Growing Nano “Hair” for Electrodes - From the Bottom Up

Electric fields control growth of “sticky” polymer particles.

Control of the synthesis results in a diversity of self-assembled structures formed by sticky colloidal particles: array of “mushrooms” (left), wavy colloidal “fur”, dense fiber network, and three-dimensional reconstruction of the network (right). — Image courtesy of Argonne National Laboratory

The Science

Inspired by nature, a new self-assembly process for fabricating a variety of stable polymeric three-dimensional (3D) structures in response to an applied stimulus has been discovered. This work addresses a critical need for fabricating stable nano- and mesoscale fibrous (or hairy) materials that are far from equilibrium and can be assembled dynamically and reversibly in response to an applied electric field.

The Impact

This work will enable rapid and inexpensive fabrication of complex 3D structures over multiple length scales through self-assembly. As a result of this new, dynamic self-assembly approach, tunable 3D polymer array or network architectures can be formed directly on electrode surfaces. The ability to further functionalize them with conductive oxide or metal layers makes these materials promising candidates for low-cost, large surface area electrodes in batteries and organic photovoltaic cells.

Summary

Inspired by nature, a new self-assembly process for fabricating stable polymeric 3D structures in response to an applied stimulus has been discovered. Biology uses dynamic, out-of-equilibrium processes to assemble cellular components in response to specific signals. Mimicking this assembly approach to organize simple building blocks into complex architectures presents a unique opportunity in contemporary materials science, and it represents an attractive alternative to top-down nano- and mesoscale fabrication methods such as lithography. However, in practice, using this “bottom up” approach to form complex structures over multiple length scales has proven to be a difficult, since the assembled structures fall apart once the applied stimulus has been removed. Scientists at Argonne National Laboratory have addressed this problem and developed self-assembled tunable networks of microscopic polymer fibers similar to the “hairy” surfaces that exist in our bodies to protect blood capillaries from wear and infection. Using tiny, sticky epoxy droplets as the building blocks, three dimensional structures ranging from wavy colloidal “fur” to highly interconnected networks were formed on an electrode surface via dynamic self-assembly in an alternating (ac) electric field. The features of the resulting architectures were tuned by controlling the electric field and particle surface properties. Depending on the fabrication conditions, the materials can be tailored into tunable arrays of tiny mushroom-pillars or permanent wavy “hair” and dense gel-like networks, which were then further coated with an atomically thin layer of a transparent tin oxide conductor. The ability to functionalize large surface area polymer structures in this manner suggests they may find use as electrodes in photovoltaic cells and batteries.

Contact

Igor Aronson and Alex Snezhko
Argonne National Laboratory
[email protected]
[email protected]

Funding

DOE, Office of Science, Basic Energy Sciences program and the Russian Foundation for Basic Research. The research utilized the Center for Nanoscale Materials, a DOE Office of Science user facility.

Publications

Arnaud Demortière, Alexey Snezhko, Maksim V. Sapozhnikov, Nicholas Becker, Thomas Proslier and Igor S. Aranson, “Self-Assembled Tunable Networks of Sticky Colloidal Particles”, Nature Communications, volume 5, article number 3117, 2014, Published online 21 Jan 2014; [DOI: 10.1038/ncomms4117].