Thermosensitive hollow Janus dumbbells

Thermosensitive hollow Janus dumbbells, consisting of two partially fused hollow poly (N-isopropylacrylamide) (PNIPAM) spheres, were prepared using dumbbell-shaped microgels as templates. One sphere has a shell completely made of PNIPAM while the other one has a hybrid shell, which is a poly(styrene-co-3-(trimethoxysilyl)propyl methacrylate) layer covered by PNIPAM. The morphology of hollow Janus dumbbells is fully characterized by cryo- and transmission electron microscopy, scanning force microscopy, and dynamic light scattering. Transmission electron microscopy demonstrates that the particles have a very narrow size distribution. The analysis by depolarized dynamic light scattering showed that the hollow Janus dumbbells exhibit a thermosensitive behavior comparable to the dumbbell-shaped microgels before the removal of the core.     

The Effect of Water on the 2-Propanol Oxidation Activity of Co-Substituted LaFe1−xCoxO3 Perovskites

Perovskites are interesting oxidation catalysts due to their chemical flexibility enabling the tuning of several properties. In this work, we synthesized LaFe_1−xCo_xO₃ catalysts by co-precipitation and thermal decomposition, characterized them thoroughly and studied their 2-propanol oxidation activity under dry and wet conditions to bridge the knowledge gap between gas and liquid phase reactions. Transient tests showed a highly active, unstable low-temperature (LT) reaction channel in conversion profiles and a stable, less-active high-temperature (HT) channel. Cobalt incorporation had a positive effect on the activity. The effect of water was negative on the LT channel, whereas the HT channel activity was boosted for x>0.15. The boost may originate from a slower deactivation rate of the Co³⁺ sites under wet conditions and a higher amount of hydroxide species on the surface comparing wet to dry feeds. Water addition resulted in a slower deactivation for Co-rich catalysts and higher activity in the HT channel state.     

Surface organization and cooperativity during nonspecific protein adsorption events

Despite many experimental studies on cooperative effects during protein adsorption events, this phenomenon is still poorly characterized and subject of much controversy. In this study, we address the topic of cooperativity using two distinct experimental approaches, namely, kinetic analysis and surface imaging, both based on supercritical angle fluorescence (SAF) microscopy. Several model systems comprising the two proteins BSA and fibrinogen, two different ionic strength conditions and varying pH environments were investigated. The combination of the experimental information obtained from kinetic analysis and from real-time in situ scan images unravel a clear correlation between cooperative adsorption and a heterogeneous protein layer build-up. We propose a mechanistic model of protein adsorption based on an overlap of classical Langmuir-type adsorption on unoccupied surface areas and an additional cooperative adsorption pathway near preadsorbed proteins which is consistent with the experimental observations. Moreover, the growth of two-dimensional surface clusters as an often assumed element of cooperativity could be excluded for the studied systems. The model includes the often observed phenomenon that the adsorption rate decelerates abruptly above a certain coverage limit. Furthermore, the observed evolution of the heterogeneous protein distribution on the surface is in good agreement with the proposed model.     

Towards nanotubular structures with large voids: dynamic heteroleptic oligophenanthroline metallonanoscaffolds and their solution-state properties

The assembly of a rigid macrocycle with two exotopic phenanthroline binding sites in combination with linear bis- or trisphenanthrolines and copper(I) ions is used to generate nanoscale double and triple deckers, the latter showing a tubular structure. With supramolecular chemistry expanding to dynamic, large cavity, nanoscale structures, it becomes increasingly important to use robust assembly protocols as well as reliable characterization techniques. To fully elucidate and to describe the dynamic nature of metallonanoscaffolds with large voids, we applied a battery of both direct and indirect solution-state characterization methods. These methods along with the conventional direct methods provide a very useful tool for characterizing tubular nanoscaffold aggregates.     

Formation of intra-island grain boundaries in pentacene monolayers

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.     

Anisotropic nanoparticles of precise microstructure polyolefins

Nanoparticles of precisely branched polyethylenes possess a distinct oblate shape resulting from a crystalline lamella in the particle as revealed by SAXS and TEM, and display controllable and well-behaved thermal behaviour.