Polymer Opals

Another nice example of nanostructuring an MIP layer is the work published by Wu et al. [138, 139] who developed a label-free optical sensor based on molecularly imprinted photonic polymers. Photonic crystals were prepared by self-assembly of silica nanospheres. The space between the spheres was then filled with MIP precursor solution. After polymerization, the silica was dissolved, leaving an MIP in the form of a 3D-ordered interconnected macroporous inverse polymer opal (Fig. 15). The authors were able to detect traces of the herbicide atrazine at low concentrations in aqueous solution [139]. Analyte adsorption into the binding sites resulted in a change in Bragg diffraction of the polymer characterized by a color modification (Fig. 15). 

Romanov, S., Maka, T., Torres, C. et al.. Emission properties of dye-polymer-opal photonic crystals, J. Lightwave TechnoL, 17, 2121, 1999. 

Similarly to the codeposition procedure above, the metal can also be delivered as nanoparticles to the colloidal crystal template, but in this case after preparation of the template. This was demonstrated for gold nanoparticles, which were filled into the interstitial sites of a polymer opal by filtering a gold nanoparticle suspension through the preassembled opal with a filter small enough to hold back the nanoparticles [33]. The templating opal was prepared before in very much the same way by filtration of a PS latex suspension. 

Romanov SG, Maka T, Sotomayor Torres CM, Miiller M, Zentel R (1999) Photonic band-gap effects upon the light emission from a dye-polymer-opal composite. Appl Phys Lett 75 1057... 

Pursiainen OLJ, Baumberg JJ, Winkler H, Viel B, Spahn P, Ruhl T (2008) Shear-induced organization in flexible polymer opals. Adv Mater 20 1484—1487... 

Diffraction of light in photonic crystals has also been used to enhance the photo-luminescent properties of fluorophores (17,99], and by loading the interstitial voids of polymer opals with highly fluorescent dyes, stimulated emission can be enhanced [134,135]. For more complex opal structures the dye must be loaded into the colloid matrix by using water-soluble dyes [136] or by modified emulsion polymerization reactions for non-water soluble dyes (137, 138]. 

Egen, M. and Zentel, R. (2004) Surfactant-free emulsion polymerization of various methacrylates towards monodisperse colloids for polymer opals. Macromol. Chem. Phys., 205 (11), 1479-1488. 

An interesting variation on template deposition is to self-assanble ordered nanostructures (e.g., surfactants) and microstructures (e.g., polystyrene or Si02 beads) on the surface of an electrode and then electrodeposit into the self-assembled pores. The order in the resulting nanostructure is imposed by the self-assembled layer, not by the substrate. Schwartz and coworkers have extended this idea to the use of crystalline protein masks to produce ordered nanostructures of metals (such as Ni, Pt, Pd, and Co) and metal oxides (such as Cu20). Braun and coworkers have used the electrodeposition of materials into self-assembled colloidal crystals or silica or polymer opals. The template is then removed (see Figure 17.11) to produce an inverse opal. This type of templating produces periodic microstructures that can be used to produce functional photonics. Figure 17.11 shows the production of CdSe and Ni inverse opals by electrodeposition into a colloidal crystal with subsequent removal of the colloidal crystal template. ... 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

T. Ruhl, P. Spahn, G.P. Hellmann, Polymer 44,7625 (2003) (Artifical opals prepared by melt compression see Example 3-43)... 

The easiest way to calibrate a light scattering photometer is to use a suitable standard as a reference. Although polymer solutions and dispersions of colloidal silica have been used for this purpose, commercial photometers are equipped with opal glass reference standards. 

Figure 15.7 (a) The preparation of inverse opal photonic balls using polymer spheres and an inorganic... 

F. Caruso uses monodisperse polymer spheres and their colloidal crystals only as templates to create hollow capsules or extended opal arrays with the layer-by-layer technique. Again this is a typical colloid chemistry tool which is unparalleled in low molecular weight organic chemistry, and hollow mesostruc-tures systems with astonishingly high complexity and chemical function can be generated. 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

The opals obtained by self-assembly are mechanically unstable because there is only Van der Waals force between spheres. The subsequent infiltration process could easily destroy the ordered colloid arrays. So we annealed the opals of polymer sphere to increase their stability. As a result, there would form interconnections between spheres, which come from the slight melting of the sphere surfoces. These necks can provide the opal with necessary mechanical stability. In addition, they are important for producing inverse opal structure. After infiltration, when the samples are treated with calcinations, these necks can act as channels for the transport of the products formed during calcination like CO2. 

Yoshino, K., Satoh, S., Shimoda, Y. et al.. Tunable optical properties of conducting polymers infiltrated in synthetic opal as photonic crystal, Synthet. Met., 121, 1459, 2001. 

Yoshino, K., Tatsuhara, S., Kawagishi, Y. et al.. Amplified spontaneous emission and lasing in conducting polymers and fluorescent dyes in opals as photonic crystals, Appl. Phys. Lett., 74, 2590, 1999. 

Cassagneau, T., and Caruso, E., Semiconducting polymer inverse opals prepared by electropolymerization, Adv. Mater., 14, 34, 2002. 

Ozaki, M., Shimoda, Y, Kasano, M. et al.. Electric field tuning of the stop band in a liquid-crystal-infiltrated polymer inverse opal, Adv. Mater., 14, 514, 2002. 

Xu, T., Cheng, Z., Zhang, Q. et al.. Fabrication and characterization of three-dimensional periodic ferroelectric polymer-silica opal composites and inverse opals, J. Appl. Phys., 88, 405, 2000. 

Silicon is extremely important as a building block of unicellular algae -diatoms. The main building material of the frustule (the finely sculptured protective surface layer of diatoms) is a float-stone, an opal-like water-containing polymer of silica Diatoms are the only group of organisms whose development is totally dependent on the presence of soluble forms of silica in the environment. When silicon sources run out, DNA replication stops. 

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