New Developments in Colloid Science

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Original entry: Xu Zhang, APPHY 225, Fall 2009

Reference

New Developments in Colloid Science D.A. Weitz and W.B. Russel, MRS Bull. Feb 2004 83 (2004)

Keywords

colloids, colloidal materials, "directed" assembly, rheology, suspensions

Summary

This article summarizes several new developments of colloid science in two aspects: "directed" assembly of colloidal particles and understanding in rheology of colloidal suspensions.

Directed Assembly

Various methods

1) Using depletion interaction

Controllable elements: 1.surface treatment 2.solvent choice 3.addition of other materials

2) Applying additional stresses ( Van Blaaderen ) Ex. a hard wall that restricts the states of the colloidal suspension, electric and magnetic fields, surface stresses induced by drying, oder imposed by patterned surfaces, gravitational effects,etc.

3)Using interactions between colloidal particle Because thermal energy allows particles to explore phase space and achieve the lowest-energy structure, the thermalization of the particles in response to Brownian motion is essential to allowing them to self-assemble. <math>k_B T</math>

Main Obstacle

The surface energy drives the interface of the particle to be spherical, which places fundamental limitations on the structures that can be built.An important limitation comes in making photonic-bandgap structures

Solutions

1)Mix particles of different sizes and create binary alloy crystal structures

2)Encapsulate spherical particles in emulsion droplets that are then collapsed by drying (https://sites.google.com/a/manoharan.deas.harvard.edu/www/publications V.N. Manoharan, M.T. Elsesser, and D.J. Pine, “Dense Packing and Symmetry in Small Clusters of Microspheres”, Science 301: 483–487 (2003))