Publications by Year: 2001

Lee, T. ; Yao, N. ; Imai, H. ; Aksay, I. A. Barium titanate nanoparticles in block copolymer. Langmuir 2001, 17, 7656-7663.Abstract
CubicBaTiO3 particles of10nmwere crystallized predominantly within the hydroxylated polybutadiene matrix of a phase separated triblock copolymeric thin film of polystyrene-polybutadiene-polystyrene (Kraton D1102). The barium titanated Kraton thin film had remnants of the cylindrical morphology of a plain Kraton thin film with an interdomain spacing of 23 nm. The procedure of barium titanation consisted of three steps: (1) in situ hydroxylation of the polybutadiene matrix of an annealed Kraton thin film, (2) regioselective deposition of barium titanium methoxypropanoxide (BaTi(OCH2CH(CH2)OCH3)6) on the hydroxylated polybutadiene matrix, and (3) hydrothermal reduction of the organometallic complexes in anNH3/H2Oatmosphere at 80 °C for 24 h. Isolated water clusters in step 3, condensed from theNH3/H2O atmosphere of 1 M NH4OH(aq) at 80 °C in the alkoxide-Kraton films, were believed to have a typical diameter of no more than 23 nm at a pH of 14. They gave a high pH environment to weaken the chelating effectamongalkoxides and the organic matrix and provided a spatial confinement for the localized nucleation and growth of cubic BaTiO3 nanoparticles.
Xu, G. F. ; Aksay, I. A. ; Groves, J. T. Continuous crystalline carbonate apatite thin films. A biomimetic approach. Journal of the American Chemical Society 2001, 123, 2196-2203.Abstract
In contrast to extensive studies on hydroxyapatite thin films, very little has been reported on the thin films of carbonated apatite (dahllite). In this report, we describe the synthesis and characterization of a highly crystalline dahllite thin film assembled via a biomimetic pathway. A free-standing continuous precursor film of carbonated calcium phosphate in an amorphous phase was first prepared by a solution-inhibited templating method (template-inhibition) at an air-water interface. A stearic acid surface monolayer acted as the template, while a carbonate-phosphate solution composed a binary inhibition system. The precursor film formed at the air/water interface was heated at 900 °C and transformed into a dense crystalline film that retained the overall shape of the precursor. The crystalline phase was characterized by XRD and IR to be a single-phase carbonate apatite, with carbonate substitutions in both type A (OH-) and type B (PO4 3-) lattice positions.
Lee, J. H. ; Prud'homme, R. K. ; Aksay, I. A. Cure depth in photopolymerization: Experiments and theory. Journal of Materials Research 2001, 16, 3536-3544.Abstract
The depth of photocuring for a model resin system was investigated as a function of photoinitiator concentration. Direct measurements of gel thickness were made from thin films of cross-linked multifunctional methacrylate monomer. The monomer, 2,2-bis{4-[2-hydroxy-3-(methacryloxy)propoxy]phenyl}propane, was polymerized in a solution of trichloroethylene with an ultraviolet laser light source at 325 nm. The monomer solutions were photocured using varying levels of both photonic energy and photoinitiator concentration. An optimal photoinitiator concentration that maximized the gel cure depth was observed. Additionally, two regimes were shown to exist in which the shrinkage (upon solvent removal) was minimized or maximized. A model was developed to probe the physics of the system. Good agreement with experiment was obtained, and the model may be employed to predict both the existence and location of the optimal photoinitiator concentration and the corresponding cure depth. The study showed that photoinitiator plays a significant role in controlling the quality and performance of the formed gel network, with special regard to thickness of cured layers. This has potential application to fields as diverse as industrially cured coatings and dental fillings, and more generally, 3-dimensional rapid prototyping techniques.
Wang, R. Z. ; Suo, Z. ; Evans, A. G. ; Yao, N. ; Aksay, I. A. Deformation mechanisms in nacre. Journal of Materials Research 2001, 16, 2485-2493.Abstract
Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamellar ceramic. The inelastic deformation of this material has been experimentally examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in compression with the boundaries oriented at 45° to the loading axis. The steady-state shear resistance tss has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress, sss » 110 MPa. The strain was associated with the formation of multiple dilatation bands at the intertablet boundaries accompanied by interlamellae sliding. Nano-asperities on the aragonite tablets and their interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. Detailed mechanisms and their significance for the design of robust ceramics are discussed.
Malik, A. - S. ; Dabbs, D. M. ; Aksay, I. A. ; Katz, H. E. Disordered Mesoporous Silicates formed by Templation of a Liquid Crystal (L3). Mater. Res. Soc. Symp. Proc. 2001, 658, 7.5.1-5.Abstract
For a wide range of technological applications the need for optically transparent, monolithic, mesoporous silicates is readily apparent. Potential areas of utility include filtration,catalysis, and optoelectronics among many others. This laboratory has previously reported on the synthesis of such materials that are formed through the addition of tetramethoxysilane to a liquid crystal solution of hexanol, cetylpyridinium chloride, and 0.2 M hydrochloric acid, and our investigation into the properties of these materials is a continuing process. We have achieved defect and fracture free material of suitable size (0.5 cm x 3 cm diameter disks) via supercritical drying of the silicate under ethanol or CO2. The dried materials are remarkably similar to ordinary glass in strength, texture, and clarity. They possess pore volumes of ca. 1.0 cm3/g, with BET surface areas >1000 m2/g. We can re-infiltrate the dried monolith with hydroxyethylacrylate, a photo-polymerizable monomer, to create an inorganic/organic nanocomposite. There is fracturing upon re-infiltration, but preliminary tests show that the polymerization proceeds despite the mechanical failure. These findings suggest many possible applications for these unique nanocomposites.
Hayward, R. C. ; Poon, H. F. ; Xiao, Y. ; Saville, D. ; Aksay, I. Electrohydrodynamically patterned colloidal crystals, 2001.Abstract
A method for assembling patterned cryst. arrays of colloidal particles using UV illumination of an optically-sensitive semiconducting anode while using the anode to apply an electronic field to the colloidal particles. The UV illumination increases c.d., and consequently, the flow of the colloidal particles. As a result, colloidal particles can be caused to migrate from nonilluminated areas of the anode to illuminated areas of the anode. Selective illumination of the anode can also be used to permanently affix colloidal crystals to illuminated areas of the anode while not affixing them to nonilluminated areas of the anode. [on SciFinder(R)]
Li, X. P. ; Vartuli, J. S. ; Milius, D. L. ; Aksay, I. A. ; Shih, W. Y. ; Shih, W. H. Electromechanical properties of a ceramic d(31)-gradient flextensional actuator. Journal of the American Ceramic Society 2001, 84, 996-1003.Abstract
We examined the static axial displacement of a ceramic d31-gradient flextensional transducer both experimentally and theoretically. Two lead zirconate titanate systems, (PZT)/PZT and PZT/ZnO, were studied. The PZT/PZT transducers consisted of two PZT layers of different d31 coefficients. The PZT/ZnO transducers consisted of a PZT and a ZnO layer. The PZT/PZT transducers were of an inner-type dome structure. The PZT/ZnO transducers were either flat, or had an inner- or outer-type dome structure by varying the thickness ratio between the two layers or the Sb2O3 content in the ZnO layer. An inner (outer)-type transducer has the large-d31 layer on the inside (outside) of the dome structure. For the PZT/PZT transducers, the axial displacement varied with the thickness ratio and reached a maximum when the two layers had similar thickness, in agreement with the calculations. With a conductive nonpiezoelectric layer, the PZT/ZnO transducers had higher axial displacements, which varied with the thickness ratio and the Sb2O3 content, than the PZT/PZT transducers. With 6 wt% Sb2O3, the transducers were flat and the measured displacements at various thickness ratios were similar to the calculated values. With 4 wt% Sb2O3, the transducers were of an outer type. The measured axial displacements were about twice the calculated values, suggesting an enhanced d31 value because of the tensile bending stress in the PZT layer. The scaled axial displacements of the PZT/ZnO transducers with 4 wt% Sb2O3 were comparable to that of the Rainbow transducers. With 8 wt% Sb2O3, the displacements of transducers with thin PZT layers (<0.3 mm) were lower than the calculated values because of increased conductivity in the PZT layer.
Lee, T. ; Aksay, I. A. Hierarchical structure-ferroelectricity relationships of barium titanate particles. Crystal Growth & Design 2001, 1 401-419.Abstract
The aim of this paper is to dissect the hierarchical structures of BaTiO3 particles into primary, secondary, tertiary, and quaternary structural levels and to thoroughly review the corresponding structureferroelectricity relationships at all levels. This analytical framework is of growing importance for the fundamental understanding of the ferroelectric properties of BaTiO3 in microelectronic devices, especially as their structural levels are all approaching the same scale in the process of miniaturization. The identification of the most influential structure among others and the deduction of a meaningful structure-ferroelectricity relationship depend on a thorough understanding of the relationships.
Evans, A. G. ; Suo, Z. ; Wang, R. Z. ; Aksay, I. A. ; He, M. Y. ; Hutchinson, J. W. Model for the robust mechanical behavior of nacre. Journal of Materials Research 2001, 16, 2475-2484.Abstract
The inelastic deformation of nacre that leads to its structural robustness has been characterized in a recent experimental study. This article develops a model for the inelastic behavior, measured in tension, along the axis of the aragonite plates. The model is based on observations for abalone nacre that the inelasticity is associated with periodic dilatation bands. These bands contain coordinated separations at the periphery of the plates. The separations open as the material strains. The response is attributed to nanoscale asperities on the surfaces of the plates. The model calculates the stresses needed to displace the plates, resisted by elastic contacts at the asperities. The results are compared with the measured stress/strain curves.
Vartuli, J. S. ; Milius, D. L. ; Li, X. ; Shih, W. H. ; Shih, W. Y. ; Prud'homme, R. K. ; Aksay, I. A. Multilayer ceramic piezoelectric laminates with zinc oxide conductors, 2001.Abstract
A modification of the traditional unimorph flextensional actuator is provided by replacing the metal shim with an elec. conducting oxide. Comprised of Pb zirconate titanate (PZT) and ZnO that is co-sintered, the laminate composite obtains large axial displacements while maintaining moderate axial loads. The varistor properties of ZnO dictate that the conductance increases several orders of magnitude when a crit. elec. field is applied. The versatility of the processing over other actuator system facilitates miniaturization, while maintaining comparable performance characteristics. Functional gradients in the material properties are created in the green body by layering thin tape cast sheets. The unique PZT-ZnO composite not only controls the piezoelec. gradient, but permits control of the sintering kinetics leading to the processing of either flat or highly domed structures. [on SciFinder(R)]
Aksay, I. A. ; Ker, H. L. Plastically deformable aqueous ceramic slurries and methods for their manufacture, 2001.Abstract
The ceramic particles from plastically deformable aq. ceramic slurrys have on their surface a closely-packed anionic surfactant bilayer or an anionic/nonionic surfactant bilayer. Optionally, ceramic particles have on their surface a closely-packed cationic surfactant bilayer or a cationic/nonionic surfactant bilayer. Slurries prepg. includes (a) dispersing ceramic particles in an amt. of water to form an aq. ceramic slurry, (b) adding an anionic surfactant or a mixt. of an anionic and nonionic surfactant, and (c) adjusting the pH value to adsorb on the ceramic particle surface a closely-packed anionic surfactant bilayer or anionic/nonionic surfactant bilayer. [on SciFinder(R)]
Wang, R. Z. ; Suo, Z. ; Evans, A. G. ; Yao, N. ; Aksay, I. A. Scanning Electron Microscopic Analysis on the Deformation Mechanisms in Nacre. Proc. Microscopy and Microanalysis, 2001, 1118-19.
Shih, W. Y. ; Li, X. P. ; Gu, H. M. ; Shih, W. H. ; Aksay, I. A. Simultaneous liquid viscosity and density determination with piezoelectric unimorph cantilevers. Journal of Applied Physics 2001, 89, 1497-1505.Abstract
We have examined both experimentally and theoretically a piezoelectric unimorph cantilever as a liquid viscosity-and-density sensor. The fabricated piezoelectric unimorph consisted of a PbO•ZrO2•TiO2 ~PZT! layer on a thin stainless-steel plate. In addition to a driving electrode, a sensing electrode was placed on top of the PZT layer, permitting the direct measurement of the resonance frequency. The cantilever was tested using water–glycerol solutions of different compositions. In all three of the tested modes, the resonance frequency decreased while the width of the resonance peak increased with increasing glycerol content. To account for the liquid effect, we consider the cantilever as a sphere of radius R oscillating in a liquid. By including the high and low frequency terms in the induced mass and the damping coefficient of the liquid, we show that for a given liquid density and viscosity the oscillating-sphere model predicts a resonance frequency and peak width that closely agree with experiment. Furthermore, the viscosity and the density of a liquid have been determined simultaneously using the experimentally measured resonance frequency and peak width as inputs to the oscillating-sphere model. The calculated liquid viscosity and density closely agreed with the known values, indicating that our cantilever-based sensor is effective in determining viscosity and density, simultaneously. We also show that scaling analysis predicts an increase in the width of the resonance peak with decreasing cantilever size, an observation in agreement with the large peak widths observed for microcantilevers.
Yao, N. ; Ku, A. Y. ; Saville, D. A. ; Aksay, I. A. ; Musselman, I. H. TEM Studies of Disorder-Order Transition in the Acid-Catalyzed Growth of Mesoscopic Silica Thin Films. Proc. Microscopy and Microanalysis, 2001, 1226-27.