Toward an understanding of the turbidity measurement of fleterocoagulation rate constants of dispersions containing particles of different sizes

Our previous studies have shown that the determination of coagulation rate constants by turbidity measurement becomes impossible for a certain operating wavelength (that is, its blind point) because at this wavelength the change in the turbidity of a dispersion completely loses its response to the coagulation process. Therefore, performing the turbidity measurement in the wavelength range near the blind point should be avoided. In this article, we demonstrate that the turbidity measurement of the rate constant for coagulation of a binary dispersion containing particles of two different sizes (heterocoagulation) presents special difficulties because the blind point shifts with not only particle size but also with the component fraction. Some important aspects of the turbidity measurement for the heterocoagulation rate constant are discussed and experimentally tested. It is emphasized that the T-matrix method can be used to correctly evaluate extinction cross sections of doublets formed during the heterocoagulation process, which is the key data determining the rate constant from the turbidity measurement, and choosing the appropriate operating wavelength and component fraction are important to achieving a more accurate rate constant. Finally, a simple scheme in experimentally determining the sensitivity of the turbidity changes with coagulation over a wavelength range is proposed.

Complex stress functions and plastic zone sizes for notch cracks subjected to various loading conditions

In this paper, the conformal mapping method is used to solve the plane problem of an infinite plate containing a central lip-shaped notch subjected to biaxial loading at a remote boundary or a surface uniform pressure on the notch. The stress intensity factors KI and KII are obtained by the derived complex stress functions. The simple analytical expressions can be applied to the situation of cracks originating from a circular or an elliptical notch. The plastic zone sizes for such notch cracks are subsequently evaluated in light of the Dugdale strip yield concept. The results are consistent with available numerical data.

Seed-Mediated Growth of Nearly Monodisperse Palladium Nanocubes with Controllable Sizes

Nearly monodisperse Pd nanocubes with controllable sizes were synthesized through a seed-mediated growth approach. By using Pd nanocubes of 22 nm in size as seeds, the morphology of the as-grown nanostructures was fixed as single-crystalline, which enabled us to rationally tune the size of Pd nanocubes. The formation mechanism of initial 22 nm nanocubes was also discussed. The size-dependent surface plasmon resonance properties of the as-synthesized Pd nanocubes were investigated. Compared with previous methods, the yield, monodispersity, perfection of the shape formation, and the range of size control of these nanocubes are all improved.

Nucleation and growth of glycine crystals with controllable sizes and polymorphs on Langmuir-Blodgett films

Control of crystal polymorph and size is very important in many application fields. Herein we demonstrate that Langmuir-Blodgett (LB) films of stearic acid (SA) and octadecylamine (ODA) can serve as templates and generate different polymorphs of glycine crystals. In the neutral aqueous solutions, gamma-glycine crystallizes on LB films of ODA while the polymorphic outcome becomes the (x-form on LB films of SA. These observed results could be explained by the electrostatic interactions and geometric lattice matching at the LB film/crystal interfaces, respectively. By keeping the appropriate supersaturation, we have successfully controlled the number of crystals grown on LB films; for example, in some certain cases, only one piece of crystal was grown on LB films in solution. Therefore, large crystals of centimeter size could be prepared. These experimental results suggest a new approach to produce an organic crystal with bulk scale.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Effects of rubber content and temperature on unstable fracture behavior in ABS materials with different particle sizes

The fracture behavior of ABS materials with a particle diameter of 110 nm and of 330 nm was studied using instrumented Charpy impact tests. The effects of rubber content and temperature on fracture behavior, deformation mode, stable crack extension, plastic zone size, J-integral value, and crack opening displacement were investigated. In the case of a particle size of 110 nm, the material was found to break in a brittle manner, and the dominant crack mechanism was unstable crack propagation. Fracture toughness increases with increasing rubber content. In the case of a particle size of 330 nm, brittle-to-tough transition was observed. The J-integral value first increases with rubber content, then levels off after the rubber content is greater than 16 wt %. The J-integral value of a particle diameter of 330 nm was found to be much greater than that of 110 nm. The J-integral value of both series first increased with increasing temperature until reaching the maximum value, after which it decreased with further increasing temperature. The conclusion is that a particle diameter of 330 nm is more efficient than that of 110 nm in toughening, but for both series the effectiveness of rubber modification decreases with increasing temperatures higher than 40 degreesC because of intrinsic craze formation in the SAN matrix at temperatures near the glass transition of SAN. (C) 2000 John Wiley & Sons, Inc.

Dependence of linear electro-optic coefficient on difference in the atomic sizes in zinc blende crystals

Covalent radii of the bonding elements have strong effects on the linear electro-optic coefficients of zinc blende crystals; these effects can be quantitatively determined by investigating the relation between the difference in the atomic sizes rho and the magnitude of the linear electro-optic tensor coefficient r(41). It is interesting to note that for the same cation Zn2+, Ga3+, or In3+ the magnitude of r(41) increases with increased covalent radius of the bonded anion r(beta). Especially with the increasing tendency of the parameter rho, the magnitude of r(41) of crystals that have a same cation will increase suddenly when the value of r(beta) becomes larger. (C) 1997 Academic Press.