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Aric Opdahl Roger A. Phillips Gabor A. Somorjai 《Journal of Polymer Science.Polymer Physics》2004,42(3):421-432
The surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004 相似文献
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P. Miranda Jr. J. Zukerman-Schpector J. R. Matos M. F. Máduar E. M. Aricó M. Linardi L. B. Zinner G. Vicentini 《Journal of Thermal Analysis and Calorimetry》2004,75(2):577-582
The complexes [Ln(pic)3(DTSO)3] (Ln=La, Lu and Y; pic=picrate; DTSO=1,3-dithiane-1-oxide) were synthesized and characterized. Indirect structural determination by far infrared
spectroscopy is presented. Results from thermal decomposition of these complexes by TG/DTG and DSC techniques are reported.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Leung KC Aricó F Cantrill SJ Stoddart JF 《Journal of the American Chemical Society》2005,127(16):5808-5810
The versatility and efficiency of dynamic covalent chemistry (DCC) has been exploited in the convergent synthesis of mechanically interlocked dendrimers that are based upon the mutual recognition expressed between secondary dialkylammonium ions and crown ether-like macrocycles. Reversible imine bond formation is employed to clip two acyclic fragments, one of them a diformylpyridine unit bearing a dendritic side chain, and the other a complementary dianiline in the shape of the di(o-aminophenyl)ether of tetraethylene glycol, around each arm of a tritopic trisammonium ion core, thereby affording a branched [4]rotaxane. This template-directed strategy has been demonstrated to work in very high yields (>90%) with successive generations (G0-G2) of a modified Fréchet-type dendritic wedge attached to the 4-position of the diformylpyridine unit. Reduction of these dynamic dendritic systems is achieved upon treatment with borane.THF and results in kinetically stable compounds. The inherent modularity of the overall process should allow for the rapid and straightforward access to many other analogous mechanically interlocked systems in which either the branched core or the dendritic periphery can be modified to suit the needs of any given application of these molecules. Indeed, the dynamic nature of the initial thermodynamically mediated assembly could be utilized in order to amplify particular products from a potential library as a result of a selective recognition process. 相似文献
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Two front instabilities in a reaction-diffusion system are shown to lead to the formation of complex patterns. The first is an instability to transverse modulations that drives the formation of labyrinthine patterns. The second is a nonequilibrium Ising-Bloch (NIB) bifurcation that renders a stationary planar front unstable and gives rise to a pair of counterpropagating fronts. Near the NIB bifurcation the relation of the front velocity to curvature is highly nonlinear and transitions between counterpropagating fronts become feasible. Nonuniformly curved fronts may undergo local front transitions that nucleate spiral-vortex pairs. These nucleation events provide the ingredient needed to initiate spot splitting and spiral turbulence. Similar spatiotemporal processes have been observed recently in the ferrocyanide-iodate-sulfite reaction. 相似文献
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[reaction: see text] A highly regio- and stereoselective bis-stannylation of unsymmetrically substituted butadiyne 3 provides bis-stannane 4. Selective lithiation of the internal tin residue effects a 1,4-retro-Brook rearrangement to afford vinylsilane 5. This was elaborated into the novel diethynylethene 1, which also functions as a masked triyne. 相似文献
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We describe a fast solver for linear systems with reconstructible Cauchy-like structure, which requires O(rn
2) floating point operations and O(rn) memory locations, where n is the size of the matrix and r its displacement rank. The solver is based on the application of the generalized Schur algorithm to a suitable augmented matrix, under some assumptions
on the knots of the Cauchy-like matrix. It includes various pivoting strategies, already discussed in the literature, and
a new algorithm, which only requires reconstructibility. We have developed a software package, written in Matlab and C-MEX,
which provides a robust implementation of the above method. Our package also includes solvers for Toeplitz(+Hankel)-like and
Vandermonde-like linear systems, as these structures can be reduced to Cauchy-like by fast and stable transforms. Numerical
experiments demonstrate the effectiveness of the software. 相似文献
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J. Ledesma-Garcia I. L. Escalante-Garcia Thomas W. Chapman L. G. Arriaga V. Baglio V. Antonucci A. S. Aricò R. Ornelas Luis A. Godinez 《Journal of Solid State Electrochemistry》2010,14(5):835-840
Dendrimer-encapsulated Pt nanoparticles (G4OHPt) were prepared by chemical reduction at room temperature. The G4OHPt, with
average diameters of ca. 2.7 nm, were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric
analysis. Electrocatalytic behavior for oxygen reduction reaction was investigated using a rotating disk electrode configuration
in an acidic medium, with and without the presence of methanol (0.01, 0.1, and 1 M). Kinetic studies showed that electrodes
based on Pt nanoparticles encapsulated inside the dendrimer display a higher selectivity for ORR in the presence of methanol
than electrodes based on commercial Pt black catalysts. Also, the dendritic polymer confers a protective effect on the Pt
in the presence of methanol, which allows its use as a cathode in a direct methanol fuel cell operating at different temperatures.
Good performance was obtained at 90 °C and 2 bar of pressure with a low platinum loading on the electrode surface. 相似文献
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A. M. Castro Luna A. Bonesi W. E. Triaca A. Di Blasi A. Stassi V. Baglio V. Antonucci A. S. Aricò 《Journal of nanoparticle research》2010,12(1):357-365
Three cathode catalysts (60% Pt/C, 30% Pt/C and 60% Pt–Fe/C), with a particle size of about 2–3 nm, were prepared to investigate
the effect of ethanol cross-over on cathode surfaces. All samples were studied in terms of structure and morphology by using
X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic behavior in terms of oxygen
reduction reaction (ORR) was investigated and compared using a rotating disk electrode (RDE). The tolerance of cathode catalysts
in the presence of ethanol was evaluated. The Pt–Fe/C catalyst showed both higher ORR activity and tolerance to ethanol cross-over
than Pt/C catalysts. Moreover, the more promising catalysts were tested in 5 cm2 DEFC single cells at 60 and 80 °C. An improvement in single cell performance was observed in the presence of the Pt–Fe catalyst,
due to an enhancement in the oxygen reduction kinetics. The maximum power density was 53 mW cm−2 at 2 bar rel. cathode pressure and 80 °C. 相似文献
10.
Mixing the dipyrido[24]crown-8 derivatives carrying one or two formyl group(s) on the 4 position(s) of their pyridine ring(s) with a 3-fold symmetrical trisammonium ion template in a 3:1 ratio in CD3NO2 results in the formation of thermodynamically stable [4]pseudorotaxanes which, upon addition of a 1,3,5-trisaminobenzene cap, form mechanically interlocked molecular bundles with one and two caps, respectively, by virtue of dynamic imine bond formation. 相似文献