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Self assembly process paves way for flexible electronics

A new way to assemble molecules could result in the creation of novel materials, with potential applications including flexible TVs, says a research team.

Their work focuses on the interactions between molecules and, in particular, on 'amphiphilic' molecules, which contain two distinct parts. Household detergent is an example of something that relies on interacting amphiphilic molecules. Detergent molecules comprise one part that prefers to form bonds with water (hydrophilic) and another that prefers oily substances (hydrophobic). These detergent molecules orient and assemble around oily dirt, forming small clusters that allow grease and dirt to be removed more easily.

The newly reported method is said to take the concept of amphiphilic assembly one step further by applying it to a set of hydrophobic molecules which have no hydrophilic element.
Whilst these new 'hydrophobic amphiphiles' have different 'parts', the assembly process itself is said to rely on more subtle interactions.

The research was carried out by an international team led by Dr Martin Hollamby from Keele University and Dr Takashi Nakanishi from the Japanese National Institute for Materials Science. Together, they used neutron scattering techniques at the Institut Laue-Langevin (ILL) to investigate the arrangement of these clusters and showed that hydrophobic amphiphiles can assemble into extended structures in much the same way as conventional amphiphiles.

One example is a molecule shaped like a football, but with a long tail. The amphiphile has been created from 'buckyballs' ā€“ football shaped molecules made up of 60 carbon atoms (C60) which have been modified chemically by attaching a longer 'tail' made up of chains of carbon atoms. The new compounds are said to resemble 'molecular tadpoles'. When dissolved in solvents that interact with the tails, these molecules assemble to form a core of C60 spheres and a shell of carbon chains.

The team believes that a variety of different structures can be produced by making small changes to the chemical structure of the amphiphile and to the additives (solvent or CĀ¬60) used.
This level of control over self assembly in complex molecules such as C60 is described as 'unprecedented'. "Changing the chemistry of the chains can even lead to gels made of bundled C60 wires that have a measureable photoconductivity," Dr Hollamby explained. "By adding pristine C60 in place of the solvent, we can instead prepare a sheetlike material with totally different properties".

Small angle neutron scattering data obtained on beamline D11 at the ILL was used to prove the internal structure of these clusters.

"The elements that makes up these 'molecular tadpoles' are easily located by neutrons," said the ILL's Dr Isabelle Grillo. "The small angle neutron scattering which we use at the ILL allows the self assembled systems to be characterised from the nanometre scale to tenth of microns and is adapted to see the C60 buckyballs coming together into these beautiful core structures."

One area that could be impacted by this new development is the field of molecular electronics. Carbon based electronics, say the researchers, could provide a cheaper alternative to traditional silicon technology and allow for the development of flexible handheld devices for many applications, including smartphones and tablets for watching TV. The researchers add that, by optimising how the molecules interact with each other, such new molecular electronic components could also offer improved properties, including higher efficiency and lower power consumption.

Graham Pitcher

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