Francisco Arias

Making Negative Poisson's Ratio Microstructures by Soft Lithography**

1186 O WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 0935-9648/99/1410-1186

Fabrication of metallic heat exchangers using sacrificial polymer mandrils

17.50+.50/0 Adv. Mater. 1999, 11, No. 14 quenching to room temperature. As a result, the polarization bandwidth was found to increase by a factor of 2.4 over what was expected of a constant-pitch film. The increased bandwidth was attributed to a pitch gradient resulting from photoinduced racemization of the chiral dopant at the irradiated surface with simultaneous diffusion through the film. This is the first demonstration of a pitch gradient generated in the mesomorphic fluid state and then frozen in a glassy chiral-nematic film.

Making Honeycomb Microcomposites by Soft Lithography

This paper demonstrates the use of poly(dimethylsiloxane) (PDMS), polyurethane (PU), epoxy, and poly(methyl methacrylate) (PMMA) as mandrils to fabricate metallic heat exchangers having 300-700 /spl mu/m internal channels. The mandrils were prepared using two soft lithographic techniques-replica molding and microembossing. To fabricate the heat exchangers, the polymeric mandrils were coated with a thin layer of metal by thermal evaporation or sputtering; this layer acted as the cathode for electrodeposition of a shell of nickel or copper that was 100 /spl mu/m thick. The polymers were removed by burning them out at 400/spl deg/C in air, or by dissolving them with a tetrahydrofuran solution of tetrabutylammonium fluoride. Studies of heat dissipation showed that the nickel heat exchangers with features that range in size from 150-750 /spl mu/m have thermal resistances ranging from 0.07 to 0.12/spl deg//sup -2/C W/sup -1/ cm at flow rates of water of /spl sim/20 L h/sup -1/ and pressures of 8.6-83/spl times/10/sup 3/ N m/sup -2/.

Electrochemical studies of S-nitrosothiols.

492 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 0935-9648/99/0604-0492

Trace Analysis of Bromate in Potato Snacks Using High-Performance Liquid Chromatography−Tandem Mass Spectrometry

17.50+.50/0 Adv. Mater. 1999, 11, No. 6 [4] P. T. Tanev, M. Chibwe, T. J. Pinnavaia, Nature 1994, 368, 321. [5] P. Behrens, Angew. Chem., Int. Ed. Engl. 1996, 35, 515; Angew. Chem. 1996, 108, 561 [6] a) D. M. Antonelli, J. Y. Ying, Curr. Opin. Colloid Interface Sci. 1996, 1, 523. b) D. M. Antonelli, J. Y. Ying, Angew. Chem., Int. Ed. Engl. 1995, 34, 2014; Angew. Chem. 1995, 107, 2202. [7] U. Ciesla, S. Schacht, G. D. Stucky, K. Unger, F. J. Schüth, Angew. Chem., Int. Ed. Engl. 1996, 35, 541; Angew. Chem. 1996, 108, 597. [8] P. Liu, J. Liu, A. Sayari, Chem. Commun. 1997, 577. [9] a) D. M. Antonelli, J. Y. Ying, Angew. Chem., Int. Ed. Engl. 1996, 35, 426; Angew. Chem. 1996, 108, 461. c) D. M. Antonelli, A. Nakahira, J. Y. Ying, Inorg. Chem. 1996, 35, 3126. [10] D. M. Antonelli, J. Y. Ying, Chem. Mater. 1996, 8, 874. [11] J. S. Reddy, A. Sayari, Catal. Lett. 1996, 38, 219. [12] M. S. Wong, D. M. Antonelli, J. Y. Ying, Nanostruct. Mater. 1997, 9, 165. [13] Z. R. Tian, J. Y. Wang, N. G. Duan, V. V. Krishnan, S. L. Suib, Science 1997, 276, 926. [14] T. Sun, J. Y. Ying, Nature, 1997, 389, 704. [15] G. A. Somorjai, An Introduction to Surface Chemistry and Catalysis, Wiley, New York 1994. [16] C.-G. Wu, T. Bein, Chem. Mater. 1994, 6, 1109.

Fabrication and characterization of microscale sandwich beams

S-nitrosothiols (RSNO), such as SNAP, GSNO, and Glc-SNAP-1 exhibited a single, totally irreversible, diffusion controlled reduction peak at potentials of -0.97 V, -0.98 V and -0.91 V, respectively, vs. Ag/AgCl (3 M NaCl) reference electrode. This corresponded to the nitric oxide (NO) release from the S-nitrosothiols. A possible mechanism is proposed for the reduction process.

Study of Langmuir monolayers of crown-ether C60 derivatives and their interaction with different subphase ions

A simple, sensitive, and selective high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method in the negative-ion electrospray ionization (ESI(-)) mode was validated for the quantitation of bromate (BrO(3)(-)) in potato snacks. Ground snack specimens ( approximately 0.5 g/sample) are spiked with Br(18)O(3)(-), stable-isotope labeled bromate internal standard (IS), and vortexed with a mixture of distilled/deionized water (dd water) and heptane. Subsequently, the specimens are centrifuged, and a small portion of the aqueous extract is isolated, diluted with dd water (1:4), and analyzed by HPLC-MS/MS. The methodology has a quantitation range of 10-1000 ppb, an accuracy of 1.5-7.5%, and a precision of 5.2-13.4% across the concentration range.

ELECTROCHEMICAL PROPERTIES OF FULLERENES AND FULERENE DERIVATIVES: A POSSIBLE ROUTE TO ENDOHEDRAL COMPLEXES

Microscale sandwich beams with cell diameters and wall widths down to 150 and 15 mm, respectively, and having both metallic and polymer/metal cores were produced through fabrication methods that combined photolithography and electrodeposition. Various core structures were used, including some with negative Poisson’s ratio. The bending response was investigated and compared with beam-theory predictions. Most of the cores evaluated had sufficient shear stiffness that the bending compliance was relatively high and dominated by the face sheets. Two of the core configurations were “soft” and exhibited behavior governed by core shear. The relative dimensions of the cores evaluated in this study were far from those that minimize the weight, because of fabrication constraints. The development of an ability to make high-aspect ratio cores is an essential next step toward producing structurally efficient, lightweight microscale beams and panels.

Portable interstitial fluid monitoring system

The Langmuir monolayers of two crown-ether C 60 derivatives with different crown size (18-crown-6. and 15-crown-5) were studied by surface spectrophotometry and Brewster angle microscopy. The surface pressure-area (π-A) isotherms of the C 60 derivatives on pure water and different subphase ions were obtained. The limiting area of the isotherms depends on both the crown size and the presence of subphase ions. The larger crown size gave the larger limiting area of the isotherm. The addition of K + , Ba 2+ or NH 4 + to the subphase stabilized the monolayers and increased the limiting areas of the monolayer. Brewster angle microscopy shows different aggregation properties of crown-ether C 60 derivative monolayers on pure water compared with those on K + , Ba 2+ or NH 4 + subphases.

Method of manufacturing microneedle structures using soft lithography and photolithography

An overview of the redox chemistry of the fullerenes, starting with that of C60 and going on to that of some of its derivatives, is presented. The main focus revolves around the cathodic electrochemistry of C60 in homogeneous solution as well as of some of its derivatives at very negative potentials. Potentials as negative as -3.3 V vs the ferrocene/ferricinium (Fc/Fc+) couple are reported. While underivatized C60 and C70 can be reversibly reduced to their corresponding hexaanions, their derivatives exhibit chemical reactions following their fourth electrochemical reduction. The results for some derivatives are interpreted in terms of chemical reactions that lead to the formation of stable diphenyl carbanions. During these reactions, it is proposed that a “hole” is opened on the C60 sphere, and thus the process is envisioned as a potential preparative method for endohedral cation complexes.