Study of shells yields design hints
By Julian Lee Research by an ANU chemist is providing a new insight into how living organisms produce shells - and the results may lead to more natural methods of producing advanced industrial materials. Investigating reactions called biomineralisation, Dr Stephen Holt of the Research School of Chemistry, is discovering how organisms including corals create strong and complicated structures, without the need for high-temperature industrial processes. "Biomineralisation is seen as a means by which new materials may be synthesised, and well-known materials may be produced at room temperature," he said. "This would be far easier and much cheaper." Already, mineral crystals such as aragonite and vaterite - which chemists have traditionally produced at high temperatures and pressures - can be produced at room temperature. Dr Holt's research has examined how organic chemicals, called "surfactants", can be used as templates to direct the growth of crystals such as silica and limestone in liquid baths. Unlike researchers who mix the surfactant into the bath, Dr Holt spreads it over the surface. This allows him to direct the growth of crystals from the surface, rather than growing them in random clumps throughout the bath. Dr Holt gains further control over how the crystals grow by manipulating the surfactant. One method involves pushing a barrier across the surface of the bath which forces the surfactant into certain arrangements. Another uses different types of surfactant, each creating a unique pattern. By altering the type and concentration of surfactant at the surface, Dr Holt aims to understand how the air-water interface (where the crystals are grown) and the surfactant interact to create different crystal shapes. From this he hopes to mimic some of the intricate shapes seen in nature. He is able to produce honeycomb-like sheets which, because of their high surface area, have potential use as industrial catalysts. "We could use these biomethods, which by their nature are more environmentally friendly, to replace industrial methods in factories," Dr Holt said. One particularly promising area of research is the use of self-assembling surfactants which organise themselves when placed in liquid. Dr Holt believes these are the most likely candidates for creating structures resembling those seen in nature. He said that, as human understanding of the world grows we have moved away from merely using natural products, to producing them crudely in factories and now to reproducing the methods nature uses. "Nature has an astonishing level of complexity and we have a lot to learn in how these materials are created," he said.