Summary: Comb‐like macromolecules were adsorbed on mica and imaged by scanning force microscopy in real time as they underwent a transition from an extended worm‐like conformation to globuli and vice versa. The conformational transition was effected by coadsorption of ethanol and water molecules. Coadsorption of the small molecules allowed manipulation of the adherence and spreading of the macromolecules, thus effecting the reptation like stretching and collapse of the single molecules.
SFM images of three individual PMA‐g‐PnBuA brush molecules on mica 27 min (left, first collapse cycle) and 18 min (right, second collapse cycle) after injection of ethanol into the sample space. 相似文献
In 2-trifluoromethylphenyldifluorophosphine the proximate couplings 4J(19F31P) and 5J(19F19F) are + 68.3 and + 8.3 Hz, respectively. 1J(13C31P) is ?57.0 Hz, 2J(13C-1, 10F) is + 9.9 Hz and 2J(13C-6, 13C-6, 31P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the 31P and ring 13C nuclei. 相似文献
We introduce a hierarchy of sets which can be derived from the integers using countable collections. Such families can be coded into countable algebraic structures preserving their algorithmic properties. We prove that for different finite levels of the hierarchy the corresponding algebraic structures have different classes of possible degree spectra. 相似文献
Ab initio electronic structure theory calculations on cluster models support the characterization of the signature absorption spectrum of a solvated hydroxyl OH radical as a solvent-to-solute charge transfer state modulated by the hydrogen-bonding environment. Vertical excited states in OH(H2O)n clusters (n = 0-7, 16) calculated at the TDDFT level of theory (with companion calculations at the EOM-CCSD level of theory for n 相似文献
Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly. 相似文献
Pt/carbon black samples fabricated from dimethyl (1,5-cyclooctadiene) platinum(II) in supercritical CO2 are characterized in relation to possible applications in methanol fuel cell. The problem of precise material characterization is addressed in frames of X-ray diffractometry, transmission electron microscopy, and electrochemical techniques of the true surface area determination. The catalysts with Pt loading of 20–40 wt.% consist of nm-size particles, with the lattice defectiveness dependent on the fabrication mode. To check the effect of support, various types of carbon blacks (Vulcan XC72R and acetylene black AC-1) are used. In contrast to commercial HiSpec catalysts, no pronounced increase of particle size with Pt loading is found. Specific steady-state activity towards methanol oxidation appears to be essentially higher than for commercial catalysts, mostly because the self-poisoning effects are less pronounced. As for poisoning of Pt with organic species (resulting from the ligand of precursor), its effects are demonstrated to be minor after CO or methanol adsorption accompanied by desorption of contaminating by-product. 相似文献
