To make clay strong, just add glue.
Nanotechnology promises to deliver materials that will possess, on a large scale, the exceptional mechanical properties of tiny particles such as carbon nanotubes or the mineral grains that constitute clay. But because a chain is only as strong as its weakest link, it's crucial that in materials made of strong building blocks, those blocks stick together robustly.
Nicholas Kotov and his collaborators at the University of Michigan in Ann Arbor have created high-strength films by linking clay particles and polymers. The researchers dissolved clay in water, freeing its component particles—nanometer-thick flakes composed of aluminum, oxygen, and silicon atoms. They let the sheets deposit onto a glass surface, alternating them with layers of the polymer polyvinyl alcohol, "a chemical cousin of the glue that you used at school," as Kotov describes it.
Kotov says that hydrogen bonds, a relatively weak chemical linkage, formed between hydrogen atoms in the polymers and oxygen atoms in the clay. Those links glued the clay layers together, while keeping the structure flexible. Strong covalent bonds formed between the polymers' oxygen atoms and aluminum atoms along the edges of the clay sheets, joining them laterally. The team's results appear in the Oct. 5 Science.
Kotov says that clay-based composites could find applications as membranes for separating out mixtures of gases, or could lead to lighter, stronger bulletproof vests.
Department of Chemical Engineering
University of Michigan, Ann Arbor
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3074 H.H. Dow Building
Ann Arbor, MI 48109-2136