ChemMatCARS Nuggets - Nanoscience

Assembling Nanoparticles at Liquid Interfaces

While solid surface are obvious sites for self-assembly, we have shown that particle self-assembly can also take place at the interface between two immiscible liquids. One advantage of doing nano-assembly here is that the fine balance between thermal fluctuations and interfacial energy tend to ‘select’ particles of exactly the right size. The opens up a possible avenue for making precision nano-materials for such applications as opto-electronics. A number of microscopy techniques have been used to study the self-assembly of particles which can hybridized with organic molecules and then cross-linked to produce membranes with regular nanometer-sized pores.

Synchrotron-based techniques such as small angle x-ray scattering at ChemMatCARS at the Advanced Photon Source allow us to look at particle ordering during the formation process on length scales far smaller than can be seen with any optical microscope.

While our original studies where made using cadmium selenide nanoparticles, we have found more recently that harmless plant viruses like cow-pea mosaic virus can be used to build these nano-structures at liquid interfaces in much the same way. An advantage in using biologically derived building blocks is the fact that they can be produced in large quantities with exactly the same size and shape.

Below, a synchrotron small-angle scattering image showing Bragg rods (straight vertical lines of intensity) which give us the inter-particle spacing (6.8nm) of the CdSe nanoparticles as they self assemble at a liquid interface.

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