Escape-Rate Formalism, Decay to Steady States, and Divergences in the Entropy-Production Rate

According to thermodynamics the irreversible entropy production of diffusive relaxation processes diverges at the boundary to the vacuum, i.e., to a state of vanishing particle density. By means of a multibaker map we point out that this divergence is not present in the spatially discrete dynamics, which brings forth the evolution equations of irreversible thermodynamics in the continuum limit. In addition, we show that the irreversible entropy production of relaxation towards a nonempty steady state is proportional to the decay rate of the thermodynamic system subjected to absorbing boundary conditions. This generalizes results of the escape rate formalism.     

Toward the characterization of peptidoglycan structure and protein-peptidoglycan interactions by solid-state NMR spectroscopy

Solid-state NMR spectroscopy is applied to intact peptidoglycan sacculi of the Gram-negative bacterium Escherichia coli. High-quality solid-state NMR spectra allow atom-resolved investigation of the peptidoglycan structure and dynamics as well as the study of protein-peptidoglycan interactions.     

Towards a Cradle-to-Cradle Polyolefin Lifecycle

Achieving efficient chemical depolymerization of waste polyolefins to monomers remains an unsolved challenge, while it could be an effective means to avoid further waste accumulation in the environment and generate economic benefits. In a recent publication by Conk et al., polyethylene (PE) is converted to propylene, the second most used monomer in the polymer industry. The conversion is achieved via a tandem catalysis approach in which partially unsaturated PE chains react with ethylene to generate propylene with yields as high as 87 %. The study is a first proof of concept showcasing a selective chemical depolymerization of PE to a monomer. Future research is expected to focus on the catalyst optimization, process design, and compatibility with contaminated and multi-polymer waste streams.     

Microfluidic flow rate detection based on integrated optical fiber cantilever

We demonstrate an integrated microfluidic flow sensor with ultra-wide dynamic range, suitable for high throughput applications such as flow cytometry and particle sorting/counting. A fiber-tip cantilever transduces flow rates to optical signal readout, and we demonstrate a dynamic range from 0 to 1500 microL min(-1) for operation in water. Fiber-optic sensor alignment is guided by preformed microfluidic channels, and the dynamic range can be adjusted in a one-step chemical etch. An overall non-linear response is attributed to the far-field angular distribution of single-mode fiber output.     

Assessing a novel microfluidic interface for shotgun proteome analyses

Microfluidic interfaces coupled to ESI mass spectrometers hold great potential for proteomics as they have been shown to augment the overall sensitivity of measurements and require only a minimum of operator manipulations as compared to conventional nano-LC interfaces. Here, we evaluated a new type of HPLC-Chips holding larger enrichment columns (thus an increased sample loading capacity) for gel-free proteome studies. A tryptic digest of a human T-cell proteome was fractionated by strong cation exchange chromatography and selected fractions were analyzed by MS/MS on an IT mass spectrometer using both the new HPLC-Chip as well as a conventional nano-LC-MS/MS interface. Our results indicate that the HPLC-Chip is capable of handling very complex peptide mixtures and, in fact, leads to the identification of more peptides and proteins as compared to when a conventional interface was used. The HPLC-Chip preferentially produced doubly charged tryptic peptides. We further show that MS/MS spectra of doubly charged tryptic peptide ions are more readily identified by MASCOT as compared to those from triply charged precursors and thus argue that besides the improved chromatographic conditions provided by the HPLC-Chip, its peptide charging profile might be a secondary factor leading to an increased proteome coverage.     

Electronic Properties of Interfaces between PCPDTBT and Prototypical Electrodes Studied by Photoemission Spectroscopy

We report on the electronic structure of poly[2,6‐(4,4‐bis‐ (2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothiadiazole)] (PCPDTBT), a promising low‐band‐gap donor material for efficient bulk heterojunction organic solar cells. Electronic properties of interfaces formed between PCPDTBT and prototypical electrodes [Au, indium‐tin‐oxide and poly(ethylene‐dioxythiophene): poly(styrenesulfonate)], obtained from X‐ray photoemission spectroscopy and ultraviolet photoemission spectroscopy, are evaluated. The formation of interface dipoles is observed, and their consequences for device performance are discussed. For the system PCPDTBT/Au chemical interactions occur, which may affect in particular the charge extraction at the corresponding interface.     

Pattern formation in phase separating binary mixtures

We experimentally investigate the interplay of thermodynamics with hydrodynamics during phase separation of (quasi-) binary mixtures. Well defined patterns emerge while slowly crossing the cloud point curve. Depending on the material parameters of the experimental system, two distinct scenarios are observed. In quasi-binary mixtures of methanol-hexane patterns appear before macroscopic phase separation sets in. In course of time the patterns turn faint while the overall turbidity of the sample increases until the mixtures become completely turbid. We attribute this pattern formation to a latent heat induced instability resembling a Rayleigh-Bénard instability. This is confirmed by calorimetric data and an estimate of its Rayleigh number. Mixtures of C(4)E(1)-water doped with decane phase separate under heating. After passing the cloud point curve these mixtures first become homogenously turbid. While clearing up, pattern formation is observed. We attribute this type of pattern formation to an interfacial tension induced Bénard-Marangoni instability. The occurrence of the two scenarios is supported by the relevant dimensionless numbers.     

Wetting on the microscale: shape of a liquid drop on a microstructured surface at different length scales

Describing wetting of a liquid on a rough or structured surface is a challenge because of the wide range of involved length scales. Nano- and micrometer-sized textures cause pinning of the contact line, reflected in a hysteresis of the contact angle. To investigate contact angles at different length scales, we imaged water drops on arrays of 5 μm high poly(dimethylsiloxane) micropillars. The drops were imaged by laser scanning confocal microscopy (LSCM), which allowed us to quantitatively analyze the local and large-scale drop profile simultaneously. Deviations of the shape of drops from a sphere decay at two different length scales. Close to the pillars, the amplitude of deviations decays exponentially within 1-2 μm. The drop profile approached a sphere at a length scale 1 order of magnitude larger than the pillars' height. The height and position dependence of the contact angles can be understood from the interplay of pinning of the contact line, the principal curvatures set by the topography of the substrate, and the minimization of the air-water interfaces.