Hierarchical Layer Engineering Using Supramolecular Double‐Comb Diblock Copolymers

The formation of unusual multilayered parallel lamellae‐in‐lamellae in symmetric supramolecular double‐comb diblock copolymers is presented. While keeping the concentration of surfactant fixed, the number of internal layers was found to increase with molecular weight M up to 34 for the largest block copolymer. The number of internal structures n was established to scale as M^0.67 and therefore enables easy design of such structures with great precision.     

Cellulose nanocrystal submonolayers by spin coating

Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).     

Surface modification and characterization of thermoplastic polyurethane

This work reports the modification of thermoplastic polyurethanes (TPUs) in order to enlarge their application range, for example, as biomaterials by increasing its hydrophilicity.A TPU was successfully modified by using three different strategies: ultra-violet irradiation (UV), gamma irradiation (GI) and interfacial modification (IM). The results suggested the possibility of modifying the polyurethane-based surface either with poly(ethylene glycol) (PEG) or hydroxylethyl methacrylate (HEMA) or hexamethylene diamine (HMD) or chitosan (CT) by using any of these methods. The properties of the grafted PU were evaluated by surface, structural and thermal analysis. The results suggest that, among the methods studied in this work, the modification by gamma irradiation (GI) seems to be the most promising, since this method gives high values of grafting yield and has the advantage of providing a clean modification, meaning that no initiator is needed.     

Spatial distribution and decrease of dye solar cell performance induced by electrolyte filling

The spatial performance variation of dye solar cell with standard liquid electrolyte was examined by dividing the cell into segments. Surprisingly large and permanent performance differences were found in different parts of the cell leading to significant losses in the overall cell efficiency. The decrease of open circuit voltage along the electrolyte filling direction suggests that 4-tert-butylpyridine is adsorbed non-uniformly as the electrolyte passes through the dyed TiO₂ layer during the filling process. The result indicates that non-uniform electrolyte adsorption may limit the up-scaling of dye solar cells, which calls for the examination of electrolyte filling techniques and electrolyte compositions less prone to this effect.     

Carboxymethyl cellulose on a fiber substrate: the interactions with cationic polyelectrolytes

High and low molecular weight (M_w) carboxymethyl celluloses (CMC) were adsorbed on a well-characterized fiber substrate (long fibers of a commercial bleached birch kraft pulp with the carboxylic acid groups in Na-form) to increase the charge of the fibers in a controlled fashion. The M_w played a role in the utilization of CMCs as a strength additive in paper sheets nearly doubling the tensile strength with the high M_w CMC. Swelling properties of the CMC treated fibers were measured with water retention value (WRV). The WRV increased more with the high M_w CMC. The swelling was further tuned by two highly cationic polyelectrolytes; high M_w poly(diallyldimethyl ammonium chloride) (PDADMAC) and low M_w polybrene (hexadimethrine bromide, [3,6]-ionene). They were chosen because of their known ability to neutralize the anionic charge either exclusively on the surface or in the whole fiber, respectively. Adsorption of PDADMAC could reduce WRV of the CMC pre-treated fibers to the level of the untreated reference, while polybrene adsorbed pulps with 3–10 times more cationic polyelectrolyte deswelled the fibers only slightly more than the surface neutralized fibers. These results indicated surface conformation differences with low and high M_w CMCs. While the conformation did play a role after physical alteration (drying and rewetting) of the fibers, the paper sheets produced from these fibers showed remarkable differences. In extreme cases, the strength of the paper could be retained after drying (low M_w CMC + PDADMAC) or paper, resistant to disintegration, could be achieved (CMC + polybrene).     

Performance and early applications of a versatile double aberration-corrected JEOL-2200FS FEG TEM/STEM at Aalto University

Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80 kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80 kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube.     

Top–down mass spectrometry reveals new sequence variants of the major bovine seminal plasma protein PDC‐109

The major protein of bovine seminal plasma, PDC‐109, is a 109‐residue polypeptide that exists as a polydisperse aggregate under native conditions. The oligomeric state of this aggregate varies with ionic strength and the presence of lipids. Binding of PDC‐109 to choline phospholipids on the sperm plasma membrane results in an efflux of cholesterol and choline phospholipids, which is an important step in sperm capacitation. In this study, Fourier transform ion cyclotron resonance mass spectrometry was used to analyze PDC‐109 purified from bovine seminal plasma. In addition to the previously known PDC‐109 variants, four new sequence variants were identified by top–down mass spectrometry. For example, a protein variant containing point mutations P10L and G14R was identified along with another form having a 14‐residue truncation in the N‐terminal region. Two other minor variants could also be identified from the affinity‐purified PDC‐109. These results demonstrate that PDC‐109 is naturally produced as a mixture of several protein forms, most of which have not been detected in previous studies. Native mass spectrometry revealed that PDC‐109 is exclusively monomeric at low protein concentrations, suggesting that the protein oligomers are weakly bound and can easily be disrupted. Ligand binding to PDC‐109 was also investigated, and it was observed that two molecules of O‐phosphorylcholine bind to each PDC‐109 monomer, consistent with previous reports. Copyright © 2012 John Wiley & Sons, Ltd.     

Chemoenzymatic Hydrogen Production from Methanol through the Interplay of Metal Complexes and Biocatalysts

Microbial methylotrophic organisms can serve as great inspiration in the development of biomimetic strategies for the dehydrogenative conversion of C₁ molecules under ambient conditions. In this Concept article, a concise personal perspective on the recent advancements in the field of biomimetic catalytic models for methanol and formaldehyde conversion, in the presence and absence of enzymes and co-factors, towards the formation of hydrogen under ambient conditions is given. In particular, formaldehyde dehydrogenase mimics have been introduced in stand-alone C₁-interconversion networks. Recently, coupled systems with alcohol oxidase and dehydrogenase enzymes have been also developed for in situ formation and decomposition of formaldehyde and/or reduced/oxidized nicotinamide adenine dinucleotide (NADH/ NAD⁺). Although C₁ molecules are already used in many industries for hydrogen production, these conceptual bioinspired low-temperature energy conversion processes may lead one day to more efficient energy storage systems enabling renewable and sustainable hydrogen generation for hydrogen fuel cells under ambient conditions using C₁ molecules as fuels for mobile and miniaturized energy storage solutions in which harsh conditions like those in industrial plants are not applicable.     

Oscillations of the random argument of a wiener process in the Skorokhod representation

A sequence of independent random variables with zero mean generates, by applying to it the A. V. Skorokhod representation, a sequence of random arguments of a Wiener process. At the proof of limit theorems for sums of independent random variables with the use of this representation, there arises the question of the stability of the sequence of the random arguments. In the paper the law of the iterated logarithms yields exact bounds for the oscillation of this sequence.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Institute im. V. A. Steklova Akademii Nauk SSSR, Vol. 177, pp. 83–91, 1989.