Self-assembled tunable structures of polymer fibers ranging from wavy colloidal “fur” to highly interconnected networks were created dynamically by Center for Nanoscale Materials (CNM) users from Argonne’s Materials Science Division and their collaborators by using alternating electric fields on “sticky” epoxy colloids. The high-surface-area microstructures are tuned by the frequency and amplitude of the electric field and the surface properties of the particles. Depending on the fabrication conditions, the materials can be tailored into designed arrays of tiny mushroom-pillars, wavy “fur,” or dense gel-like networks. These high-surface-area, inexpensive, and versatile materials may have intriguing applications for emerging alternative energy technologies such as electrodes for photovoltaic cells and batteries.
Synthesis facilities in the Nanobio Interfaces Group were used during the creation of these materials. Characterization at CNM included the capabilities of FESEM, FTIR, rheometry, and electrophoretic mobility. Optical microscopy and atomic layer deposition were carried out in Argonne’s Materials Science Division.
The key ingredient is epoxy, which is added to a mixture of hardener and solvent inside an electric cell. An alternating current is run through the cell, and long, twisting fibers spring up. By tweaking the process, many different shapes can be grown: short forests of dense straight hairs, long branching strands, or “mushrooms” with tiny pearls at the tips. Interestingly, though the structures can be permanent, the process is also instantly reversible.
In one experiment, the researchers used atomic layer deposition, which deposits a molecule-thick layer of material, over the entire hairy structure to add a layer of semiconductor material. This provided proof of concept that the polymer could be incorporated into semiconductor-based renewable energy technologies. It also proved that it could survive high temperatures, up to 150°C, an essential property for many manufacturing processes.
A. Demortiere et al., “Self-assembled tunable networks of sticky colloidal particles,” Nat. Commun., 5, 3117 (2014);
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