The group of scientists, from the University of California, Berkeley, the Berkeley National Laboratory, Kyoto Institute of Technology and Tohoku University, used small molecules that are attracted to the nanoparticles and certain parts of polymers. This combination orders the nanoparticles into complex shapes within the polymer material. Small molecules that change either their affinity for the polymers or their own shape in response to heat or light were then used, allowing the nanoparticle ordering within the polymers to be altered on demand. Published online in [Xu et al., Nature Materials, doi: 10.1038/nmat2565], the study shows how this approach can be used with a variety of different blends to order the nanoparticles at different length scales with high precision. It also simplifies the material fabrication because the nanoparticles can be used without further chemistry.
The main significance of the work can be seen in the use of small molecules to mediate particle-polymer interactions to selectively incorporate nanoparticles within block copolymer microdomains, the use of molecular ordering of small molecules to direct spatial arrangement of nanoparticles within copolymer microdomains, and the external stimuli-responsiveness – that is, using non-covalent interactions to direct the assembly.
The team worked on the basis that non-covalent interactions are both important and powerful, and that sophisticated structures can be obtained by blending various components and directing inter-molecular interactions. As the team's approach is essentially plug-and-play and each component can be readily switched, it may enable relatively rapid advances in these studies. The research also aids an understanding of multi-length assemblies in multi-component systems, how to measure various contributions from different components, and how to manipulate nanoscopic building blocks in a confined geometry.
The team are now examining the structure/property relationship of these nanocomposites in bulk, and are looking at how to manipulate the nanoparticle assemblies in thin films with control over their macroscopic alignment and inter-particle ordering, which should enable them to fabricate devices in a thin film setting. In addition, further research into the properties of nanoparticle assemblies may lead to some functional devices on a larger scale, especially as process used here is compatible with existing fabrication process in the microelectronic industry.