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Abstract: Flash NanoPrecipitation (FNP) is a novel approach for producing functional nanoparticles stabilized by amphiphilic block copolymers. FNP involves the rapid mixing of a hydrophobic active (organic) and an amphiphilic di-block copolymer with a non-solvent (water) and subsequent co-precipitation of nanoparticles composed of both the organic and copolymer. During this process, the particle size distribution (PSD) is frozen and stabilized by the hydrophilic portion of the amphiphilic di-block copolymer residing on the particle surface. That is, the particle growth is kinetically arrested and thus a narrow PSD can be attained. To model the co-precipitation process, a bivariate population balance equation (PBE) has been formulated to account for the competitive aggregation of the organic and copolymer versus pure organic–organic or copolymer–copolymer aggregation. Aggregation rate kernels have been derived to account for the major aggregation events: free coupling, unimer insertion, and aggregate fusion. The resulting PBE is solved both by direct integration and by using the conditional quadrature method of moments (CQMOM). By solving the competitive aggregation model under well-mixed conditions, it is demonstrated that the PSD is controlled primarily by the copolymer–copolymer aggregation process and that the energy barrier to aggregate fusion plays a key role in determining the PSD. It is also shown that the characteristic aggregation times are smaller than the turbulent mixing time so that the FNP process is always mixing limited. [ABSTRACT FROM AUTHOR]

Abstract: Physical structure of pixelated detectors provides a unique tool to evaluate the effects of different types of defects in the semiconductor material that is used to fabricate the detectors. The spectroscopic performance measured for individual pixels or groups of pixels can be used to correlate point defects or fields of inhomogeneities within the material with the charge collected from photoelectric events. A block of single crystal mercuric iodide of approximately 18×18mm2 area and between 6 and 10mm thick is prepared. The homogeneity of this material is then investigated with light in the transparent region for HgI2 using an optical microscope. Several types of defects can be identified in this way by the scattering of light, for example, single large inclusions or voids and areas of haziness consisting of fields of small inclusions. Standard procedures are used to fabricate from this block a pixelated detector with a 121-pixel anode structure. The performance of each pixel is measured, and differences in charge collection are correlated with the optical data. Measurement data are presented, and possible mechanisms of the interactions between the defects and the charge carriers are discussed. [Copyright &y& Elsevier]

Abstract: An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of latex spheres suspended in an aqueous solution undergoing laminar Taylor–Couette flow was carried out according to the following program. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method) and with predictions using spatial average shear rates. The mean particle size evolution predicted by CFD and QMOM using appropriate kinetic expressions that incorporate information concerning the particle morphology (fractal dimension) and the local fluid viscous effects on aggregation collision efficiency match well with the experimental data. [Copyright &y& Elsevier]