1,721,177 research outputs found
Production of Ultrahigh-Molecular-Weight Polyethylene/Pristine MWCNT Composites by Half-Titanocene Catalysts
No full textMWCNT/Ultrahigh-molecular-weight polyethylene (UHMWPE) composites, where pristine MWCNTs are well dispersed in the UHMWPE matrices, are produced using MWCNT/half-titanocene hybrids as catalysts. The diameter of the UHMWPE-coated MWCNT strands produced is about 30-70 nm, while the diameter of the pristine MWCNTs used is 10-15 nm. UHMWPE composites with a molecular weight greater than 2 x 10(6) are produced
(X)OVER-BAR-CONTROL AND R-CONTROL CHARTS FOR SKEWED POPULATIONS
No full textThis paper proposes a heuristic method based on a weighted variance concept of setting up control limits of (X) over bar and R charts for skewed populations. It provides asymmetric control limits in accordance with the direction and degree of skewness estimated from the sample data, by using different variances in computing upper and lower control limits. For symmetric populations, however, these control limits are equivalent to those of Shewhart control charts. The new heuristic control charts are compared by Monte Carlo simulation with Shewhart charts and the geometric control charts of Ferrell. When the underlying population is Weibull or Burr's, the heuristic charts are found to perform better than Shewhart or geometric charts as the skewness increases
Reactivity control of carboxylic acid-terminated self-assembled monolayers on gold: Acid fluoride versus interchain carboxylic anhydride
No full textReactions that occur at interfaces often show different behaviors from their solution analogues. In this paper, we demonstrated how proximity effect, one of the unique phenomena at interfaces, could control the product distributions of interfacial reactions. Self-assembled monolayers (SAMs) of 16-mercaptohexadecanoic acid on gold surfaces were treated with cyanuric fluoride and pyridine, which are generally used for forming acid fluorides from carboxylic acids in the solution-based reaction. After the treatment, two different products, acid fluorides (AFs) and interchain carboxylic anhydrides (ICAs), were controllably obtained at surfaces under different reaction conditions with keeping the reagents the same. Various factors, such as the concentrations of reagents, reaction time, and additives, affected the product distribution (or the reaction pathway) at surfaces. We found that one of the key factors in controlling the reaction pathway was a relative contribution from the proximity effect of adjacent carboxylic acid chains in the SAMs (kinetic control) and the equilibrium shift (thermodynamic control). The relative reactivity of AF- and ICA-presenting surfaces toward primary amines, such as undecylamine and [((6-aminohexyl)amino)carbonyl]ferrocene, was also investigated, in terms of the number and the ordering of the amines coupled onto the surfaces
Surface-initiated polymerization of L-lactide: Coating of solid substrates with a biodegradable polymer
No full textFluoro-N,N,N ,N -tetramethylformamidinium hexafluorophosphate: A reagent for formation of interchain carboxylic anhydrides on self-assembled monolayers
No full textIn this paper, we report the reactivity of fluoro-N, N, N', N'-tetramethylformamidinium hexafluorophosphate ( TFFH), a reagent for transformation of carboxylic acids into acid fluorides in solution, toward self-assembled monolayers ( SAMs) of 16-mercaptohexadecanoic acid on gold. Contrary to the solution-based reactions, we found that only interchain carboxylic anhydrides ( ICAs), not acid fluorides ( AFs), were obtained at surfaces by the facile interchain reaction under most reaction conditions studied. AFs were found to be formed only when tetrabutylammonium fluoride, a reagent inducing fast decomposition of ICAs, was added to the reaction mixture. The reactivity of TFFH toward carboxylic acid-terminated SAMs was different from that of cyanuric fluoride, which has been reported previously ( Langmuir 2005, 21, 11765-11772). This study provides more insight into the role of the proximity effect in SAM-based reactions as well as another approach to the formation of ICAs from carboxylic acid-terminated SAMs
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