PMMA colloidal crystals

Figure 6.5 Photos of (a) reaction apparatus and (right) 1 h after white PMMA colloidal for polymerization of MMA, (b) PMMA colloidal crystal solids were placed in the solution, and crystals (white solids) in La(N03)3 + Fe(N03)3 in (c) calcination furnace, ethylene glycol-MeOH solution (left) 20 m...

EG-Methanol solution of metal nitrate infiletrated into PMMA colloidal crystal template... 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

Fig. 8 Left scheme of vertical lifting codeposition of trimodal colloidal particles. Center trimodal colloidal crystal (tCC) consisting of large PS, intermediate PMMA, and small silica particles. Right Top view of binary inverse opal (blO) after PS and PMMA pyrolysis of the tCC in the center [25]...

The materials which have been mentioned here so far are predominantly shaped in planar films of hierarchical order. However, the synthesis of hierarchically structured particles is also highly desirable, as they might be further processed and used for the preparation of composite porous materials. Wu et al. showed the synthesis of raspberry-like hollow silica spheres with a hierarchically structured, porous shell, using individual PS particles as sacrificial template [134]. In another intriguing approach by Li et al. [135], mesoporous cubes and near-spherical particles (Fig. 10) were formed by controlled disassembly of a hierarchically structured colloidal crystal, which itself was fabricated via PMMA latex and nonionic surfactant templating. The two different particle types concurrently generated by this method derive from the shape of the octahedral and tetrahedral voids, which are present in the template crystal with fee lattice symmetry. 

A further advantage of PMMA relies on its availability. Uniformly sized PMMA spheres are prepared by polymerization of methyl methacrylate (MMA) in water. The product of the polymerization then takes the form of a colloidal suspension of solid particles that are so small that they tend not to settle. By centrifugation, the PMMA particles are forced to settle and pack into a solid, often called a colloidal crystal. In such colloidal crystals, the PMMA spheres are arranged in a close-packed fashion in the same manner as the silica spheres that make up natural opal [178]. Therefore, these materials can be referred to as synthetic opals. Several textbooks cover selective aspects of the physicochemical properties of PMMA [181,182]. 

Figure 6.1 SEM images of (a) colloidal crystal (opal structure) of PMMA spheres and (b and c) 3D0M LaFeOa prepared by the colloidal crystal template method.

The sol-gel method was widely used in the preparation of photonic materials and structures during the last decades. The design and preparation of hybrid nanocomposites for photonics are widely described in Refs [7,145-147]. The wide range of photonic structures prepared using the sol-gel method include colloidal crystals based on silica or polystyrene spherical particles [148,149], photonic crystals [150-152], photonic bandgap materials [153-155], and opals based on the deposition of silica, titania, and/or ceria in the voids of an ordered array of PMMA spheres [156]. A more extensive overview of photonic materials by sol-gel method can be found in Chapter 28. 

Colloidal photonic crystals are often synthesized from monodisperse microspheres of PMMA, PS, and silica. The use of functionalized microspheres can increase the performance of certain photonic devices and CCTP has been successful in the synthesis of NC-loaded photonic crystals with a polymerizable macromonomer. Monodisperse microspheres composed of a PS core with a poly(methacrylic acid) (PMAA) shell were synthesized through an emulsion copolymerization of PMAA macromonomers synthesized by CCTP with PS. It was found that the CdZnS NCs capped with PMAA macromonomers could be anchored to the microsphere surface as the PMAA acts as a ligand. These colloidal crystals are then formed into a film, yielding well-ordered, hexagonal close packed structures that show pH-responsive behavior. All films with different hydrodynamic diameters simultaneously exhibit brilliant colors from red to blue, providing a promising avenue for the next generation of photonic devices. 

Most of 3DOM metal oxides are fabricated by an alkoxide-based sol-gel process. The typical procedures include (i) preparation of a colloidal crystal template by ordering monodispersive microspheres (e.g., PS, PMMA or silica) into a face-centered close-packed array (ii) infiltration of a metal alkoxide solution into voids in the colloidal crystals, and in-situ solidification of the precimsor via a sol-gel process and (iii) template removal via a calcination or extraction pathway [99,217-219], Using the alkoxide-based sol-gel method, 3DOM oxides of Si, Ti, Zr, Al, Sb, W, Fe, and 3DOM mixed oxides of some of them can synthesized due to the moderate reactivity of their alkoxide preciuTsors [99], However, most of the other metal alkoxides exhibit high reactivity and their reactions are too quick to be... 

Poon et al. [103] studied a similar system as De Hoog et al. [102], this time with PMMA particles with R = 238 nm and PS polymers with Mp = 370kg/mol. We focus on their experiments carried out at a colloid volume fraction 0.1. Just as De Hoog et al. they observed four regimes. At low concentration a colloidal fluid was observed. Across the phase boundary a narrow concentration regime was found of equilibrium fluid-crystal phase behaviom. 

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