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Journal of colloid and interface science
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Item-typ:Veröffentlichung, Assessment of nanoparticle immersion depth at liquid interfaces from chemically equivalent macroscopic surfaces(Elsevier Science, 2022-04); ; ; ; Hypothesis: We test whether the wettability of nanoparticles (NPs) straddling at an air/water surface or oil/water interface can be extrapolated from sessile drop-derived macroscopic contact angles (mCAs) on planar substrates, assuming that both the nanoparticles and the macroscopic substrates are chemically equivalent and feature the same electrokinetic potential. Experiments: Pure silica (SiO2) and amino-terminated silica (APTES-SiO2) NPs are compared to macroscopic surfaces with extremely low roughness (root mean square [RMS] roughness ≤ 2 nm) or a roughness determined by a close-packed layer of NPs (RMS roughness ∼ 35 nm). Equivalence of the surface chemistry is assessed by comparing the electrokinetic potentials of the NPs via electrophoretic light scattering and of the macroscopic substrates via streaming current analysis. The wettability of the macroscopic substrates is obtained from advancing (ACAs) and receding contact angles (RCAs) and in situ synchrotron X-ray reflectivity (XRR) provided by the NP wettability at the liquid interfaces. Findings: Generally, the RCA on smooth surfaces provides a good estimate of NP wetting properties. However, mCAs alone cannot predict adsorption barriers that prevent NP segregation to the interface, as is the case with the pure SiO2 nanoparticles. This strategy greatly facilitates assessing the wetting properties of NPs for applications such as emulsion formulation, flotation, or water remediation.Wissenschaftlicher ArtikelBand:61164 69 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A new silicon oxycarbide based gas diffusion layer for zinc-air batteries(Elsevier {BV}, 2020-06-05); ; ; ; Rational material designs play a vital role in the gas diffusion layer (GDL) by increasing the oxygen diffusion rate and, consequently, facilitating a longer cycle life for metal-air batteries. In this work, a new porous conductive ceramic membrane has been developed as a cathodic GDL for zinc-air battery (ZAB). The bilayered structure with a thickness of 390 μm and an open porosity of 55% is derived from a preceramic precursor with the help of the freeze tape casting technique. The hydrophobic behaviour of the GDL is proved by the water contact angle of 137.5° after the coating of polytetrafluoroethylene (PTFE). The electrical conductivity of 5.59 * 10-3 S/cm is reached using graphite and MWCNT as filler materials. Tested in a ZAB system, the as-prepared GDL coated with commercial Pt-Ru/C catalyst shows an excellent cycle life over 200 cycles and complete discharge over 48 h by consuming oxygen from the atmosphere, which is comparable to commercial electrodes. The as-prepared electrode exhibits excellent ZAB performance due to the symmetric sponge-like structure, which facilitates the oxygen exchange rate and offers a short path for the oxygen ion/-electron kinetics. Thus, this work highlights the importance of a simple manufacturing process that significantly influences advanced ZAB enhancement.Wissenschaftlicher ArtikelBand:577195 167 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Electrostatic assembly of zwitterionic and amphiphilic supraparticlesWe demonstrate the electrostatic assembly of oppositely charged silica particles into an ensemble of well-defined core-satellite supraparticles, which are a type of patchy particle. To achieve controlled heteroaggregation, we used oppositely charged silica particles with different sizes ranging from 5nm to 150nm at several concentrations. The assembly works best with larger particles, resulting in a fairly low polydispersity and a low amount of bridging between the individual clusters. Using smaller particles produces high polydispersity, large clusters and uncontrolled aggregation and bridging. Furthermore, even with controlled aggregation into well-defined clusters in the case of bigger particles, we observe an uneven covering of the central particles with around 1-6 satellite particles adsorbed to the central particle. This behavior is not predicted by simple pairwise DLVO potentials which would anticipate an even spacing of the satellite particles on the core. We explain these observations by taking into account the interactions of the adsorbing particles within the ionic cloud of the central particle. We hypothesize that when the adsorbing satellite particles are small compared to the diameter of the ion cloud of the core particle, they aggregate within the ion cloud and therefore do not create a well-defined monolayer on the surface of the core particle, instead forming small agglomerates during adsorption. Finally, both the assembled zwitterionic clusters and clusters that were partially hydrophobized were tested for their capabilities as Pickering emulsifiers. The zwitterionic clusters showed a strongly increased surface activity compared to the individual particles, while the hydrophobized particles changed the emulsion type from w/o to o/w. Interfacial dilatational rheological tests supported the observations from the emulsion tests. With this, we demonstrate that a relatively unordered ensemble of supraparticles is able to show well-defined functionality at a higher hierarchical level as Pickering emulsifiers.Wissenschaftlicher ArtikelBand:501109 85 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Coatings of active and heat-resistant cobalt-aluminium xerogel catalysts(Elsevier, 2016-05-28); ; ; ; The application of catalytically coated metallic foams in catalytic processes has a high potential for exothermic catalytic reactions such as CO2 methanation or Fischer-Tropsch synthesis due to good heat conductivity, improved turbulent flow properties and high catalyst efficiencies. But the preparation of homogenous catalyst coats without pore blocking is challenging with conventional wash coating techniques. Here, we report on a stable and additive free colloidal CoAlOOH suspension (sol) for the preparation of catalytically active Co/Al2O3 xerogel catalysts and coatings. Powders with 18wt% Co3O4 prepared from this additive free synthesis route show a catalytic activity in Fischer-Tropsch synthesis and CO2 methanation which is similar to a catalyst prepared by incipient wetness impregnation (IWI) after activating the material under flowing hydrogen at 430°C. Yet, the xerogel catalyst exhibits a much higher thermal stability as compared to the IWI catalyst, as demonstrated in catalytic tests after different heat agings between 430°C and 580°C. It was also found that the addition of polyethylene glycol (PEG) to the sol influences the catalytic properties of the formed xerogels negatively. Only non-reducible cobalt spinels were formed from a CoAlOOH sol with 20wt% PEG. Metallic foams with pores sizes between 450 and 1200μm were coated with the additive free CoAlOOH sol, which resulted in homogenous xerogel layers. First catalytic tests of the coated metal foams (1200μm) showed good performance in CO2 methanation.Wissenschaftlicher ArtikelBand:47784 117