turns into a viscoelastic wormlike micellar phase and finally rod-like or spherical C14DMAO micelles. The wormlike micellar solutions (from R = 0.3 to 0.2) are highly viscoelastic, indicating the formation of rigid network structures. The rheological properties of the viscoelastic solutions exhibit a typical Maxwell characteristic at low and intermediate oscillatory frequencies. A pronounced temperature effect on the wormlike micellar structures can be observed by rheological studies. With an increase in temperature, the samples become less structured due to shortening of the micelles. After introducing certain additives, e.g., octanol and divalent metal ions, a transition from wormlike micellar phases to birefringent Lαv-phases was observed.Graphical abstractThe wormlike micellar phase forms at low R value in the AOT/C14DMAO/H2O system at room temperature.Research highlights► Reports of wormlike micellar phases formed by anionic surfactants are comparatively rare and have not been found in AOT-participated systems. ► The viscoelasticity of the wormlike micellar phases formed in the AOT/C14DMAO/H2O system is very high, which is scarcely found in mixed systems containing anionic surfactants with short tails. ► A phase transition from wormlike micelles to vesicles can be realized through modulating the interactions between the hydrophilic groups and hydrophobic chains by introducing cosurfactants and divalent metal ions.

A metal-ligand coordinated surfactant system formed by calcium dodecylsulfate (Ca(DS)2)/tetradecyldimethylamine oxide (C14DMAO)/H2O was studied in terms of surface tension, conductivity, negative-staining TEM, phase behavior and rheological operation. In C14DMAO solution, when Ca(DS)2 is added, metal-ligand complexes form between the Ca2+ and N→O group of C14DMAO. Under this metal-ligand driving force, different phases can be obtained at different concentrations and different ratios of Ca(DS)2 and C14DMAO. At the fixed C14DMAO concentration, L1-phase consisting of spherical micelles forms at first. With the addition of Ca(DS)2, the spherical micelles elongate to be wormlike micelles and then after an L1/Lα-two phase region, the birefringent vesicle-phase (Lαv-phase) region is observed. When Ca(DS)2 concentration continues to increase, a gel-phase region is found after the Lαv-phase region and then precipitates of undissolved Ca(DS)2 appear. The transition between different phases is affected by temperature remarkably. The wormlike micellar solutions and vesicle solutions were checked by rheological measurements and showed apparent viscoelasticity at high surfactant concentrations.

Cationic hydrocarbon surfactant, N-cetylpyridinium chloride (CPC), was mixed with an anionic fluorocarbon surfactant, 1,1,11-trihydroperfluorohendecylsulfate ammonium (THFHS). The phase behavior of CPC/THFHS mixtures in aqueous solutions was studied at the total surfactant concentration of 100 mmol L−1. From CPC-richer side, with THFHS increasing, one observes the phase behavior sequence of L1-phase, L1/Lα-phase, single slightly turbid Lα-phase, then gel-like phase and finally a two-phase region with clear L1-phase at the top and precipitates at the bottom. The Lα-phase solutions consisting of polydispersed uni-lamellar vesicles with diameters from about 30 nm to more than 500 nm and multi-lamellar vesicles with diameters of more than 1.5 μm were observed by Freeze-fracture Transmission Electron Microscopy (FF-TEM). The 1H and 19F NMR measurements have been taken to detect the interaction between the hydrocarbon surfactant and fluorocarbon surfactant of L1-phase, Lα-phase, and the gel-like phase. In this system, it is interesting to find that no precipitates form when the stoichiometry between the cationic and anionic surfactants being exactly 1, which is very different from the general catanionic hydrocarbon surfactant systems with excess salts.

The effects of hydrophilic headgroups of Ca surfactants, calcium dodecylsulfate (Ca(DS)2), calcium dodecylsulfonate (Ca(DSA)2), and calcium laurate (CaL2) and hydrophobic chains of alkyldimethylamine oxide (CnDMAO, n = 12, 14, 16) on the formation of Ca2+-ligand coordinated vesicles was investigated in detail. On the basis of phase behavior studies, rheological properties and freeze-fracture transmission electron microscope (FF-TEM) images were measured. Quite different phase behaviors were observed in different surfactant systems. For a Ca surfactant with a highly polar group, Ca(DS)2, vesicles were observed in all Ca(DS)2/CnDMAO (n = 12, 14, and 16) systems, whereas for Ca surfactant with lower polar group, Ca(DSA)2, vesicles can form in Ca(DSA)2/CnDMAO systems of n = 14 and 16 but not for n = 12. For CaL2, the surfactant with the least polar group, vesicles form only in the CaL2/C16DMAO system. The results demonstrate that in the systems formed by Ca surfactants and CnDMAO, the formation of vesicles is driven not only by interaction between Ca2+ and the N → O groups of CnDMAO but also by electrostatic and hydrophobic interactions. Vesicles prefer to form in Ca surfactants with highly polar headgroups and CnDMAO with long chain length.

In this study, gold nanoparticles (AuNPs) were modified with a negatively charged peptide, Fmoc-GCE, for use as nanocarriers of a positively charged anti-tumor drug, doxorubicin hydrochloride (DOX). The Fmoc-GCE-modified AuNPs were further used to load DOX through electrostatic interaction. A temperature-sensitive gel, chitosan (CS) gel, was chosen to act as an appropriate platform to incorporate the modified AuNPs as a drug carrier. The incorporation of AuNPs makes the complex gel exhibit SERS characteristic, showing application prospects for the detection of cancer. More importantly, this drug delivery system with rather good biocompatibility can significantly extend the release time of the incorporated drugs and possesses pH responsiveness, exhibiting the advantages of controlled release and reduced side effects.