Category: Incremental nanotechnology

If you ask a materials scientist to choose a material, the first things they will think about are things like strength, fracture toughness and stiffness – the fundamental mechanical properties that characterise the material. A materials technologist will consider these properties too, but into the equation will also go how much the material costs and how easy it is to manufacture. But when a consumer is deciding whether to buy a product made from the material, it’s not numbers like the fracture toughness that swing the decision. It’s much more intangible qualities, the way the material looks and feels, and the way the design integrates the properties of the component materials with the form of the object, that determine whether the purchase is made, the price the product can command, and in many cases the pleasure that the consumer gets from owning and using the artefact. We can create new materials with controlled nanostructures, designing combinations of properties like strength and toughness to order. But who’s thinking about how to design those human-centred properties that are so important in giving value to materials? Only engineers care about fracture toughness, and most people aren’t engineers.

These reflections arise after a day spent in the London offices of the design house, the Conran Partnership. A small group of scientists, on the one hand, and designers, on the other, met to talk about industrial design, what’s good and bad about plastics, and whether there’s any way in which one could relate the emotional response of a consumer to a material to some scientific description. Some things are obvious – the heft that comes from high density, the apparent coldness of metal that comes from its high thermal conductivity. Some are less obvious, though – why is the anodised aluminium finish of my Apple Powerbook quite so desirable? It’s clearly something to do with roughness and texture, but what, exactly? And what about the time dependence of these qualities – what is it about leather, hardwoods and natural stone that make them age so gracefully?

The promise of nanotechnology – even the incremental kind that is a natural development of the last fifty years of materials science – is that it will allow us to design materials with properties to order. Because materials development is done by scientists and engineers, the properties that we tend to concentrate on are the physical ones like strength and stiffness. Now we need to understand the other factors that make an object desirable so we can design materials that fulfill those needs.

Mark Reed, from Yale, was another speaker at a meeting I was at in New Jersey last week. He gave a great talk about the promise and achievement of molecular electronics which I thought was both eloquent and well-judged.

The context for the talk is provided by the question marks hanging over Moore’s law, the well-known observation that the number of transistors per integrated circuit, and thus available computer power, has grown exponentially since 1965. There are strong indications that we are approaching the time when this dramatic increase, which has done so much to shape the way the world’s economy has changed recently, is coming to an end.

The semiconductor industry is approaching a “red brick wall”. This phrase comes from the International Technology Roadmap for Semiconductors, an industry consensus document which sets out the technical barriers that need to overcome in order to maintain the projected growth in computer power. In the technical tables, cells which describe technical problems with no known solution are coloured red, and by 2007-8 these red cells proliferate to the point of becoming continuous – hence the red brick wall.

A more graphic illustration of the problems the industry faces was provided in a plot that Reed showed of surface power density as a function of time. This rather entertaining plot showed that current devices have long surpassed the areal power density of a hot-plate, are not far away from the values for a nuclear reactor, and somewhere around the middle of the next decade will surpass the surface of the sun. Now I find the warm glow from my Powerbook quite comforting on my lap but carrying a small star around with me is going to prove limiting.

So the idea that molecular electronics might help overcome these difficulties is quite compelling. In this approach, individual molecules are used as the components of integrated circuits, as transistors or diodes, for example. This provides the ultimate in miniaturisation.

The good news is that (despite the Sch??n debacle) there are some exciting and solid results in the field. The simplest devices, like diodes, have two terminals, and there is no doubt that single molecule two-terminal devices have been convincingly demonstrated in the lab. Three terminal devices, like transistors, seem to be vital to make useful integrated circuits, though, and there progress has been slower. It’s difficult enough to wire up two connections to a single molecule, but gluing a third one on is even harder. This feat has been achieved for carbon nanotubes.

What’s the downside? The carbon nanotube transistors have a nasty and underpublicised secret – the connections between the nanotubes and the electrodes are not, in the jargon, Ohmic – that means that electrons have to be given an extra push to get them from the electrode into the nanotube. This makes it difficult to scale them down to the small sizes that would be needed to make them competitive with silicon. And the single molecule devices have the nasty feature that every one is different. Conventional microelectronics works because every one of the tens of millions of transistors on something like a Pentium are absolutely identical. If the characteristics of each of the components were to randomly vary the whole way we currently do computing would need to be rethought.

So it’s clear to me that molecular electronics remains a fascinating and potentially valuable research field, but it’s not going to deliver results in time to prevent a slow-down in the growth of computer power that’s going to begin in earnest towards the end of this decade. That’s going to have dramatic and far-reaching effects on the world economy, and it’s coming quite soon.

Howard Lovy reports a televised encounter between some nanopants and a sticky fluid, in which the nanopants came off the worse.

Nanopants (or nanotrousers to any local readers) are garments whose fabric has been treated with the textile treatments of the Nano-tex corporation to improve their resistance to staining. Nanopants have become a bit of a touchstone to where people stand in the controversial matter of deciding what nanotechnology actually is. To followers of the Drexlerian view of nanotechnology (MNT) they are a symbol of how the word nanotechnology has been debased to cover all kinds of mundane, incremental applications of technology, far removed from the original grand vision. The pro-MNT blogger Glenn Harlan Reynolds simply calls them fake. But Nano-tex, to the nanobusiness community, is a splendid example of how nanotechnology can transform even traditional industries. Where does the truth lie?

I looked up the Nano-tex patents, in an attempt to establish whether the nano in these pants is real or simply marketing hype. There are 18 of them, and it isn’t obvious which technology is used in which product, but the general idea is clear enough. A typical product will be a copolymer – two or more chemically different polymer chains that are chemically attached to each other. One type of polymer will be hydrophilic, and this will tend to stick to a cotton or wool fibre, and the other part is hydrophobic. These hydrophobic bits of the chain will arrange themselves away from the textile surface, presenting a water and stain resistant surface to the outside world.

Two questions – is this novel, and is it nanotechnology? From the point of view of a scientist (rather than a patent lawyer) it clearly isn’t that new. It’s the same basic idea as 3M’s Scotchgard‚Ñ¢, invented in 1956 – this technology is also based on a copolymer, in this case an acrylic backbone on which water-repellant fluorocarbon side-chains are grafted. This works in just the same way as Nano-tex’s molecules – the acrylic backbone sticks to the fibre surface, leaving the water-repellant side-chains to coat the surface with a non-stick layer. But nonetheless, I do think it is nanotechnology, albeit of rather a rudimentary kind. A molecule has been defined with a specific architecture which codes the information it needs to form a specific nanoscale structure (in this case, sticky hydrophilic bits next to the textile surface, non-stick hydrophobic bits on the outside). It exploits the principle of self-assembly, which, as I explain in chapter 5 of my book Soft Machines, is the principle by which the sophisticated nano-machines of cell biology are constructed, and which we will learn to use in ever more sophisticated ways to make synthetic nano-devices.

But if nanopants really are nanotechnology, does that not imply that 3M have been doing nanotechnology since at least 1956, without using the label? Well, in this sense, yes. So the final lesson should probably be that the use of nano as a label for incremental products like this does owe a lot to marketing, but that doesn’t mean they don’t involve sophisticated technology. It’s just that other products without the nano label may in fact be just as nano-enabled.