▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

Temperature-sensitive aqueous microgels.

The ability to pattern materials in three dimensions is critical for several technological applications, including composites, microfluidics, photonics, and tissue engineering. Direct-write assembly allows one to design and rapidly fabricate materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in direct ink writing are reviewed with an emphasis on the push towards finer feature sizes. Opportunities and challenges associated with direct ink writing are also highlighted.

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Direct ink writing of 3D functional materials

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.

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Colloidal Processing of Ceramics

Design and Production of Nanoparticles Formulated From Nano-Emulsion Templates-A Review

The stability of fluorocarbon emulsions the effect of the chemical nature of the oil phase

The rheology of concentrated polyelectrolyte-coated latices

Several methods for measuring the compressive strength of strong particulate gels are available, including the centrifuge method, whereby the strength as a function of volume-fraction is obtained parametrically from the dependence of equilibrium sediment height upon acceleration. The analysis used conventionally due to Buscall & White (1987) ignores the possibility that the particulate network might adhere to the walls of the centrifuge tube, even though many types of cohesive particulate gel can be expected to. The neglect of adhesion is justifiable when the ratio of the shear to compressive strength is small, which it can be for many systems away from the gel-point, but never very near it. The errors arising from neglect of adhesion are investigated theoretically and quantified by synthesising equilibrium sediment height versus acceleration data for various degrees of adhesion and then analysing them in the conventional manner. Approximate correction factors suggested by dimensionless analysis are then tested. The errors introduced by certain other approximations made routinely in order to render the data-inversion practicable are analysed too. For example, it shown that the error introduced by treating the acceleration vector as approximately one-dimensional is minuscule for typical centrifuge dimensions, whereas making this assumption renders the data inversion tractable.

Correction of wall adhesion effects in the centrifugal compression of strong colloidal gels

The extent of reaction in reactive solid mixtures, comprising two or more particulate components, can be significantly affected by the presence of unavoidable compositional fluctuations in these systems. This is particularly the case where the size of the reaction zone is of the order of a few particle diameters. Results of detailed computer simulations, aimed at investigating the influence of composition and particle size ratios, on the fluctuations and thus the extent of reaction in reactive solid mixtures, are reported here. These data are complemented by analytical calculations performed for systems in certain limiting cases. In accord with experimental observations on certain classes of such systems, namely pyrotechnics, both the simulation and the analytical results show that the extent of reaction attains its maximum value at compositions, which compared to the stoichiometric ratio, are somewhat richer in the minor component. The deviation of the optimal composition from stoichiometry becomes more pronounced for small reaction zone sizes, where the relative compositional fluctuations are larger. The effect of altering the particle size ratio, for systems where the stoichiometric volume ratio is different to 1:1, is found to be markedly asymmetric. Reducing the size of the particles of the minor component is seen to dramatically improve the extent of reaction in the system. In contrast, any observed improvements, arising from a reduction in the size of the major component, are found to be at best marginal. The analytical calculations allow an insight into these result to be gained.

Richard Buscall

Papers

The stability of fluorocarbon emulsions the effect of the chemical nature of the oil phase

The rheology of concentrated polyelectrolyte-coated latices

Correction of wall adhesion effects in the centrifugal compression of strong colloidal gels

Extent of reaction in energetic particulate mixtures: Role of composition and particle size ratio

Polyelectrolyte-Stabilized Latices