The building blocks of new materials
Design of 2d soft materials Design of 2-dimensional soft materials
A deeper understanding of complex particles and the way they interact with each other could open up the possibility of researchers using them as building blocks in the design and development of new materials. We spoke to Dr Laura Rossi about her work on the synthesis of complex colloidal particles.
The aim of the project is to develop smart colloidal building blocks that interact through very specific magnetic interactions. These particles are programmed to form 2D assemblies with predefined architectures which are useful to study single-particle dynamics in 2D structures and to design novel soft materials such as membranes and coatings.
A lot of
attention in research is focused on investigating the properties of certain particles and the way they interact with each other, which could open up new possibilities in material design. Based at TU Delft in the Netherlands, Dr Laura Rossi and her colleagues’ research centres around the design and preparation of colloidal particles, which can be broadly described as any objects in a length scale of between a few nanometres and a few microns. “We’re using colloidal particles as building blocks in materials development,” she outlines. This is a challenging area, so rather than looking at complex materials, Dr Rossi is currently focusing her energy on twodimensional structures. “2-d materials are the first step towards more complex structures. The idea is that they are easier to produce and to understand than 3-d materials,” she says.
Funded by the Netherlands Organisation for Scientific Research • https://www.nwo.nl/en/funding/ourfunding-instruments/nwo/innovationalresearch-incentives-scheme/veni/index.html
Stefano Sacanna group Molecular Design Institute Department of Chemistry New York University
Project Coordinator, Professor Laura Rossi Delft University of Technology Van der Maasweg 9, Room D2.180 2629HZ Delft the Netherlands T: +31 30 253 3406 E: L.Rossi@tudelft.nl W: http://www.mycolloids.com/research.html
Colloidal particles The focus in research is on using colloidal particles to develop such 2-d structures, work which is built on continued investigation into their properties and the way they interact with each other. The size of the particles is an important attribute in this respect. “We use particles which are big enough that we can image them with simple optical techniques like light microscopy, while they are also small enough that, under certain aspects, they interact in the same way as atoms and molecules,” explains Dr Rossi. It is possible to image these particles at a high degree of precision, from which researchers can gain new insights into how they assemble. “As the particles themselves are relatively large, we can image them while the process happens, and that’s very important,” stresses Dr Rossi. “By imaging single particles, while the process is happening, we can learn more about how it happens.” This research also holds important implications in terms of the wider goal of preparing the colloidal particles so that they assemble themselves in particular ways. The various different materials that are present in nature are created using building blocks that interact through very specific and directional interactions. “We’re looking
Colloidal cubes with a definite dipole moment spontaneously form large 2D ordered structures useful, for instance, to study defect dynamics.
at using magnetic interactions to provide directional attachments between colloids,” says Dr Rossi. The use of magnetism in this respect is not entirely straightforward; Dr Rossi and her colleagues are looking to build on existing foundations in this area. “The idea is to use what we already know about physics to create a new colloidal building block that
colloidal particles. “Colloidal particles have been used to model atomic and molecular systems, but it’s usually been in recording somewhat simpler systems, like glasses or simple crystals, and only in recent years have more complex colloidal structures started appearing,” she explains. The aim is to achieve a high level of specificity, where the
The idea is to use what we already know about physics to create a new colloidal building block that helps us
design new materials.
helps us design new materials,” she outlines. “Ultimately, what we want to have is a programmeable building block.” From this point, researchers could then look to use these building blocks in the development of 2-d materials with specific geometries, such as graphene for instance, a material that has generated a lot of interest due to its unique electrical, optical, thermal and mechanical properties. The important point in this respect is programmability, yet Dr Rossi says this is very hard to obtain in
colloids behave in exactly the desired way. “In situations when we have a specific geometry in mind, we need to be able to reverseengineer the building blocks to obtain that specific geometry,” continues Dr Rossi. The way that magnetic colloids interact with each other is very different from other colloids, which is why it’s very important to understand the fundamental nature of these interactions. Researchers are looking to put magnets onto the colloids in specific locations, aiming to create a
Model of a 2D network predicted to arise from colloidal particles having 3 magnetic patches.
certain structure. “If you locate these tiny magnets into the colloids, in a very specific pattern, then you can create the structure that you want,” outlines Dr Rossi. One of the structures Dr Rossi and her colleagues are targetting is that of graphene. “The carbon atoms in graphene are arranged in a honeycomb lattice,” she says. “You can imagine having the same architecture, where carbon atoms are replaced by colloids. This is quite difficult to obtain, because the interactions between colloids must be precisely engineered.” A second structure that Dr Rossi is targeting is more amorphous, in that it is not a periodic structure. A high level of control over the properties of the colloids is required in order to form these structures, and Dr Rossi says that results so far are promising. “We see that with magnetic interactions between the colloidal particles, we can make certain structures. We can obtain structures that can be tuned, and can be programmed in a way – this is a first step towards programmable structures,” she outlines. Dr Rossi and her colleagues have found that it
is possible to re-configure certain structures using magnetic building blocks. “Not only can you make structures, but you can also change them by applying for instance an external magnetic field – and the particle will respond to this external field,” she says. “We can think of moving from a structure with a specific property to a structure with a completely different property, by applying some external stimuli or cues.” This feature plays an important role, for instance, in the development of re-configurable materials. The next step could be to build further on these initial findings and look towards more complex structures, with the eventual objective of moving towards 3-d structures and designing materials with specific mechanical or optical properties. This holds important implications for the future of materials development. “We want to understand how we can tune the interactions of the colloids so that we can change the properties of a material. That’s looking towards the future, when we have a higher level of control over these structures,” says Dr Rossi.
L. Rossi, J.G. Donaldson, J.-M. Meijer, A. V. Petukhov, D. Kleckner, S.S. Kantorovich, W. T. M. Irvine, A. P. Philipse and S. Sacanna Competing anisotropic interactions in dipolar hematite cube assemblies, Soft Matter, 14, 1080-1087 (2018). S. Sacanna, L. Rossi and D. J. Pine Magnetic click colloidal assembly, Journal of the American Chemical Society, 134, 6112-6115 (2012).
Professor Laura Rossi
Dr Laura Rossi is an Assistant Professor in the Advanced Soft Matter Group at TU Delft. Earlier in her career she undertook training at leading soft matter laboratories, including the Center for Soft Matter Research at New York University and the van’t Hoff Laboratory for Physical and Colloid Chemistry at Utrecht University where she received her doctoral degree in 2012.