Self-Assembly of Polyhedral Hybrid Colloidal Particles
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Self-Assembly of Polyhedral Hybrid Colloidal Particles Adeline Perro1, Etienne Duguet3, Serge Ravaine4 and Vinothan N. Manoharan1,2 1
School of Engineering and Applied Sciences, Harvard University, Cambridge MA 02138, USA, 2 Department of Physics, Harvard University, Cambridge MA 02138, USA, 3 CNRS, Université de Bordeaux, ICMCB, Pessac, France, 4 CNRS, Université de Bordeaux, CRPP, Pessac, France. ABSTRACT We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra, and more. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensional space. We present some preliminary studies on the self-assembly of these complex shaped systems based on electron and optical microscopy.
INTRODUCTION Non-spherical colloids are potential precursors for new materials such as 3D photonic crystals with a band gap in the visible spectrum. Here we describe a seeded emulsion polymerization technique to create such particles. The main advantage of this technique over other techniques that use emulsion droplets as templates [1] is that it is allows for a much higher yield of specific types of clusters. Also, we show that it is possible to create some colloidal particles composed of crosslinked polymer that can be index matched in an appropriate solvent. Moreover, studying the crystallization of these colloids could yield insights into new methods of making photonic crystals. EXPERIMENTAL DETAILS Materials. Tetraethoxysilane (TEOS, 99%, Sigma), styrene (99%, Alfa Aesar), ethylene glycol dimethacrylate (EGDMA, TLC), sodium persulfate (98%, Sigma), and ammonia (25% in water, SDS) were purchased as reagent grade and used without further purification. Methyl methacrylate (MMA, 99%, Alfa Aesar) was purified by distillation before use. Methacryloxymethyltriethoxysilane (MMS) were purchased from Gelest, the surfactant Synperonic NP30 from Fluka and Norland 68 optical adhesive from Norland. Water was Milli-Q grade (Millipore). Synthetic Procedures. Silica seeds were synthesized using a procedure described elsewhere.[2] To favor the growth of the polymer beads onto the mineral surface, silica particles were surfaced modified by adding MMS at a concentration that yielded 1 functional group per nm2. 50 mL of surface modified silica suspension were introduced in a three-neck round flask of 250 mL
equipped with a chilled condenser. The mixture was stirred at 300 rpm under nitrogen for 2 hours. 150 mg of surfactant (Synperonic NP30), 5 g of monomer (styrene or MMA + EGDMA (15 % w/w)) were then introduced. The mixture was heated at 70°C before the introduction of
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