AVS2002 Session SE+NS-MoA: Nanoparticle and Nanofiber Surface Technologies
Monday, November 4, 2002 2:00 PM in C-111B
SE+NS-MoA-1 Investigation of Erbium Dispersion in Electrospun Nanofiber Matrices
W. Kataphinan, R.D. Ramsier, E.A. Evans, D.H. Reneker (University of Akron)
Thermally stable nanofibers can be doped with molecular and atomic species. As an example, electrospun nanofibers made from polydiphenoxyphosphazene (PDPP) have been doped with erbium (Er) using Er(III) nitrate hydrate dissolved in ethanol. The Er/PDPP matrices are thermally stable up to 150 C in air for extended periods of time. Nanofibers electrospun from ceramic precursors are stable up to much higher temperatures. Infrared spectroscopy, electron microscopy and other techniques are used to quantify the influence of the electrospinning parameters (voltage, solvent, concentration, etc.) on the structural and spectral properties of the nanofibers and the dispersion of the Er-based dopants. Differences between methods for doping the fibers will be described based on these results. These results expand the useful operating temperature range of polymer nanofiber systems as well as the use of nanofiber matrices as a support for the dispersion of molecular and atomic scale dopants.
SE+NS-MoA-2 Grafting of Poly (N-isopropylacrylamide) in Surfactant Templated Mesoporous Silica Films and Particles
Q. Fu, G.V. Rama Rao, J. Huang, G.P. Lopez (The University of New Mexico)
Surface-initiated atom transfer radical polymerization (ATRP) is an effective and versatile method used to generate grafted polymers on surfaces. We report grafting of a poly (N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer, into a mesoporous silica matrix using the ATRP technique. PNIPAAM exhibits a lower critical solution temperature (LCST) at 32°C in water, below which it is in an expanded conformation and soluble in water. Above the LCST, PNIPAAM is in compacted state and insoluble in water. Synthesis of mesoporous films and monodisperse microparticles was carried out through an acid catalyzed sol-gel process using a surfactant template approach. We used a non-ionic surfactant (Pluronic-P123) and a cationic surfactant (cetyltrimethyl ammonium bromide) for the present study. The LCST of the hybrid films was established by static contact angle measurements. These hybrid materials exhibited thermo responsive behavior by changing from hydrophilic to hydrophobic state with change in temperature. X- ray diffraction and transmission electron microscopic studies on the films and particles confirmed the presence of an ordered porous structure before and after ATRP. The grafting of the polymer onto the pore surface was confirmed by drastic decrease in pore volume of the particles after ATRP. Pore opening and closing due to contraction and expansion of PNIPAAM was studied by fluorescent dye uptake behavior of particles by monitoring the fluorescence intensity in flow cytometry experiments. It was found that the uptake of the dye into the pores was obstructed below LCST, and above LCST, the polymer was collapsed and facilitated the passage of dye into the mesopores. The dye in the pores was entrapped by cooling the particles to below LCST and subsequently the dye was released by washing with water above LCST. These materials have potential application in controlled release, chemical separation and control of fluidic transport.
SE+NS-MoA-3 Structural, Optical and Photocatalytic Properties of Nd@super 3+@ Doped TiO@sub 2@ Nanoparticles
W. Li, S.I. Shah, C.-P. Huang (University of Delaware); O. Jung (Chosun University, Korea)
TiO@sub 2@ nanoparticles, with Nd@super 3+@ dopant concentration ranging from 0 to 1.5 at.%, were synthesized using metallorganic chemical vapor deposition. The dopant concentration and TiO@sub 2@ stoichiometry were verified by x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. Particle size and crystal structure were obtained by x-ray diffraction and high-resolution transmission electron microscopy which showed the nanoparticles are polycrystalline anatase with 22 nm average particle size. Red shifts of TiO@sub 2@ absorption edge with the increase of Nd@super 3+@ concentration were observed by spectrophotometery. 1.5 at.% Nd@super 3+@ shows ~0.15 eV red shift. The photoreactivities of Nd@super 3+@ doped and undoped TiO@sub 2@ were measured by studying the degradation of 2-chlorophenol solutions under ultra violet radiation. Nd@super 3+@ position in TiO@sub 2@ lattice critically affects the photocatalytic activity of TiO@sub 2@ nanoparticles. Nd@super 3+@ position in TiO@sub 2@ lattice was studied by using XRD peak shifts. The results of these studies will be presented.
SE+NS-MoA-4 Computational Studies of Gas-Phase Growth of Soot Nanoparticles Using Fully-Integrated Integrated Molecular Dynamics and Kinetic Monte Carlo Methods
A. Kubota, W.J. Pitz, C.K. Westbrook (Lawrence Livermore National Laboratory)
Combustion under fuel-rich gas conditions leads to the formation of soot nanoparticles. We study this process of carbon nanoparticle formation through the use of fully-integrated kinetic Monte Carlo and molecular dynamics methods. Rule-based polymerizatio n and gas-surface kinetics are used in the chemical kinetic mechanism. This mechanism includes competitive H-abstraction and H-addition, as well as carbon-species addition, termination and cyclodehydrogenation and ring-closure reactions. We demonstrate that nanoparticle structure, morphology and rates are strongly coupled to the chemical kinetics as well as the gas-phase conditions. We compare modeling results with available experimental measurements.
SE+NS-MoA-5 Enhancement of High Temperature Oxidation Resistance of Fe-Cr-Ni Alloys Using Nanocrystalline CeO2 Coating Synthesized by Microemulsion Technique
S. Seal, S. Patil, S. Kuiry (University of Central Florida)
Fe-Cr-Ni alloys are usually subjected to high temperature oxidation during their various processing stages like rolling, forging and heat treatment. Extensive scaling losses are found to occur in these components in such aggressive environments at elevated temperatures. Therefore, development of coating that imparts oxidation resistance to Fe-Cr-Ni alloys is important not only for applications of these alloys at elevated temperatures but also to protect the oxidation losses during high temperature processing. The present study investigates the effectiveness of nano-sized CeO2 coating to enhance high temperature oxidation resistance of Fe-Cr-Ni alloys. Nanocrystalline CeO2 particles were synthesized with micro-emulsion technique using AOT [sodium bis(2-ethylhexyl) sulphosuccinate] as a surfactant. Kinetics of high temperature oxidation was studied on both bare and coated rectangular specimens in dry air. The scale cross section and surface morphology were characterized by using SEM, EDS, XPS and HRTEM studies.
SE+NS-MoA-7 Formation and Optical Properties of Peridically Arranged Silver Nanoparticles by Irradiation with Linear Polarized Ultrashort Laser Pulses
A. Heilmann, A. Kiesow, D. Katzer (Fraunhofer-Institute for Mechanics of Materials Halle, Germany); A. Podlipensky, G. Seifert, H. Graener (Martin-Luther-University Halle, Germany)
We report on a new and simple method to generate periodically ordered metallic, wire-like structures in an organic polymer-like matrix by irradiating thin films with series of ultrashort laser pulses. The films, which were deposited by alternating plasma polymerization and metal evaporation, are characterized by a two-dimensional particle size and shape distribution, i.e. all silver particles are arranged on one plane within the plasma polymer matrix. After laser irradiation with linearly polarized ultrashort (pulse duration < 150 fs), the nanostructure of the film changes from a relatively uniform particle distribution to a formation of an ensemble with metal particle nanowires. This was demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Material ablation during laser irradiation was not observed. The individual nanowires are between 100 to 250 nm wide with equal line space ratio. The obtainable structure size is not a function of the focusability of the laser and is significantly smaller than the laser wavelength used. The orientation of these wire-like structures is correlated to the linear polarization of the laser pulses, and is independent on the write direction of the laser beam. This dependence on laser polarization results in anisotropic optical properties. The optical extinction spectra were measured by locally resolved optical spectroscopy and by using linearly polarized light. The shift of the extinction peak depending on different steps of nanowire formation was analyzed. The optical spectra were correlated with the different nano-structures and various models were discussed to explain the material transport in the film.