Ann Arbor (MI) - Transparent aluminum has been the dream of many ever since it was first mentioned in a popular Sci-Fi movie a couple decades back. But researchers at the University of Michigan may have done that one better. It could almost be called "transparent steel".
Scientists began with a desire to take the extremely strong nanostructures, like nanotubes, nanorods and nanosheets found at micro levels, and then build something big and usable with it. But each time they tried the strength was not carried forward into the bigger structures. There was always something making the end product quite flimsy in comparison to the strength shown at the nanoscale.
However, scientists have now overcome that difficulty with a product based on what they're calling "the velcro effect." This new polymer and glue sets up a series of hydrogen bonds between layers which, if broken, can be easily connected to other nearby locations automatically. This makes it like velcro in that if it's separated, it can be rejoined and it will be as strong as it originally was. As the materials flex and bend this bond reformation happens continuously.
To achieve this milestone, researchers began by looking at one of the strongest naturally created minerals in existence, that being mother of pearl. By examining the molecular structures and layers which comprise the seashell, scientists discovered what's significant in their unique multi-layer, brick-and-mortar construction. They then took that knowledge and put together a new plastic material that's stronger and lighter than steel, and also transparent.
Using a form of polyvinyl alcohol for glue, a large diameter wheel affixed on a custom-built machine begins the assembly process. The wheel contains a host of nanosheets, each with a different clay composite material that used in the construction. The initial substrate is a small piece of glass, about the size of a stick of chewing gum, though extremely thin. It begins the process by holding the initial glue dip. The wheel is then programmed to turn and repeatedly dip the device in the glue and then add a special layer of a clay composite material at a specific orientation.
After each glue/clay layer the material is allowed to cure before continuing with the next. It's repeated 300 times until finally the end result is a material about as thick as sheet of plastic wrap that is stronger than steel (of the same thickness), is notably lighter and transparent. The team has also worked with depositing different materials on each layer, not always based on clay. These have included carbon nanotubes, metals and various particle alloys, including some which were organic.
The assembly process works so well and generically like this because in each layer the process begins with a negatively charged material which, when dipped in the glue and "washed" with water, becomes positively charged. This allows it to attract very strongly the next layer for bonding, which changes it back to negative. The process is then repeated again and again resulting in layers which form extremely strong bonds, even at macro scales.
The researchers are presenting a paper today entitled "Ultrastrong and Stiff Layered Polymer Nanocomposites," to be published in the October 5th edition of Science magazine. Several university departments collaborated in creating this new material, including experts in aerospace, chemistry, materials science, biomedial and engineering disciplines. The University of Michigan has one of the largest research budgets of any public university, topping $130 million. Research at the university is focused on three primary areas, cellular and molecular biology, nanotechnology and information technology. Other significant scientific contributions from the university have been reported on recently, specifically in the areas of quantum computer research.
