There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

12.2.2. Four-Wave Mixing (FWM) 4849 12.2.3. Dye Aggregation 4850 12.2.4. Optoelectronic Nanodevices 4850 12.3. Sensor 4851 12.3.1. Chemical Sensor 4851 12.3.2. Biological Sensor 4851 12.4. Catalysis 4852 13. Conclusion and Perspectives 4852 14. Abbreviations 4853 15. Acknowledgements 4854 16. References 4854 * Corresponding author E-mail: tpal@chem.iitkgp.ernet.in. † Raidighi College. § Indian Institute of Technology. 4797 Chem. Rev. 2007, 107, 4797−4862

Interparticle Coupling Effect on the Surface Plasmon Resonance of Gold Nanoparticles: From Theory to Applications

The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.

/pdf/towards-a-definition-of-inorganic-nanoparticles-from-an-4qpaj5a6q5.pdf

Towards a definition of inorganic nanoparticles from an environmental, health and safety perspective

Colloidal processing of ceramics is reviewed with an emphasis on interparticle forces, suspension rheology, consolidation techniques, and drying behavior. Particular attention is given to the scientific concepts that underpin the fabrication of particulate-derived ceramic components. The complex interplay between suspension stability and its structural evolution during colloidal processing is highlighted.

/pdf/colloidal-processing-of-ceramics-1f3f618kn7.pdf

Colloidal Processing of Ceramics

Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

The scaling behavior of the elastic properties of colloidal gels that are well above the gelation threshold is studied both theoretically and experimentally. A scaling theory was developed by considering the structure of the gel network as a collection of flocs, which are fractal objects closely packed throughout the sample. Two regimes are found based on the relative value of the elastic constant of the interfloc links to that of the flocs. In the strong-link (interfloc) regime, the elastic constant of the gels increases but the limit of linearity decreases with increasing particle concentration, whereas in the weak-link regime both the elastic constant and the limit of linearity increase with increasing particle concentration. Rheological studies on the elastic behavior of two types of boehmite alumina gels, Catapal and Dispal powders, were performed. Both types of gels in the concentration range studied showed the strong-link behavior and the results are in good agreement with the theoretical predictions. The value of the fractal dimension of the flocs D\ensuremath{\simeq}1.95, deduced from the rheological measurements, is in agreement with the value D\ensuremath{\simeq}2.04 deduced from the static light-scattering measurements on dilute suspensions. Therefore the scaling theory we developed also enables us to extract structural information from the rheological measurements.

Scaling behavior of the elastic properties of colloidal gels.

We have investigated both experimentally and theoretically the resonance frequency change of a piezoelectric unimorph cantilever due to the mass loaded at the tip of the cantilever. The piezoelectric cantilever was composed of a lead zirconate titanate (PZT) layer and a stainless steel layer. The dependence of the resonance frequency shift, Δf, with respect to a loaded mass, Δm, on the cantilever length, L, width, w, and the resonance modes was examined. For Δm much smaller than the effective mass of the cantilever, we showed that Δf/Δm increased with an increasing eigen value, νn2, and decreasing length, L, and decreasing width, w, as Δfn/Δm=−(νn2/4π)(1/L3w)(1/0.23612ρ)Ẽ/ρ, where Ẽ and ρ are the effective Young’s modulus and effective density of the unimorph cantilever that depends on the thickness fraction, Young’s modulus and density of each of the individual layers. Thus, given the same Ẽ and ρ by maintaining the same layer thickness fractions of the individual layers, Δf/Δm is increased by a fact...

Effect of length, width, and mode on the mass detection sensitivity of piezoelectric unimorph cantilevers

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.

/pdf/simultaneous-liquid-viscosity-and-density-determination-with-3qh0ir4kxh.pdf

Simultaneous liquid viscosity and density determination with piezoelectric unimorph cantilevers

A theory has been developed to examine the depolarization effect on the ferroelectric transition of small ${\mathrm{BaTiO}}_{3}$ particles. To reduce the depolarization energy, a crystal would break up into domains of different polarization. In this study, we consider cubic particles with alternating domains separated by 180\ifmmode^\circ\else\textdegree\fi{} domain walls. The depolarization energy and the domain-wall energy were incorporated into the Landau-Ginzburg free-energy density. Assuming a hyperbolic tangent polarization profile across the domain wall, the domain-wall energy \ensuremath{\gamma} and the domain-wall half thickness \ensuremath{\xi} can be obtained by minimizing \ensuremath{\gamma} with respect to \ensuremath{\xi}. To account for ${\mathrm{BaTiO}}_{3}$ not being a perfect insulator, a Schottky space charge layer beneath the particle surface that shields the interior of the crystal from the depolarization field was considered. The equilibrium polarization P and domain width D can be obtained by minimizing the total free-energy density with respect to both P and D. The results of the calculations show that the ferroelectric transition temperature of small particles can be substantially lower than that of the bulk transition temperature as a result of the depolarization effect. Consequently, at a temperature below the bulk transition temperature, the dielectric constant \ensuremath{\epsilon} can peak at a certain cube size L. These results agree with the existing experimental observations. Finally, the theory can also be applied to other ferroelectric materials such as ${\mathrm{KH}}_{2}$${\mathrm{PO}}_{4}$ or ${\mathrm{PbTiO}}_{3}$.

Size dependence of the ferroelectric transition of small BaTiO3 particles: Effect of depolarization.

We have investigated theorectically the elastic and yield behaviors of strongly flocculated colloids by first examining the yield forces between two particles within the framework of Derjaguin‐Landau‐Verwey‐Overbeck (DLVO) interactions. Under highly attractive conditions, i.e., in the absence of the secondary minimum in the DLVO potential, the radial (tensile) motion between particles is nonelastic because of the lack of an inflection point in the DLVO potential. However, the lateral (shear) motion is shown to be elastic up to a distance ymax, providing a mechanism for the observed elasticity in colloidal gels. If r0 and s0 are, respectively, the closest center-to-center and surface-to-surface distances between two particles, ymax ~ (1 2 0.5az 2 )(s0 r0) 1/2 where z is the zeta potential of the particles and a a defined constant. Moreover, the yield force between two particles is much smaller in the lateral direction than in the radial direction. These results suggest that yielding of a particulate network is likely to occur through the lateral movements between particles. The yield strain can be approximated as that at which all the bonds in a certain direction have a perpendicular displacement >ymax, resulting in e yield 5 y max r0 ~ (1 2 0.5az 2 )S s 0

/pdf/elastic-and-yield-behavior-of-strongly-flocculated-colloids-504r5pv5tx.pdf

Wan Y. Shih

Papers

Scaling behavior of the elastic properties of colloidal gels.

Effect of length, width, and mode on the mass detection sensitivity of piezoelectric unimorph cantilevers

Simultaneous liquid viscosity and density determination with piezoelectric unimorph cantilevers

Size dependence of the ferroelectric transition of small BaTiO3 particles: Effect of depolarization.

Elastic and Yield Behavior of Strongly Flocculated Colloids