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Halloysites as tubular alumosilicates are introduced as inexpensive natural nanoparticles to form and stabilize oil-water emulsions. This stabilized emulsion is shown to enable efficient interfacial catalytic reactions. Yield, selectivity, and product separation can be tremendously enhanced, e.g., for the hydroformylation reaction of dodecene to tridecanal. In perspective, this type of formulation may be used for oil spill dispersions. The key elements of the described formulations are clay nanotubes (halloysites) which are highly anisometric, can be filled by helper molecules, and are abundantly available in thousands of tons, making this technology scalable for industrial applications.
Janus droplets were prepared by vortex mixing of three non-mixable liquids, i.e., olive oil, silicone oil and water, in the presence of gold nanoparticles (AuNPs) in the aqueous phase and magnetite nanoparticles (MNPs) in the olive oil. The resulting Pickering emulsions were stabilized by a red-colored AuNP layer at the olive oil/water interface and MNPs at the oil/oil interface. The core–shell droplets can be stimulated by an external magnetic field. Surprisingly, an inner rotation of the silicon droplet is observed when MNPs are fixed at the inner silicon droplet interface. This is the first example of a controlled movement of the inner parts of complex double emulsions by magnetic manipulation via interfacially confined magnetic nanoparticles.
Janus droplets were prepared by vortex mixing of three non-mixable liquids, i.e., olive oil, silicone oil and water, in the presence of gold nanoparticles (AuNPs) in the aqueous phase and magnetite nanoparticles (MNPs) in the olive oil. The resulting Pickering emulsions were stabilized by a red-colored AuNP layer at the olive oil/water interface and MNPs at the oil/oil interface. The core–shell droplets can be stimulated by an external magnetic field. Surprisingly, an inner rotation of the silicon droplet is observed when MNPs are fixed at the inner silicon droplet interface. This is the first example of a controlled movement of the inner parts of complex double emulsions by magnetic manipulation via interfacially confined magnetic nanoparticles.
Polyplexes between a double-stranded Salmon DNA and hyperbranched poly(ethyleneimine) (PEI) as well as a maltosylated PEI-Mal were incorporated into a gelatin/chitosan hydrogel scaffold. Calorimetric experiments of the polyplexes show a decrease of the melting temperature in presence of PEI and a peak splitting in presence of PEI-Mal, which can be interpreted to a partial compaction of the DNA strands in presence of PEI-Mal. When the polyplexes are incorporated into a gelatin/chitosan scaffold in the swollen state, the DNA melting peaks at 90 and 93 degrees C, respectively, indicate in both cases the release of the DNA at the surface of the hydrogel scaffold in a more compact form. Specific interactions between the PEI-Mal shell and gelatin are responsible for the tuning of the release properties in presence of the maltose units in the hyperbranched PEI.
Negatively charged ultraflat gold nanotriangles (AuNTs) stabilized by the anionic surfactant dioctyl sodium sulfosuccinate (AOT) were reloaded with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC). Because of the spontaneous formation of a catanionic AOT micelle/BDAC bilayer onto the surface of the reloaded AuNTs, a reduction of Ag+ ions leads to the formation of spherical silver nanoparticles (AgNPs). With increasing concentration of AgNPs on the AuNTs, the localized surface plasmon resonance (LSPR) is shifted stepwise from 1300 to 800 nm. The tunable LSPR enables to shift the extinction maximum to the wavelength of the excitation laser of the Raman microscope at 785 nm. Surface-enhanced Raman scattering (SERS) experiments performed under resonance conditions show an SERS enhancement factor of the analyte molecule rhodamine RG6 of 5.1 X 10(5), which can be related to the silver hot spots at the periphery of the undulated gold nanoplatelets.
Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor.
Catanionic vesicles spontaneously formed by mixing the anionic surfactant bis(2-ethylhexyl)sulfosuccinate sodium salt with the cationic surfactant cetyltrimethylammonium bromide were used as a reducing medium to produce gold clusters, which are embedded and well-ordered into the template phase. The gold clusters can be used as seeds in the growth process that follows by adding ascorbic acid as a mild reducing component. When the ascorbic acid was added very slowly in an ice bath round-edged gold nanoflowers were produced. When the same experiments were performed at room temperature in the presence of Ag+ ions, sharp-edged nanoflowers could be synthesized. The mechanism of nanoparticle formation can be understood to be a non-diffusion-limited Ostwald ripening process of preordered gold nanoparticles embedded in catanionic vesicle fragments. Surface-enhanced Raman scattering experiments show an excellent enhancement factor of 1.7 . 10(5) for the nanoflowers deposited on a silicon wafer.
We report ultrasonically generated pH-responsive Pickering Janus emulsions of olive oil and silicone oil with controllable droplet size and engulfment. Chitosan was used as a pH-responsive emulsifier. The increase of pH from 2 to 6 leads to a transition from completely engulfed double emulsion droplets to dumbbell-shaped Janus droplets accompanied by a significant decrease of droplet diameter and a more homogeneous size distribution. The results can be elucidated by the conformational change of chitosan from a more extended form at pH 2 to a more flexible form at pH 4-5. Magnetic responsiveness to the emulsion was attributed by dispersing superparamagnetic nanoparticles (Fe3O4 with diameter of 13 +/- 2 nm) in the olive oil phase before preparing the Janus emulsion. Incorporation of magnetic nanoparticles leads to superior emulsion stability, drastically reduced droplet diameters, and opened the way to control movement and orientation of the Janus droplets according to an external magnetic field.
Self-assembling features of sodium dioctyl sulfosuccinate (AOT) molecules and micelle adsorption on gold Au (111) surfaces have been examined using molecular dynamics simulation. We argue that AOT micelles display a strong adsorption on gold surfaces resulting in distorted cylindrical micelles attached to the (111) facets. The well protected Au(111) facets decorated by a dense packed elongated ellipsoidal AOT layer hinder the diffusion of the reactant to the (111) facets and could result in the preferential growth of ultra-thin gold nanoplatelets.
Negatively charged ultrathin gold nanotriangles (AuNTs) were synthesized in a vesicular dioctyl sodium sulfosuccinate (AOT)/phospholipid-based template phase. These "naked" AuNTs with localized surface plasmon resonances in the NIR region at about 1300 nm and special photothermal properties are of particular interest for imaging and hyperthermia of cancerous tissues. For these kinds of applications the toxicity and the cellular uptake of the AuNTs is of outstanding importance. Therefore, this study focuses on the toxicity of "naked" AOT-stabilized AuNTs compared to polymer-coated AuNTs. Polymeric coating consisted of non-modified hyperbranched poly(ethyleneimine) (PEI), maltose-modified poly(ethyleneimine) (PEI-Mal) and heparin. The toxicological experiments were carried out with two different cell lines (embryonic kidney carcinoma cell line HEK293T and NK-cell leukemia cell line YTS). This study revealed that the heparin-coating of AuNTs improved biocompatibility by a factor of 50 when compared to naked AuNTs. Of note, the highest nontoxic concentration of the AuNTs coated with PEI and PEI-Mal is drastically decreased. Overall, this is mainly triggered by the different surface charges of polymeric coatings. Therefore, AuNTs coated with heparin were selected to carry out uptake studies. Their promising high biocompatibility and cellular uptake may open future studies in the field of biomedical applications. (C) 2018 Elsevier B.V. All rights reserved.
A sodium dioctyl sulfosuccinate (AOT)/benzyl hexadecyl dimethyl ammonium chloride (BDAC) mixed micelle self-organization and adsorption on gold Au(111) surfaces have been investigated using a molecular dynamics approach. The spherical AOT/BDAC mixed micelle is strongly adsorbed on the gold surface and is disoriented to a cylinder-like shape.
The aqueous self-assembly behavior of a series of poly(ethylene glycol)-poly(l-/d-lactide) block copolymers and corresponding stereocomplexes is examined by differential scanning calorimetry, dynamic light scattering, and transmission electron microscopy. Block copolymers assemble into spherical micelles and worm-like aggregates at room temperature, whereby the fraction of the latter seemingly increases with decreasing lactide weight fraction or hydrophobicity. The formation of the worm-like aggregates arises from the crystallization of the polylactide by which the spherical micelles become colloidally unstable and fuse epitaxically with other micelles. The self-assembly behavior of the stereocomplex aggregates is found to be different from that of the block copolymers, resulting in rather irregular-shaped clusters of spherical micelles and pearl-necklace-like structures.
A molecular dynamics study was done to reveal the adsorption properties of sodium dioctyl sulfosuccinate (AOT) bilayers on gold Au(111) surfaces. Examining the rotational mobility of AOT molecules, we track that the correlation time of AOT molecules on the adsorbed layer is much higher. The data estimating the diffusive motion of AOT molecule show a substantially lower rate of diffusion (similar to 10(-10) cm(2)/s) in the adsorbed layers in comparison to other ones. The results show that an adsorbed layer is more rigid, whereas the outer layers undergo considerable lateral and vertical fluctuations.
In the present work, we study the shear-induced transformation of polymer-rich lamellar phases into vesicles. The evolution of vesicle size is studied by different scattering techniques, rheology, and microscopy methods. The lamellar phase found in the system D2O/o-xylene/Pluronic PE9400/C(8)TAB can be fully transformed to multilamellar vesicles (MLVs) by applying shear. The size of the MLVs is proportional to the inverse square root of the shear rate. Hence, the polymer based quaternary system behaves similar to lamellar phases based on small surfactant molecules. Additionally, we found a growth effect leading to a size increase of the vesicles after shearing was stopped.
SpineMan is designed as a prototype of a soft robotic manipulator that is constructed of alternating hard and soft segments similar to the human spine. Implementing such soft segments allows to surpass the rigidity of conventional robots and ensures safer workspaces where humans and machines can work side by side with less stringent safety restrictions. Therefore, we used a hydrogel as viscoelastic material consisting of poly(vinyl alcohol) and borax. The mechanical properties of the hydrogel were tailored by embedding silica particles of various particles sizes as well as in different mass fractions. Increased mass contents as well as larger particle sizes led to strongly enhanced rigidity with a more than doubled storage modulus of the composite compared to the pure hydrogel. Furthermore, specific functionalities were induced by the incorporation of superparamagnetic Fe3O4 nanoparticles that can in principle be used for sensing robotic motion and detecting malfunctions. Therefore, we precisely adjusted the saturation magnetization of the soft segments using defined mass contents of the nanoparticles. To ensure long-time shape stability and prevention of atmospheric influences on the prepared composites, a silicone skin of specific shore hardness was used. The composites and the soft segments were characterized by oscillation measurements, cryo-SEM, bending tests and SQUID measurements, which give insights into the properties in the passive and in the moving state of SpineMan. The utilization of tailored composites led to highly flexible, reinforced and functional soft segments, which ensure stability, easy movability by springs of the shape memory alloy nitinol and prevention of total failure.
Nanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4′-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by one-dimensional heat transport.
Pickering emulsions with two types of nanoparticles, i.e., superparamagnetic magnetite nanoparticles dispersed in n-hexane and gold nanoparticles dispersed in water, were formed by rigorous mixing in presence of surface active polymeric surfactants. Monodisperse magnetite nanoparticles with a mean particle size of 4 nm were obtained by a microwave-assisted synthesis in n-hexane in presence of oleic acid, and gold nanoparticles were produced in aqueous solution in presence of the hyperbranched poly(ethyleneimine) (PEI) or sodium citrate as reducing and stabilizing agent. After mixing the prepared nanoparticle dispersions in presence of the Pluronics an intermediate gel-like phase is formed. The Pickering emulsion droplets in the intermediate phase are stabilized by both types of nanoparticles, as to be seen by cryo-SEM micrographs. After separating, solvent evaporation and redispersion in water highly ordered Pluronic-stabilized superparamagnetic magnetite nanoparticle aggregates with embedded gold nanoparticles can be obtained.
New cryogels for selective dye removal from aqueous solution were prepared by free radical polymerization from the highly water-soluble crosslinker N,N,N’,N’-tetramethyl-N,N’-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The resulting white and opaque cryogels have micrometer sized pores with a smaller substructure. They adsorb methyl orange (MO) but not methylene blue (MB) from aqueous solution. Mixtures of MO and MB can be separated through selective adsorption of the MO to the cryogels while the MB remains in solution. The resulting cryogels are thus candidates for the removal of hazardous organic substances, as exemplified by MO and MB, from water. Clearly, it is possible that the cryogels are also potentially interesting for removal of other compounds such as pharmaceuticals or pesticides, but this must be investigated further.
New cryogels for selective dye removal from aqueous solution were prepared by free radical polymerization from the highly water-soluble crosslinker N,N,N’,N’-tetramethyl-N,N’-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The resulting white and opaque cryogels have micrometer sized pores with a smaller substructure. They adsorb methyl orange (MO) but not methylene blue (MB) from aqueous solution. Mixtures of MO and MB can be separated through selective adsorption of the MO to the cryogels while the MB remains in solution. The resulting cryogels are thus candidates for the removal of hazardous organic substances, as exemplified by MO and MB, from water. Clearly, it is possible that the cryogels are also potentially interesting for removal of other compounds such as pharmaceuticals or pesticides, but this must be investigated further.