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Tarnawski R.,University of Duisburg - Essen | Ulbricht M.,University of Duisburg - Essen | Ulbricht M.,Center for Nanointegration Duisburg Essen
Colloids and Surfaces A: Physicochemical and Engineering Aspects

The direct synthesis of water-soluble gold nanoparticles with a mixed shell of two different thiols, 1-mercaptoundec-11-yl-hexa(ethylene glycol) (EG6) and dodecanethiol (C12), and their characterization are reported. Data from IR spectroscopy and contact angle (CA) measurements as well as the solubility of the nanoparticles in water support that the composition of the shell is in the range of the thiol ratio used for synthesis (EG6:C12 = 72:28). Results of transmission electron microscopy and atomic force microscopy (AFM) for deposited particles as well as the UV-vis spectrum in solution are in line with a size of ≤10. nm. Self-assembled monolayers (SAMs) as model surfaces were prepared from mixtures of EG6 and C12 on planar gold films. Polystyrene (PSt) spin-coated films on silicon wafers and on gold-coated surface plasmon resonance (SPR) sensor disks were used as substrates for surface functionalization via adsorption/self-assembly of a polystyrene poly(ethylene glycol) diblock copolymer (PSt- b-PEG) from aqueous solutions. CA and AFM results revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surface as a function of PSt- b-PEG concentration used for the modification. The adsorption of myoglobin and the novel gold nanoparticles to the PSt- b-PEGylated surfaces was analyzed by SPR. A control of adsorbed amounts by the degree of surface PEGylation, i.e. a reduction by up to 55% for the highest degree of modification, could be confirmed for both kinds of colloids. Adsorption of the novel gold nanoparticles to the mixed SAM surfaces as analyzed by SPR showed an even stronger dependency of surface composition. All experiments demonstrate that amphiphilic, water-soluble gold-based nanoparticles can be used as model colloids for the investigation of interactions with polymer surfaces of varied structure and architecture, and that they could be further developed for analytical or biological applications. © 2010 Elsevier B.V. Source

Mathieu M.,Center for Nanointegration Duisburg Essen | Hartmann N.,University of Duisburg - Essen
New Journal of Physics

In recent years, nonlinear processing with continuous-wave lasers has been demonstrated to be a facile means of rapid nanopatterning of organic monolayers down to the sub-100 nm range. In this study, we report on laser patterning of thiol-based organic monolayers with sub-wavelength resolution. Au-coated silicon substrates are functionalized with 1-hexadecanethiol. Irradiation with a focused beam of an Ar+ laser operating at λ = 514 nm allows one to locally remove the monolayer. Subsequently, the patterns are transferred into the Au film via selective etching in a ferri-/ferrocyanide solution. Despite a 1/e2 spot diameter of about 2.8 μm, structures with lateral dimensions down to 250 nm are fabricated. The underlying nonlinear dependence of the patterning process on laser intensity is traced back to the interplay between the laser-induced transient local temperature rise and the thermally activated desorption of the thiol molecules. A simple thermokinetic analysis of the data allows us to determine the effective kinetic parameters. These results complement our previous work on photothermal laser patterning of ultrathin organic coatings, such as silane-based organic monolayers, organo/silicon interfaces and supported membranes. A general introduction to nonlinear laser processing of organic monolayers is presented. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Kumar M.,Center for Nanointegration Duisburg Essen | Ulbricht M.,University of Duisburg - Essen
Separation and Purification Technology

Low fouling negatively charged hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of poly(arylene ether sulfone) (PAES) block copolymer and the sulfonated copolymer (S-PAES) in combination with different fractions of sulfonic acid functionalized multiwalled carbon nanotubes (MWCNT-SO3H) by non-solvent induced phase separation method. Porous hybrid membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Results confirmed that the fabricated membranes were hydrophilic and negatively charged in the studied pH range 3-10. The water permeabilities and increased protein fouling resistances of the membranes were dependent on the fraction of MWCNT-SO3H in the membranes. The protein transmission as function of pH value and fraction of MWCNT-SO3H was studied for two model proteins (bovine serum albumin and myoglobin) and found to be controlled by size exclusion and the content of MWCNT-SO3H. The highest transmission of proteins at their isoelectric points was obtained for the membrane containing 2 wt% of MWCNT-SO3H relative to total membrane polymer. The selectivity of the hybrid membranes for the separation of the binary protein mixture could be systematically increased by increasing surface charge density by increasing fraction of MWCNT-SO3H. Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome and performance be tuned by a small fraction of a functional additive. © 2014 Elsevier B.V. All rights reserved. Source

Schulz S.,University of Duisburg - Essen | Schulz S.,Center for Nanointegration Duisburg Essen
Coordination Chemistry Reviews

Our understanding on the nature of weak intermolecular metal-metal interactions as well as of multiple bonding in group 15/16 chemistry, in particular of compounds containing the heaviest elements of both groups - Sb, Bi, Se, and Te - is still scarce. These types of interactions are particularly important for the chemical and physical properties of such main group element compounds. For instance, the formation and disruption of weak intermolecular metal-metal interactions are the origin of the so-called thermochroism. The structural characterization of compounds containing sterically less demanding organic substituents is therefore of particular interest, since the capability of small substituents to kinetically stabilize the respective metal centers - and hence to suppress intermolecular interactions - is expected to be rather less pronounced. We will herein summarize the most recent results reported for the synthesis and structural characterization of group 15/16 compounds containing a direct (polar-covalent) element-element bond including compounds containing a terminal, formally double bond. In addition, the capability of selected compounds to serve as single-source precursor for the synthesis of the corresponding nanomaterials, in particular Sb2Te3 and Bi2Te3, by using wet chemical methods as well as gas phase approaches such as metal organic chemical vapor deposition (MOCVD) processes will be demonstrated. © 2014 Elsevier B.V. Source

Chen S.-C.,University of Minnesota | Wang J.,ETH Zurich | Wang J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Fissan H.,Institute of Energy and Environmental Technology E.V. IUTA | And 2 more authors.
Atmospheric Environment

Nuclepore filter collection with subsequent electron microscopy analysis for nanoparticles was carried out to examine the feasibility of the method to assess the nanoparticle exposure. The number distribution of nanoparticles collected on the filter surface was counted visually and converted to the distribution in the air using existing filtration models for Nuclepore filters. To search for a proper model, this paper studied the overall penetrations of three different nanoparticles (PSL, Ag and NaCl), covering a wide range of particle sizes (20-800nm) and densities (1.05-10.5gcm-3), through Nuclepore filters with two different pore diameters (1 and 3μm) and different face velocities (2-15cms-1). The data were compared with existing particle deposition models and modified models proposed by this study, which delivered different results because of different deposition processes considered. It was found that a parameter associated with flow condition and filter geometry (density of fluid medium, particle density, filtration face velocity, filter porosity and pore diameter) should be taken into account to verify the applicability of the models. The data of the overall penetration were in very good agreement with the properly applied models. A good agreement of filter surface collection between the validated model and the SEM analysis was obtained, indicating a correct nanoparticle number distribution in the air can be converted from the Nuclepore filter surface collection and this method can be applied for nanoparticle exposure assessment. © 2013 Elsevier Ltd. Source

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