期刊导航

Totally found 2762 items.

  • [期刊] Polar-Nonpolar Interfaces of Normal Bicontinuous Cubic Phases in Nonionic Surfactant/Water Systems Are Parallel to the Gyroid Surface
    We investigated the structures of normal (type I) bicontinuous cubic phases in hexa-, hepta-, and octaethylene glycol dodecyl ether/water mixtures by small-angle X-ray crystallography of single-crystal domains. Reconstructed electron densities showed that the hydrophilic chains with high electron density are confined to a film centered on the surface of the Gyroid (a triply periodic minimal surface), while hydrophobic chains with low electron density are distributed within the pair of interwoven labyrinths carved out by the Gyroid. Further, the local minimum within the high electron density region, due to bulk water, coincides precisely with the Gyroid. This minimum is less pronounced in mixtures with longer ethylene glycol chains, consistent with their decreased water content. Our analysis clearly shows that the polar-nonpolar interfaces are parallel to the Gyroid surface in all mixtures. The repulsive hydration or overlapping force between the pair of facing monolayers of ethylene glycol chains on either side of the Gyroid surface is the likely origin of the parallel interfaces.
  • [期刊] Segregation of Amine Oxide Surfactants in PVA Films
    The vertical depth distributions of amine oxide surfactants, N,N-dimethyldodecyl amine N-oxide (DDAO) and N,N-dimethyltetradecyl amine N-oxide (DTAO), in poly(vinyl alcohol) (PVA) films were explored using neutron reflectometry (NR). In both binary and plasticized films, the two deuterated surfactants formed a single monolayer on the film surface with the remaining surfactant homogeneously distributed throughout the bulk of the film. Small-angle neutron scattering and mechanical testing revealed that these surfactants acted like plasticizers in the bulk, occupying the amorphous regions of PVA and reducing its glass-transition temperature. NR revealed little impact of plasticizer (glycerol) incorporation on the behavior of these surfactants in PVA. The surfactant molecular area in the segregated monolayer was smaller for DTAO than for DDAO, indicating that the larger molecule was more densely packed at the surface. Surface tension was used to assess the solution behavior of these surfactants and the effect of glycerol incorporation. Determination of molecular area of each surfactant on the solution surface revealed that the structures of the surface monolayers are remarkably consistent when water is placed by the solid PVA. Incorporation of glycerol caused a decrease of molecular area for DDAO and increase in molecular area for DTAO both in solution and in PVA. This suggests that the head group interactions, which normally limit the minimum area per adsorbed molecule, are modified by the length of the alkyl tail.
  • [期刊] Structural Change of an alpha-Gel (alpha-Form Hydrated Crystal) Induced by Temperature and Shear Flow in an Oleic Acid Based Gemini Surfactant System
    We studied the effects of temperature and shear flow on the structures of alpha-gel bilayers and domains. The alpha-gel samples were prepared by a carboxylate-type gemini surfactant synthesized from oleic acid and a long-chain alcohol (1-tetradecanol) with water. The structural change as a function of temperature was investigated using small- and wide-angle X-ray scattering (SWAXS) measurements, spin-spin relaxation time (T-2) measurements, and optical microscopy observations. SWAXS measurements suggested that the decreased temperature yielded the alpha-gel phase from a lamellar liquid-crystal phase. We also found that the lamellar d-spacing drastically decreased at the phase transition temperature. The T-2 measurements suggested that two kinds of protons with different mobilities coexisted in amphiphiles consisting of lamellar bilayers. The abundance of the protons with low mobility increased with decreasing temperature. Optical microscopy results indicated that the size of the alpha-gel domains increased with decreasing temperature. We assumed that the increased abundance of the low-mobility protons, indicating low flexibility of lamellar bilayers, led to a decreased lamellar d-spacing and increased size of the alpha-gel domains. Shear-induced structural changes in the alpha-gel were also studied using simultaneous small-angle neutron scattering and rheological measurements. The alpha-gel can maintain bilayer structures even at high shear rates. We also found that the lamellar d-spacing was independent of the shear rate.
  • [期刊] Porous Silica-Pillared MXenes with Controllable Interlayer Distances for Long-Life Na-Ion Batteries
    MXenes are a recently discovered class of two-dimensional materials that have shown great potential as electrodes in electrochemical energy storage devices. Despite their promise in this area, MXenes can still suffer limitations in the form of restricted ion accessibility between the closely spaced multistacked MXene layers causing low capacities and poor cycle life. Pillaring, where a secondary species is inserted between layers, has been used to increase interlayer spacings in clays with great success but has had limited application in MXenes. We report a new amine-assisted pillaring methodology that successfully intercalates silica-based pillars between Ti3C2 layers. Using this technique, the interlayer spacing can be controlled with the choice of amine and calcination temperature, up to a maximum of 3.2 nm, the largest interlayer spacing reported for an MXene. Another effect of the pillaring is a dramatic increase in surface area, achieving BET surface areas of 235 m2 g(-1), a sixty-fold increase over the unpillared material and the highest reported for MXenes using an intercalation-based method. The intercalation mechanism was revealed by different characterization techniques, allowing the surface chemistry to be optimized for the pillaring process. The porous MXene was tested for Na-ion battery applications and showed superior capacity, rate capability and remarkable stability compared with those of the nonpillared materials, retaining 98.5% capacity between the 50th and 100th cycles. These results demonstrate the applicability and promise of pillaring techniques applied to MXenes providing a new approach to optimizing their properties for a range of applications, including energy storage, conversion, catalysis, and gas separations.
  • [期刊] Interfacial Instability of Emulsion Droplets Containing a Polymer and a Fatty Alcohol
    We investigated the interfacial instability of emulsion droplets via in situ measuring the oil/water interfacial tension (IFT) using the capillary suction method. The discrete phase of the oil-in-water emulsion contains a hydrophobic polymer (polystyrene, PS) and a fatty alcohol cosurfactant n-cetyl alcohol (CA) or n-octadecanol (OD), both of which were dissolved in an organic solvent (chloroform). The continuous phase is an aqueous solution of surfactant (sodium dodecyl sulfate, SDS). Upon removal of the organic solvent, the concentrations of CA and PS increase gradually, which induce a continual decrease of the IFT until the occurrence of interfacial instability. Micropipette tensiometry performed on an evaporating emulsion droplet reveals that interfacial instability is triggered when the IFT decreases close to similar to 0.17 mN/m. As a result, micron particles with wrinkled surfaces can be obtained after the complete removal of the organic solvent. The effect of the initial concentration and alkyl chain length of the cosurfactant on the interfacial instability and surface roughness of the formed particles was studied. This study provides theoretical guidance for the preparation of micrometer-sized polymer particles with diverse morphologies via the interfacial instability of emulsion droplets.
  • [期刊] Phase Behavior and Polymerization of the Ternary Polymerizable Cationic Gemini Surfactant/Fatty Alcohol/Water System
    We studied the phase behavior of a ternary polymerizable gemini surfactant (PC11-6-11)/1-undecanol/water system and stabilized these liquid crystalline structures through the polymerization of surfactants. The addition of 1-undecanol to a PC11-6-11/water system formed bicontinuous cubic (V-1) and reversed hexagonal (H-2) liquid crystal phases in addition to hexagonal (H-1) and lamellar (L-a) phases, which were also formed using the binary system of PC11-6-11/water. These new phases were formed because the fatty alcohol penetrated the palisade layer of the PC11-6-11 micelles. The polymerization of PC11-6-11 with a thermal initiator successfully preserved the L a and H-2 phases. Layered or honeycomb structures of these liquid crystals were clearly observed by transmission electron microscopy. The nanomaterials have potential applications as membranes for nano- or microfiltration and catalyst support materials.
  • [期刊] Droplets on Lubricant-Infused Surfaces: Combination of Constant Mean Curvature Interfaces with Neumann Triangle Boundary Conditions
    Superior mobility of droplets on lubricant-infused surfaces (LIS) has recently attracted significant attention for designing liquid-repellent surfaces. Unlike sessile droplets on flat surfaces wherein the contact line is easily visible in experiments, the contact line on LIS is masked by the lubricant meniscus, and special imaging techniques are required to visualize the hidden droplet-lubricant interface. Moreover, the overall shape deviates significantly from the spherical cap geometry even at very low droplet volumes. These difficulties necessitate the need to model interfaces in order to assess the effect of surface and fluid properties on LIS. In this work, we first numerically simulate the droplet shapes to show that at very small volumes, droplet-air and droplet-lubricant interfaces are constant mean curvature (CMC) interfaces. Moreover, we elucidate that these mean curvatures are related by the ratio of interfacial tensions of the droplet-air and the droplet-lubricant interfaces. These insights reduce the modeling of LIS interfacial profiles to a simplified geometric problem, which is solved using the parametric equations of CMC surfaces along with the angles of the Neumann triangle as the boundary conditions. Predicted profiles of the droplet-air interface as a spherical cap, the droplet-lubricant interface as a nodoid, and the lubricant-air interface as a catenoid/nodoid show good agreement with experimental results in the literature. Importantly, we for the first time provide a framework, which accurately predicts the true contact angle at the hidden solid contact line by just using the information of the top spherical cap portion visible in experiments.
  • [期刊] Nanoscale Work Function Contrast Induced by Decanethiol Self-Assembled Monolayers on Au(111)
    In this paper, we obtain maps of the spatial tunnel barrier variations in self-assembled monolayers of organosulfurs on Au(111). Maps down to the sub-nanometer scale are obtained by combining topographic scanning tunneling microscopy images with dI/dz spectroscopy. The square root of the tunnel barrier height is directly proportional to the local work function and the dI/dz signal. We use ratios of the tunnel barriers to study the work function contrast in various decanethiol phases: the lying-down striped beta phase, the dense standing-up phi phase, and the oxidized decanesulfonate lambda phase. We compare the induced work function variations too: the work function contrast induced by a lying-down striped phase in comparison to the modulation induced by the standing-up phi phase, as well as the oxidized lambda phase. By performing these comparisons, we can account for the similarities and differences in the effects of the mechanisms acting on the surface and extract valuable insights into molecular binding to the substrate. The pillow effect, governing the lowering of the work function due to lying-down molecular tails in the striped low density phases, seems to have quite a similar contribution as the surface dipole effect emerging in the dense standing-up decanethiol phases. The dI/dz spectroscopy map of the nonoxidized beta phase compared to the map of the oxidized lambda phase indicates that the strong binding of molecules to the substrate is no longer present in the latter.
  • [期刊] Modulation of Antimicrobial Peptide Conformation and Aggregation by Terminal Lipidation and Surfactants
    The function and properties of peptide-based materials depend not only on the amino acid sequence but also on the molecular conformations. In this paper, we chose a series of peptides G(m)(XXKK)(n)X-NH2 (m = 0, 3; n = 2, 3; X = I, L, and V) as the model molecules and studied the conformation regulation through N-terminus lipidation and their formulation with surfactants. The structural and morphological transition of peptide self-assemblies have also been investigated via transmission electron microscopy, atomic force microscopy, circular dichroism spectroscopy, and small-angle neutron scattering. With the terminal alkylation, the molecular conformation changed from random coil to beta-sheet or alpha-helix. The antimicrobial activities of alkylated peptide were different. C-16-G(3)(IIKK)(3)I-NH2 showed antimicrobial activity against Streptococcus mutans, while C-16-(IIKK)(2)I-NH2 and C-16-G(3)(IIKK)(2)I-NH2 did not kill the bacteria. The surfactant sodium dodecyl sulfonate could rapidly induce the self-assemblies of alkylated peptides (C-16-(IIKK)(2)I-NH2, C-16-G(3)(IIKK)(2)I-NH2, C-16-G(3)(VVKK)(2)V-NH2) from nanofibers to micelles, along with the conformation changing from beta-sheet to alpha-helix. The cationic surfactant hexadecyl trimethyl ammonium bromide made the lipopeptide nanofibers thinner, and nonionic surfactant polyoxyethylene (23) lauryl ether (C12EO23) induced the nanofibers much more intensively. Both the activity and the conformation of the alpha-helical peptide could be modulated by lipidation. Then, the self-assembled morphologies of alkylated peptides could also be further regulated with surfactants through hydrophobic, electrostatic, and hydrogen-bonding interactions. These results provided useful strategies to regulate the molecular conformations in peptide-based material functionalization.
  • [期刊] A Dendrimer-Based Dual Radiodense Element-Containing Nanoplatform for Targeted Enhanced Tumor Computed Tomography Imaging
    The exploration of original computed tomography (CT) imaging contrast agents with enhanced sensitivity and specificity is currently one of the major challenging tasks for precision medicine. Herein, we develop an innovative nanoprobe of dendrimer-stabilized gold nanoparticles (Au DSNs) linked with folic acid (FA) as a targeting ligand and diatrizoic acid (DTA) for specific enhanced tumor CT imaging. In current work, poly-(amidoamine) (PAMAM) dendrimers of generation 5 (G5) with amine termini were adopted to entrap Au NPs through a stepwise complexation/reduction method to achieve a higher Au loading than the conventional one-step complexation/reduction method. The prepared [(Au-0)(120)-G5.NH2] NPs were sequentially functionalized with diatrizoic acid (DTA), a typical CT contrast agent based on iodine(I), FA through a poly(ethylene glycol) (PEG) spacer, and carboxylated PEG monomethyl ether (mPEG-COOH), ended with complete acetylation of the leftover dendrimer amine termini. The generated Au DSNs-DTA-FA (Au core diameter = 5.9 nm) were thoroughly characterized. Our data reveal that the Au DSNs-DTA-FA containing Au and I dual radiodense elements are stable, display enhanced CT imaging performance, much higher than the single-radiodense elemental material solely based on Au or I, and possess a quite good cytocompatibility. With the demonstrated FA-rendered specific targeting, the developed Au DSNs-DTA-FA can be employed as a highly efficient nanoprobe for targeted enhanced CT imaging of cancer cells and a subcutaneous tumor model. Overall, the created Au DSNs-DTA-FA may be a powerful nanoprobe for specific enhanced CT imaging of various kinds of FA receptor-expressing tumors or biosystems.
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