Search results for "Chain length"
showing 10 items of 54 documents
Environmental and biological factors are joint drivers of mercury biomagnification in subarctic lake food webs along a climate and productivity gradi…
2021
Subarctic lakes are getting warmer and more productive due to the joint effects of climate change and intensive land-use practices (e.g. forest clear-cutting and peatland ditching), processes that potentially increase leaching of peat- and soil-stored mercury into lake ecosystems. We sampled biotic communities from primary producers (algae) to top consumers (piscivorous fish), in 19 subarctic lakes situated on a latitudinal (69.0-66.5 degrees N), climatic (+3.2 degrees C temperature and +30% precipitation from north to south) and catchment land-use (pristine to intensive forestry areas) gradient. We first tested how the joint effects of climate and productivity influence mercury biomagnific…
Monolayers of asymmetrical diethylalkanoat disulfides on gold(111):.the influence of chain length difference on atomic force microscope images
1998
Several symmetrical and asymmetrical long-chain diethylalkanoat disulfides were synthesized and character- ized. The differences in the chain lengths of the disul- fides ranged between zero and five methylene units. Self- assembled monolayers of these disulfides formed on Au(111) surfaces were studied by atomic force microscopy (AFM) in order to obtain information about the origin of the image contrast. Domains with hexagonal lattices (lattice constants 5:2- 5:3 A) were detected for all derivatives, independent of the chain length differences. This indicates that the contrast arises roughly at a depth of 4- 8 A in the monolayers at imag- ing forces between 0: 2a nd 3n N. For SAMs of diethyl…
The Structure, Stoichiometry and Properties of C-S-H Prepared by C3S Hydration Under Controlled Condition
1998
Hydrations of tricalcium silicate undertaken by keeping constant lime concentration in solution in an open system and in diluted suspensions for different values of [CaO] ranging between 6.5 and 30 mmol/1 show that the lime concentration in solution is the parameter which determines the main characteristics of the reaction and products. The stoichiometry of C3S hydration products vanes with lime concentration in the same way as synthetic C-S-H until C/S c.a. 1.5 corresponding to about [CaO] =20 mmol/1. Beyond this concentration, single phase C-S-H samples were obtained with 1.8<C/S<2. The discontinuity of the variation of stoichiometry with concentration is characteristic of an invariant po…
Synthesis of Water-Soluble Copolymers Carrying Long-Chain (C12 to C30 ) Aliphatic Moieties
2011
Water-soluble copolymers from mono-1-alkyl itaconates and N-vinyl-2-pyrrolidone are synthesized and characterized. Themono-1-alkyl itaconates are prepared from itaconic anhydride and the related alcohol: 1-dodecanol, 1-octadecanol, 1-docosanol, and 1-triacontanol. The mono-1-triacontyl itaconate is synthesized fromplant growth regulator policosanols extracted from Agave fourcrouydes, where 1-triacontanol is the major product. The reactivity ratios, calculated according to the Mao-Huglin method for copolymerizations conducted to medium-high conversions, indicate a tendency toward alternation for all copolymerization reactions. Water solubility of copolymers is provided as a function of copol…
Gas—liquid chromatographic analyses
1984
Abstract The gas chromatography (GC) of n -alkyl acetates (CH 3 COOR), chloroacetates (CH 2 ClCOOR), dichloroacetates (CHCl 2 COOR) and trichloroacetates (CCl 3 COOR), where the alcohol chain length (R) varied between 1 and 8, and certain of their monochlorinated derivatives, 176 compounds altogether, has been studied on SE-30 and OV-351 glass capillary columns under the same operating conditions. The isomeric monochlorinated esters are eluted in direct order from the 1- chloro to the ω-chloro isomer, the separation of the isomers being complete on OV- 351. On SE-30, however, the peaks of the 6- and 7-chlorooctyl esters are partly overlapped. The separation of the mixtures of odd- and e…
Röntgenographische untersuchungen an linearen oligourethanen
1961
Zwei polymerhomologe Reihen von Diol-oligo-urethanen wurden rontgenographisch untersucht. Die vor allem im Kleinwinkelbereich durchgefuhrten Messungen fuhrten zu dem Ergebnis, das die gefundenen Langperioden bis zum Diol-okta-urethan eine Funktion des Molekulargewichtes sind und dann uber einen weiten Molekulgrosenbereich bis zum Polymeren einschlieslich konstant bleiben. Two homologous polymeric series of diol-oligo-urethanes were studied by X-rays, particularly in the small-angle range. Up to a certain chain length (diol-octa-urethanes) the observed long periods are a function of the molecular weight. Then they remain constant over a wide range up to the polymer inclusively.
1979
The demixing behavior of 20 representatives of the system oligo(dimethylsiloxane)/oligo(propylene glycol) (ODMS/OPG)1 is investigated at pressures up to 1 500 bar. The degrees of oligomerization range from 2 to 5 for the first and from 1 to 57, 6 for the second component. The experimental results are compared with those for the previously studied system oligoisobutene/oligo(propylene glycol) (OIB/OPG). In both cases the observed upper critical temperatures Tc increase with the number of monomeric units of the less polar component, whereas they run through a minimum when the number of monomeric units of the glycol is raised. For the present system the Tc values are found to be considerably h…
Die Kristallisation von Mehrkomponentensystemen aus hochpolymeren Stoffen
1977
Es wird untersucht, welche Anderungen im Kristallisationsverhalten hochpolymerer Stoffe auftreten, wenn man von einem Einkomponentensystem auf ein Mehrkomponentensystem ubergeht. Beispiele fur Mehrkomponentensysteme sind Homopolymere mit einer breiten Molekulargewichtsverteilung, Mischungen aus verschiedenen Homopolymeren, gequollene Polymere, Blockcopolymere und statistische Copolymere. Das Auftreten einer Molekulargewichtsverteilung ausert sich vor allem bei einer Kristallisation mit gestreckten Ketten, und zwar in der Weise, das eine Fraktionierung nach Molekullangen auftritt. Des weiteren bewirkt sie eine Verbreiterung des Schmelzbereichs. Die Anwesenheit eines zweiten nichtkristallisie…
Understanding Digestive Ripening of Ligand-Stabilized, Charged Metal Nanoparticles
2017
Most syntheses of thiolate-protected metal nanoparticles (NPs) include a thermochemical step in which the as-prepared, polydisperse NPs are transformed to a narrower size distribution in a poorly understood process known as digestive ripening (DR). Previous theoretical approaches considered either surface and electrostatic contributions or surface and ligand-binding contributions. We show that the three contributions are needed to obtain theoretical predictions in agreement with experimental observations. Although statistical thermodynamics does not clarify mechanistic details, it certainly provides valuable insights on the DR process. Remarkably, a relatively simple theory with no fitting …
Monodisperse Dialkoxy-Substituted Oligo(phenyleneethenylene)s
2006
Individual but connected synthetic routes for the preparation of the all-E-configured 2,5-dipropoxy-substituted oligo(1,4-phenyleneethenylene)s 1a–g were developed. An increasing number of conjugated stilbene units from n = 1 to n = 11 led to a convergent bathochromic shift (Δλ = λ∞ − λ1 = 127 nm) in the UV/Vis absorption. An exponential function for the convergence of the absorption energies (wavelengths) in conjugated systems is proposed. By a simple extrapolation of this function the effective chain length may be determined.