Vinod P. Veedu

Nanostructured gas diffusion and catalyst layers for proton exchange membrane fuel cells

Nanostructured components are introduced in membrane electrodes assembly MEA in proton exchange membrane fuel cell as asolution to improve the performance. Single-walled carbon nanotubes and multiwalled carbon nanotubes supported platinum areused to fabricate the gas diffusion layer GDL and the catalyst layers in the MEAs, respectively. The physicochemical andelectrochemical characterizations of these nanotube-based components demonstrate excellent GDL surface morphology and uni-form distribution of the platinum catalyst over the carbon nanotube support. The fuel cell testing using these nanostructuredcomponents exhibits promising fuel cell performance using hydrogen-air and hydrogen-oxygen at ambient pressure.© 2006 The Electrochemical Society. DOI: 10.1149/1.2422751 All rights reserved.Manuscript submitted September 19, 2006; revised manuscript received October 16, 2006.Available electronically December 26, 2006.

Generally Cylindrical Orthotropic Constitutive Properties Modeling of Matrix-filled Single-walled Nanotubes: Axial Mechanical Properties

The technology of filling hollow carbon nanotubes with desirable materials has created tremendous interest in recent years. The objective of this study is to introduce analytical solutions for effective longitudinal Youngs modulus and major Poissons ratio of matrix-filled single-walled nanotubes (SWNTs). In this work, both SWNT and its filler material are considered generally cylindrical orthotropic. Analytical solutions are obtained and accordingly reduced to transversely isotropic as well as isotropic cases for both tube and filler materials, and then the results are compared with the existing solutions. For further validation, a 3-D model of a matrix-filled single-walled carbon nanotube (SWCNT) is generated and solved for displacement and strain results numerically, using the finite element method. The finite element numerical analysis is employed to verify the accuracy of the results obtained from the analytical approach for generally cylindrical orthotropic materials. Excellent agreement is achieved between the results obtained from the analytical and numerical methods. Furthermore, a parametric study is also conducted to investigate the effective properties variations of the matrix-filled nanotubes based on the variations of nanotube/filler geometry and material properties.

Experimental investigation of optimal nanoparticle inclusion for enhanced flexural performance in continuous fiber ceramic nanocomposites

This work reports the effects of using varying weight percentage of nanoparticle inclusions on mechanical performance of continuous fiber ceramic composites. The ceramic fiber reinforcement was NicalonTM, and KiON CERASET ® preceramic polymer was mixed with nanoparticle inclusions in the presence of a surfactant agent, which gave good dispersion of the particles within the matrix. Yttrium oxide nanoparticles with an average size of 29 nm was used as the inclusion with varying weight percentages of 5, 10, 15, and 20%. For comparison, samples without nanoparticles were also manufactured. Two different types of nanoparticle filled composites were manufactured. The first one followed neat preceramic polymer reinfiltration cycle, whereas the second system was manufactured with corresponding nanoparticle dispersed preceramic polymer reinfiltration. A characterization analysis of the samples using scanning electron microscopy revealed proper dispersion of nanoparticle along with good quality of the parts. In general, the weight gain percentage at each stage of reinfiltration/pyrolysis for both types of nanoparticle filled ceramic composites is consistently less than that for ceramic composites manufactured without nanoparticle. This indicates the compactness of the material and retention of shape during the B-staging. Four-point bending test was also conducted to evaluate the mechanical performance of the ceramic composite samples at room temperature. Nanoparticle filled samples consistently showed significant improvement in flexural strength compared to their counterparts without nanoparticle reinforcement.

Nanocomposites and Hierarchical Nanocomposites Development at Hawaii Nanotechnology Laboratory

This paper presents activities related to the development of nanocomposites and hierarchical nanocomposites; at the Hawaii Nanotechnology Laboratory of the Department of Mechanical Engineering of the University of Hawaii at Manoa. On nanocomposites, developments on toughening of polymeric materials employing nanoparticles and carbon nanotubes are reported. On hierarchical nanocomposites, first, mechanical properties improvements for continuous fiber ceramic composites using nanoparticles are discussed. Second, a multifunctional micro-brush using carbon nanotubes is discussed. Third, the structure of a micro-foam using carbon nanotubes is explained. Finally, the multifunctional properties improvement of a novel three-dimensional hierarchical nanocomposite employing carbon nanotubes is discussed. In closing, the effect of chirality of single-walled nanotubes on their thermomechanical properties evaluated analytically using asymptotic homogenization method and numerically employing finite element method will be explained, and analytical closed form solutions for matrix filled nanotube nanocomposites, also verified numerically, assuming generally cylindrical orthotropic properties will be reported.© 2006 ASME

Analytical and Numerical Predictions of Thermoelastic Properties of Carbon Single-Walled Nanotubes

The objective of this paper is to develop constitutive models to predict thermoelastic properties of carbon single-walled nanotubes using analytical, asymptotic homogenization, and numerical, finite element analysis, methods. In our approach, the graphene sheet is considered as a non-homogeneous network shell layer which has zero material properties in the regions of perforation and whose effective properties are estimated from the solution of the appropriate local problems set on the unit cell of the layer. Our goal is to derive working formulas for the entire complex of the thermoelastic properties of the periodic network. The effective thermoelastic properties of carbon nanotubes were predicted using asymptotic homogenization method. Moreover, in order to verify the results of analytical predictions, a detailed finite element analysis is followed to investigate the thermoelastic response of the unit cells and the entire graphene sheet network.Copyright