We describe a strategy of fabricating CO2-triggered oil-in-water Pickering emulsion based on silica nanoparticles functionalized in situ by a trace amount of conventional CO2-switchable surfactant, N-(3-(dimethylamino)propyl)alkyl amide (CnPMA). By alternately bubbling CO2 and N2 at a moderate conditions (30 °C, 80 mL min–1), silica nanoparticles reversibly switch between amphipathic and hydrophilic as a result of the adsorption of ammonium (CO2) and the desorption of tertiary amine (N2). The emulsion can then be smart switched “on (stable)” and “off (unstable)”, along with homogenization, without needing cooling and heating. The switching of the current tertiary-based system is simple, moderate, and environmentally friendly, without contamination and the restriction of rigorous conditions. The surfactant concentration window of the Pickering emulsion is closely related to the length of hydrophobic tail, and the upper limit is no more than 0.20 cmc of that of the corresponding ammonium surfactant. Such a strategy is also suitable for commercial alkyl tertiary amines, without needing complicated organic synthesis.

To develop a fast, effective, and reversible strategy for phase separation and re-emulsification of the surfactant-based emulsions, a strategy for using acid/base-mediated redox reactions was established to switch the emulsions formed from a redox-responsive anionic surfactant of potassium dodecyl seleninate (C12SeO2K). Upon acidification, C12SeO2K was reduced by KI to give didodecyl diselenide (C12Se)2, a state of almost no surface or interfacial activity; upon basification, (C12Se)2 was oxidized by I2 to give C12SeO2K again. The fractional conversion of C12SeO2K in the reversible switching processes was close to 100%. Consequently, an unusually large change in interfacial tension (ΔIFT) as high as ∼27.1 mN m–1 was obtained at a wider concentration range starting from the critical micelle concentration of C12SeO2K; the highest IFT at the oil–water interface was obtained after an almost complete switch-off, giving an oil–aqueous solution interface very similar to that without any emulsifiers, which leads to the effective and fast phase separation of the C12SeO2K-based switchable emulsions.

A novel redox-switchable wormlike micellar system was developed based on a mixture of selenium-containing zwitterionic surfactant and commercially available anionic surfactant sodium dodecyl sulfate, which reversibly and quickly responds to H2O2 and vitamin C, and shows circulatory gel/sol transition, reflecting changes in aggregate morphology from entangled worms to vesicles.

A pH-switchable worm system was fabricated by simply mixing two non-surface-active compounds, N-(3-(dimethylamino)propyl)palmitamide (PMA) and citric acid (HCA), at a molar ratio of 3:1. Such a nanostructured fluid exhibits bell-shaped sol–gel–sol transitions with sequential pH variation, reflecting continuous structural transformations from sphere to worm to no aggregates.

Black titanium dioxide (TiO2) inverse opals (BTIOs) were obtained by in situ H2 reduction of white TiO2 inverse opals (WTIOs). The combination of chemical hydrogenation and well-ordered inverse opal structure provides BTIOs with a better photocatalytic activity than the structure-related WTIOs, fragments of BTIOs, and P25 under visible light.

In order to determine the structure-performance relationship of nonionic-zwitterionic hybrid surfactants, N,N-dimethyl-N-dodecyl polyoxyethylene (n) amine oxides (C12EOnAO) with different polyoxyethylene lengths (EOn, n = 1–4) were synthesized. For homologous C12EOnAO, it was observed that the critical micelle concentration (CMC), the maximum surface excess (Γm), CMC/C20, and the critical micelle aggregation number (Nm,c) decreased on going from 1 to 4 in EOn. However, there were concomitant increases in surface tension at the CMC (γCMC), minimum molecular cross-sectional area (Amin), adsorption efficiency (pC20), and the polarity ([I1/I3]m) based on the locus of solubilization for pyrene. The values of log CMC and Nm,c decreased linearly with EOn lengthening from 1 to 4, although the impact of each EO unit on the CMC of C12EOnAO (n = 1–4) was much smaller than that typically seen for methylene units in the hydrophobic main chains of traditional surfactants. Compared to the structurally related conventional surfactant N,N-dimethyl-N-dodecyl amine oxide (C12AO), C12EOnAO (n = 1–4) have smaller CMC, Amin, and CMC/C20, but larger pC20, Γm, and Nm,c with a higher [I1/I3]m. This may be attributed to the moderately amphiphilic EOn (n = 1–4) between the hydrophobic C12 tail and the hydrophilic AO head group.

Nonionic–zwitterionic hybrid surfactants, namely N,N-dimethyl-N-dodecyl polyoxyethylene (3) amine oxide, and the corresponding betaine and/or sulfobetaine, have been synthesized. Their molecule structures were characterized by means of electrospray ionization mass spectrometry and 1H nuclear magnetic resonance. Compared to the structurally related conventional amine oxide, betaine and sulfobetaine, the critical micelle concentrations of the three hybrid surfactants are one order of magnitude smaller than those of traditional ones. The polyoxyethylene segment between the hydrophilic head group and the hydrophobic tail makes the surface activities of the hybrid surfactants superior to their structure-related counterparts.

•Creation of thousands of plasmonic Au NPs–resin core–shell spheres per gram.•Scalable fabrication under mild conditions without using any expensive equipment.•Each as-synthesized Au NPs–resin sphere could be an easy-to-use SERS substrate.•Higher reproducible enhancement effect enabled by densely well-ordered Au NPs.•Qualitative detection of pesticide paraquat with a low detection limit of 10−12 M.Efficient, scalable, and cost-effective self-assembly of Au nanoparticles (NPs) into close-packed arrays on the surfaces of thiol-functionalized resin spheres under mild conditions was demonstrated. The resulting Au NPs–resin spheres possessed a structure in which the densely packed Au NPs monolayer and the resin bead are the shell and the core, respectively. Each Au NPs–resin sphere could be used as a surface-enhanced Raman scattering (SERS) substrate with high SERS-enhancing capacity and reproducibility. The SERS enhancement factor (EF) was estimated at 109–1011 by using thiophenol as the probe. The spatial and sphere-to-sphere variations in SERS EF were <18%. The SERS-enhancing capacity could be tuned by varying the Au NPs size. The detection limit of paraquat in water by SERS using the as-synthesized Au NPs–resin as active substrate was ∼10−12 M. The fabrication method could be a promising alternative to the preparation of well-ordered NPs arrays for SERS-active substrates.

•Periodic metal nanorings and nanocrescents are templated by a scalable approach.•Non-close-packed monolayer silica colloidal crystals are used as templates.•Continuous transition from concentric to eccentric nanorings to nanocrescents.•This scalable bottom-up technology is compatible with standard microfabrication.Here, we report a scalable bottom-up approach for fabricating periodic arrays of metal nanorings and nanocrescents. Wafer-scale monolayer silica colloidal crystals with an unusual non-close-packed structure prepared by a simple and rapid spin-coating technology are used as both etching and shadowing masks to create nanoring-shaped trenches in between templated polymer posts and sacrificial nanoholes. Directional deposition of metals in the trenches followed by liftoff of the polymer posts and the sacrificial nanoholes results in forming ordered metal nanorings. The inner and outer radii of the final nanorings are determined by the sizes of the templated polymer posts and the silica microspheres which can be easily adjusted by tuning the spin-coating and templating conditions. Most importantly, by simply controlling the tilt angle of the substrate toward the directional metal beams, continuous geometric transition from concentric nanorings to eccentric nanorings to nanocrescents can be achieved. This new colloidal templating approach is compatible with standard semiconductor microfabrication, promising for mass-production and on-chip integration of periodic nanorings and nanocrescents for a wide spectrum of technological applications ranging from nanooptical devices and ultrasensitive biosensing to magnetic memories and logic circuits.

Four diakylimidazolium ionic liquids, namely 1-alkyl-3-dodecylimidazolium bromides ([C12Cnim]Br) with the same dodecyl long-chain tail (C12) and the short alkyl side chain (Cn, n = 1–4), were synthesized, and their molecule structures were confirmed by ESI–MS, 1H-NMR and elemental analysis. The physicochemical properties of [C12Cnim]Br (n = 1–4) were determined by means of surface tension and fluorescence probe methods, respectively. It was found that elongation of the side chain length will bring about an enhancement of surface activity. Along with the side chain length increasing, the critical micelle concentration (CMC), surface tension at CMC (γCMC), the maximum surface excess (Γm), micellar aggregation number (Nm) and micellar microenvironment polarity of [C12Cnim]Br decrease, while adsorption efficiency (pC20), surface pressure at CMC (ΠCMC), the minimum molecular cross-sectional area (Amin) at air-solution interfaces and CMC/C20 ratio increase.

Zwitterionic imidazolium-based surfactants, namely 1-carboxymethyl-3-alkyl imidazolium inner salts (CnimCM, n = 10, 12, and 14), were synthesized. Their molecule structures were characterized by means of electrospray ionization mass spectrometry (ESI–MS), 1H nuclear magnetic resonance (1H NMR) and elemental analysis. Compared to the structurally related N-alkylbetaines (CnH2n+1N+(CH3)2CH2COO−), the CMCs of CnimCM are smaller than those of N-alkylbetaines. The effect of the long-chain length on the typical physicochemical properties of CnimCM was studied. It is found that the lengthening of the long-chain enhances the surface activity of CnimCM. The tendency for CnimCM surfactants is similar to the case of the structurally related traditional zwitterionic N-alkylbetaines.

This paper deals with the synthesis and self-aggregation of a hydroxyl-functionalized imidazolium-based ionic liquid (IL) surfactant, namely 1-hydroxyethyl-3-dodecylimidazolium chloride ([C2OHC12im]Cl). The molecular structure was confirmed by means of electrospray ionization mass spectrometry (ESI–MS), 1H nuclear magnetic resonance (1H NMR) and elemental analysis. Many important physicochemical parameters, such as the critical micelle concentration (CMC), the surface tension at CMC (γCMC), the adsorption efficiency (pC20), the surface pressure at CMC (ΠCMC), the maximum surface excess (Γm), the minimum molecular cross-sectional area (Amin), the value of CMC/C20, the average number of aggregation (Nm) and the micellar microenvironment polarity were determined by surface tension-concentration curves, fluorescence spectra, and electrical conductivity. The phenomena of the second CMC, the concentration dependence of Nm, and the critical average aggregation number (Nm,c) of imidazolium-based IL surfactants are reported for the first time in this paper.

A novel zwitterionic imidazolium-based ionic liquid (IL) surfactant, 1-carboxymethyl-3-dodecylimidazolium inner salt, was synthesized. The molecule structure was confirmed by means of electrospray ionization mass spectrometry, 1H nuclear magnetic resonance and elemental analysis. The isoelectric point (pI) is 3.8 ± 0.1 at 35 ± 0.1 °C. The other important physicochemical parameters such as the critical micelle concentration (CMC), the surface tension at CMC (γCMC), the adsorption efficiency (pC20), the surface pressure at CMC (ΠCMC), the maximum surface excess (Γm), the minimum molecular cross-sectional area (Amin), the value of CMC/C20 and the average number of aggregation (Nm) were determined by surface tension and steady-state fluorescence probe methods, respectively.

Arrays of microcontainers, which allow handling and isolating a small volume of liquids, are of great technological importance in the miniaturization of analytical and bioanalytical techniques. Here we report a scalable bottom-up approach for fabricating wafer-sized, periodic arrays of metallic Petri dishes with a volume as small as 10 attoliter/dish. A monolayer, nonclose-packed colloidal crystal prepared by a spin-coating technology is first used as a structural template to create ordered microwells with vertical sidewalls. Sputtering deposition of metals on the microwells, followed by removal of template, results in the formation of isolated metallic Petri dishes. The size, separation, depth, thickness, and metal types of the resulting Petri dishes can be easily tuned by adjusting the size of the colloidal microspheres and the templating conditions. We have also demonstrated that templated gold Petri dish arrays show strong surface-enhanced Raman scattering from adsorbed benzenethiol molecules. This bottom-up technology is compatible with standard microfabrication, promising for applications ranging from biomicroanalysis to surface plasmon devices.

Here, we report a simple colloidal templating approach for fabricating surface-enhanced Raman scattering (SERS) substrates with highly reproducible enhancement over wafer-sized areas. The substrates are produced by evaporating a thin layer of gold on highly ordered silica colloidal crystal−polymer nanocomposites created by a scalable spin-coating technology. The ordered inorganic−organic composite structure induces the formation of island-type gold films. Systematic measurements and statistical analysis show that the substrates exhibit high SERS reproducibility with less than 28% standard deviation over a 4 in. wafer surface. Finite element electromagnetic modeling has also been employed to simulate SERS enhancement from these structured substrates.