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Hierarchical Self Assembly of Colloids: Control and Manipulation from Nano-Granular

Final Report Summary - HIERARSACOL (Hierarchical Self Assembly of Colloids: Control and Manipulation from Nano-Granular)

It is hard to overstate the importance that the ability by mankind to manipulate the properties of materials had and still has on our society (e.g. bronze age, iron age, industrial revolution started after the creation of steel). In this project the main aim was to develop methodology, mostly through self-assembly SA investigated quantitatively in real-space, to arrive at materials for which the structure can be manipulated at multiple length scales from atomic, to nano, micro and granular length scales. The main route for the hierarchical SA was the use of well-designed chemically synthesized nanoscale colloidal building blocks combined with emulsion droplets that were composed of dispersions of these nanoparticles NPs or mixtures thereof. By letting these droplets dry slowly (still dispersed in the second solvent) the NPs were made to self-assemble into regular crystalline arrangements. This SA process turned out to be influenced in interesting ways by the spherical confinement it took place in. For instance, in the case of hard-spheres it was very surprising to find out that a so-called icosahedral crystal would form as the most stable phase when roughly 100.000 particles are present or less before the bulk stable close-packed face centered cubic phase becomes stable again. This example is of interest to both fundamental science, but also to applications of supraparticles SPs. As one example: if SPs are made from larger particles with a size of several hundred nm such SPs would display omnidirectional structural colors could be an sustainable alternative form of paints which are traditionally based on the absorption of light instead of interference. In subsequent-projects we also investigated SPs SA-ed from plate-like particles, cube-shaped, triangular-shaped particles and several binary systems (one of them forming a so-called Laves crystal phase). Amazingly, in the case of the binary structures the spherical confinement was found to affect much less influence on the crystals formed. To analyze all these structures and their defects/deviations from bulk phases quantitatively in real-space new particle fitting routines were developed that have been (rods) or are in the process of being made available freely to the scientific community. These routines can be equally used for the analysis of 3D electron microscopy tomography data sets as well as for 3D light nanoscopy (stimulated emission depletion) confocal microscopy data as well. Not only were new methods developed to analyze the structures formed, new synthesis protocols were also realized for instance to make anisotropic particles, with new properties. Examples of this are noble metal rod-like NPs composed of fully alloyed combinations of Au, Ag, Pt and Pd. These out-of-equilibrium particle shapes were realized by performing their core-shell synthesis and subsequent alloying inside a mesoporous silica shell. The combination of alloying and the anisotropic shape gives these rods new plasmonic and catalytic properties that were further enhanced by SA inside SPs into particles with smectic-like ordering. The SPs realized from the many different types of NPs are not only interesting to catalysis, sensing, as calibration standards (an application that is likely to be developed into a prototype for commercial use), they are also interesting in lighting. We also developed a versatile methodology to arrest the SA of both nano and larger colloidal particles by using mixtures of different kind of solvents and a monomer that can be polymerized under the influence of a high intensity light pulse within a second time scale. This methodology allows not only to investigate colloidal structures and processes in new ways (by ‘stopping time’) the resulting arrested structures could also be manipulated by external electric fields. Already the methodologies for SA in a spherical confinement and the real space analysis of complex shaped particles has found use not only in other projects in our group, but have already been applied by other groups as well. It is expected that a while after the closing of this project the results will have been published in > 40 papers, many in high impact journals.