A New Approach to Engineering the Materials of the Future

Transmission electron microscope (TEM) images and GISAXS
paEerns (insets) of two giant surfactant thin­‐film samples.
The TEM images show ordered nanoscale paEerns.

Some of the most interesting and fascinating electronic devices that will someday be available to consumers, from paper-thin computers to electronic fabric, will be the result of advanced materials designed by scientists. Indeed, some remarkable discoveries have already been made. To innovate further, scientists must learn how to precisely engineer the chemical structures of materials at the nanoscale in such a way as to yield specific macroscopic properties and functions.

A research group, jointly working at theNational Synchrotron Light Source, has found a new way to do just that. They have synthesized a new class of macromolecules that organize themselves, or “self-assemble,” into various ordered structures with feature sizes smaller than 10 nanometers. Called “giant surfactants,” these large molecules mimic the structural features of small surfactants (substances that significantly lower the surface tension between two liquids, such as detergents), but have been transformed into functional molecular nanoparticles by being “clicked” with polymer chains. The resulting materials are unique because they bridge the gap between small molecule surfactants and traditional block copolymers and thus possess an interesting “duality” in their self-assembly behaviors.

“This class of materials provides a versatile platform for engineering nanostructures that have features smaller than 10 nanometers, which is a scale that is very relevant to the blueprints of nanotechnology and microelectronics,” said the study’s corresponding scientist Stephen Cheng, a researcher in the University of Akron’s College of Polymer Science and Polymer Engineering. “More broadly, we are also interested in how our results could help advance our understanding of the chemical and physical principles that underlie self-assembly.”

Surfactants play a huge role in our everyday life, although most people are unaware of them. They are present in household cleaners and soaps, adhesives, paint, ink, plastics, and many, many other products. Naturally, they are a key part of materials research.

Giant surfactants have the potential to be even more versatile than their smaller counterparts because they have the advantages of both a polymer and a surfactant. They are of particular interest to the electronics industry because they can spontaneously self-assemble into nanodomains just a few nanometers in size. This length scale must be achieved in order to allow the continual downsizing of computer chips but proven very difficult to achieve for conventional technologies. The production of nanopatterned thin films – which are the foundation of modern computer chips – could be directly affected by giant surfactants. If films can be produced with smaller nanoscale features, they could lead to denser, faster computer chips.

The group used several techniques to study different giant surfactant samples in thin-film form, as well as in bulk form and in solution. These techniques included grazing-incidence small-angle x-ray scattering (GISAXS) at NSLS beamline X9. GISAXS is suited to studying thin film samples that have ordered nanoscale features, typically between 5 and 20 nanometers, and can tell researchers about the shape, size, and orientation of these features, among other information. It is widely used to study self-assembled thin films with nanoscale features.

This research is published in the June 18, 2013 issue of the Proceedings of the National Academy of Sciences. The team, which includes scientists from the University of Akron, National Tsing Hua University (Taiwan), McMaster University (Canada), and Peking University (China), has also described this research in a pending patent application.

http://www.bnl.gov/newsroom/news.php?a=24808

All aboard the nanotrain network

Tiny self-assembling transport networks, powered by nano-scale motors and controlled by DNA, have been developed by scientists at Oxford University and Warwick University.

The system can construct its own network of tracks spanning tens of micrometres in length, transport cargo across the network and even dismantle the tracks.

The work is published in Nature Nanotechnology and was supported by the Engineering and Physical Sciences Research Council and the Biotechnology and Biological Sciences Research Council.

Researchers were inspired by the melanophore, used by fish cells to control their colour. Tracks in the network all come from a central point, like the spokes of a bicycle wheel. Motor proteins transport pigment around the network, either concentrating it in the centre or spreading it throughout the network. Concentrating pigment in the centre makes the cells lighter, as the surrounding space is left empty and transparent.

The system developed by the Oxford University team is very similar, and is built from DNA and a motor protein called kinesin. Powered by ATP fuel, kinesins move along the micro-tracks carrying control modules made from short strands of DNA. 'Assembler' nanobots are made with two kinesin proteins, allowing them to move tracks around to assemble the network, whereas the 'shuttles' only need one kinesin protein to travel along the tracks.
Green dye-carrying shuttles sit idle on the tracks before refuelling

'DNA is an excellent building block for constructing synthetic molecular systems, as we can program it to do whatever we need,' said Adam Wollman, who conducted the research at Oxford University's Department of Physics. 'We design the chemical structures of the DNA strands to control how they interact with each other. The shuttles can be used to either carry cargo or deliver signals to tell other shuttles what to do.

'We first use assemblers to arrange the track into 'spokes', triggered by the introduction of ATP. We then send in shuttles with fluorescent green cargo which spread out across the track, covering it evenly. When we add more ATP, the shuttles all cluster in the centre of the track where the spokes meet. Next, we send signal shuttles along the tracks to tell the cargo-carrying shuttles to release the fluorescent cargo into the environment, where it disperses. We can also send shuttles programmed with 'dismantle' signals to the central hub, telling the tracks to break up.'

This demonstration used fluorescent green dyes as cargo, but the same methods could be applied to other compounds. As well as colour changes, spoke-like track systems could be used to speed up chemical reactions by bringing the necessary compounds together at the central hub. More broadly, using DNA to control motor proteins could enable the development of more sophisticated self-assembling systems for a wide variety of applications.

Video: The time-lapse video shows the network, with tracks shown in red, handling a cargo of fluorescent green dye over a period of eight minutes. There's a flash of bright green when the dye-carrying nanoshuttles are first added, which soon find their way onto the tracks. The shuttles are given ATP fuel at 209 seconds in, powering their journey to the centre of the network. Once they reach the centre at 319s, clean-up shuttles with the 'release' signal are sent in. These remove the dye from the network, leaving the tracks empty but for a few stragglers.

The time is shown in seconds (top left) and the scale bar is 10 micrometres (bottom left).

Source: http://www.ox.ac.uk/media/news_stories/2013/131111_1.html