2014, Murray, Eoin, Born, Philip, Weber, Anika, Kraus, Tobias

Traditionally, organosilica nanoparticles have been prepared inside micelles with an external silica shell for mechanical support. Here, we compare these hybrid core–shell particles with organosilica particles that are robust enough to be produced both inside micelles and alone in a sol–gel process. These particles form from octadecyltrimethoxy silane as silica source either in microemulsions, resulting in water-dispersible particles with a hydrophobic core, or precipitate from an aqueous mixture to form particles with both hydrophobic core and surface. We examine size and morphology of the particles by dynamic light scattering and transmission electron microscopy and show that the particles consist of Si–O–Si networks pervaded by alkyl chains using nuclear magnetic resonance, infrared spectroscopy, and thermogravimetric analysis.

2014, Born, Philip, Schön, Volker, Blum, Susanne, Gerstner, Dominik, Huber, Patrick, Kraus, Tobias

Alkylthiol-coated gold nanoparticles spontaneously segregate from dispersion in toluene to the toluene-vapor interface. We show that surface tension drops during segregation with a rate that depends on particle concentration. Mono- and multilayers of particles form depending on particle concentration, time, and temperature. X-ray reflectometry indicates fast monolayer formation and slow multilayer formation. A model that combines diffusion-limited segregation driven by surface energy and heterogeneous agglomeration driven by dispersive van der Waals particle interactions is proposed to describe film formation.

2012, Born, Philip

Colloidal crystals can exhibit novel properties arising from the combination of particle properties and collective phenomena of particle packings. Particular colloidal crystals composed of nanoparticles are interesting, because of the unique properties of nanoscale objects, and because of the formation of three-dimensional structures on scales that can be manufactured using established methods only with great technical effort. The aim of this work was to develop appropriate ways to produce the crystals. Two approaches were chosen. In the first approach, colloid particles were deposited on surfaces in a process similar to dip coating. Large-area crystalline particle films with low defect density were obtained by an optimized deposition geometry. In the second approach attractive interactions between particles were used. Reducing the thermal energy induced agglomeration of the particles. This approach allowed production of a variety of particle structures. Besides the expected result, formation of hexagonal particle packings, unexpected results were obtained. In the first approach a superposition of two crystallization mechanisms ensured a robust formation of hexagonal particle packings. In the second approach crystallization among the particles was suppressed in a pure thermally induced agglomeration.