Nicolas Vogel

In this study, we systematically analyze the surface tension and Hansen solubility parameters (HSPs) of imidazolium-based ionic liquids (ILs) with different anions ([NTf2]−, [PF6]−, [I]−, and [Br]−). These anions are combined with the classical 1-alkyl-3-methyl-substituted imidazolium cations ([CnC1Im]+) and a group of oligoether-functionalized imidazolium cations ([(mPEGn)2Im]+) based on methylated polyethylene glycol (mPEGn). In detail, the influences of the length of the alkyl- and the mPEGn-chain, the anion size, and the water content are investigated experimentally. For [CnC1Im]+-based ILs, the surface tension decreases with increasing alkyl chain length in all cases, but the magnitude of this decrease depends on the size of the anion ([NTf2]− < [PF6]− < [Br]− ≤ [I]−). Molecular dynamics (MD) simulations on [CnC1Im]+-based ILs indicate that these differences are caused by the interplay of charged and …

Nanostructured materials that mimic structural coloration in nature can be synthetically created by colloidal self‐assembly. To maximize optical effects, the natural world integrates melanin as a broadband absorber to remove incoherently scattered light. Polydopamine (PDA) is used as a synthetic analog of natural melanin to systematically investigate the influence of absorber quantity and distribution on color saturation in colloidal photonic crystals. The absorbing PDA is integrated into two distinct ways: homogenous colloidal crystals are produced from core–shell particles with incrementally increasing polydopamine shells, and heterogeneous colloidal crystals are formed by co‐assembly of varying ratios of polystyrene (PS) and absorbing PS@PDA particles. The chromaticity is quantified by converting the measured spectra to reconstructed colors in the L*a*b* color sphere to identify structures with optimal color …

Unraveling the two-dimensional (2D) structural ordering of colloidal particles assembled at a flat surface is essential for understanding and optimizing their physical properties. So far, grazing-incidence small-angle X-ray scattering (GISAXS) has been widely used to determine crystallographic information on 2D self-assembled structures of nanosize objects. However, solving the structure of 2D lattices consisting of micrometer (μm)-sized objects still remains a challenge using scattering methods. Here, a model 2D SCALMS (supported catalytically active liquid metal solution) template is fabricated from μm-sized polystyrene (PS) spheres that form a monolayer on top of the flat solid support. GISAXS patterns of the sample were collected for rotation angles around its surface normal in steps of 3°. For every rotation angle, different Bragg-type interference maxima along the out-of-plane (qz) direction were observed. On …

In this study, we show the design and manufacturing of microfluidic deterministic lateral displacement (DLD) devices for sub-micrometer particle separation. For that purpose, devices with pillar gaps of 4 µm and a periodicity of 50 were designed. After photolithographic manufacturing of SU-8 masters with different heights (15 and 30 µm) and vertical sidewalls for soft-lithographic replication with polydimethylsiloxane (PDMS) the influence of flow rate on the separation efficiency of 0.45 and 0.97 µm particles was investigated. The 15 µm devices were operated at 0.125 and 0.5 µl/min sample flow rate and the 30 µm devices at 0.5 and 2.0 µl/min, respectively. Excellent separation efficiencies were observed for both device heights at the lower sample flow rates, while separation efficiencies decreased at the respective higher sample flow rates. The decrease in separation efficiency was attributed to deformation of the soft …

Continuous gradients in self-assembled materials can provide functionality exceeding that of the homogenous case. In article number 2208745, Markus Retsch and co-workers present a synthesis method that provides gradient size distributions via a controlled extraction emulsion process (CrEEP). The high degree of control allows the fabrication of a continuous-gradient photonic glass with enhanced broadband reflectance.

Molecular chirality plays fundamental roles in biology. The chiral response of a molecule occurs at a specific spectral position, determined by its molecular structure. This fingerprint can be transferred to other spectral regions via the interaction with localized surface plasmon resonances of gold nanoparticles. Here, we demonstrate that molecular chirality transfer occurs also for plasmonic lattice modes, providing a very effective and tunable means to control chirality. We use colloidal self-assembly to fabricate non-close packed, periodic arrays of achiral gold nanoparticles, which are embedded in a polymer film containing chiral molecules. In the presence of the chiral molecules, the surface lattice resonances (SLRs) become optically active, i.e., showing handedness-dependent excitation. Numerical simulations with varying lattice parameters show circular dichroism peaks shifting along with the spectral positions of …

A novel strategy for manufacturing of the main insulation of high‐voltage rotating machines is presented. The developed process is based on established electrostatic powder coating equipment. Using complete automation enables the precise and reproducible application of homogeneous powder coating layers. Individual layers can be stacked by process repetitions to achieve a desired layer thickness. This coating strategy alters the particle deposition process by introducing additional capillary bridges that significantly increase powder adhesion. A systematic parameter study is performed to provide process–structure relations connecting various process parameters with the resultant coating thickness and homogeneity. The parameters of the developed coating process are iteratively improved to maximize coating homogeneity and minimize defect density, the most critical parameters in high‐voltage insulation …

Liquid‐infused surfaces exhibit remarkable repellency properties toward water, oils, and complex fluids and are widely applied to maintain clean, operational, and high‐performing surfaces in various fields, from the biomedical sector to marine infrastructure. Polydopamine (PDA) forms an ideal base layer for the development of such coatings as it adheres to virtually any substrate and can be chemically modified via amino‐containing molecules to adjust the surface properties. Here, strategies are explored to increase the mechanical stability of such coatings by i) incorporating imidazole during film formation to increase crosslinking, and ii) formation of a composite consisting of the organic PDA and an inorganic siliceous porous coating by infiltration of a preformed porous silica layer with PDA. Both strategies exhibit improved resistance to tangential shear assessed by a sandpaper abrasion test and to dynamic …