A facile and flexible synthesis for colloidal molecules with well-controlled shape and tunable patchiness is presented. Cross-linked polystyrene spheres with a liquid protrusion were found to assemble into colloidal molecules by coalescence of the liquid protrusions. Similarly, cross-linked poly(methyl methacrylate) particles carrying a wetting layer assembled into colloidal molecules by coalescence of the wetting layer. Driven by surface energy, a liquid droplet on which the solid spheres are attached is formed. Subsequent polymerization of the liquid yields a wide variety of colloidal molecules as well as colloidosomes with tunable patchiness. Precise control over the topology of the particles has been achieved by changing the amount and nature of the swelling monomer as well as the wetting angle between the liquid and the seed particles. The overall cluster size can be controlled by the seed size as well as the swelling ratio. Use of different swelling monomers and/or particles allows for chemical diversity of the patches and the center. For low swelling ratios assemblies of small numbers of seeds resemble clusters that minimize the second moment of the mass distribution. Assemblies comprised of a large number of colloids are similar to colloidosomes exhibiting elastic strain relief by scar formation.

We present the synthesis of new shapes of colloidal silica particles by manipulating their chemical composition and subsequent etching. Segments of silica rods, prepared by the ammonia catalyzed hydrolysis and condensation of tetraethylorthosilicate (TEOS) from polyvinylpyrrolidone loaded water droplets, were grown under different conditions. Upon decreasing temperature, delaying ethanol addition, or increasing monomer concentration, the rate of dissolution of the silica segment subsequently formed decreased. A watery solution of NaOH (∼mM) selectively etched these segments. Further tuning the conditions resulted in rod–cone or cone–cone shapes. Deliberately modulating the composition along the particle’s length by delayed addition of (3-aminopropyl)-triethoxysilane (APTES) also allowed us to change the composition stepwise. The faster etching of this coupling agent in neutral conditions or HF afforded an even larger variety of particle morphologies while in addition changing the chemical functionality. A comparable step in composition was applied to silica spheres. Biamine functional groups used in a similar way as APTES caused a charge inversion during the growth, causing dumbbells and higher order aggregates to form. These particles etched more slowly at the neck, resulting in a biconcave silica ring sandwiched between two silica spheres, which could be separated by specifically etching the functionalized layer using HF.

The hydration reaction of MgO to amorphous Mg(OH) 2 is a model hydration reaction and is important to diverse research fields, ranging from catalysis to Earth Sciences. Although the bulk thermodynamics and surface energies of these phases are well studied,[1,2] real time and real space analysis of the reaction at ambient pressure is lacking. In this study, the hydration of MgO nanocrystals is studied at the single particle level, both in real space and in diffraction space using in‐situ Transmission Electron Microscopy (TEM) at near‐ambient pressure and temperature. Upon exposure to water vapor and the electron beam, the MgO nanocrystals react with H 2 O and convert to amorphous Mg(OH) 2 . Real‐time recordings of the hydration reaction reveal that the reaction starts at the MgO nanocrystal surface and proceeds inwards at a constant rate while the Mg(OH) 2 shell expands outwards. The growth rate is found to be constant throughout the reaction. Furthermore, as the applied dose rate is increased, the growth rate increases accordingly. Possible mechanisms for the beam‐promoted transformation are discussed, including the role of defect formation and migration at the interior and at the surface of the MgO nanocrystals, H 2 O diffusion towards the MgO surface, and the possible influence of beam‐generated H 2 O dissociation products. Assemblies of converting MgO/Mg(OH) 2 nanocrystals exhibited a reorganization of the assembly framework due to the solid volume increase (~100%) of each individual nanocrystal.