Guest-host composites

After this overview of photonic antenna properties, we now turn to some intriguing optical properties we have recently observed in different dye-zeolite guest-host composites. 

Figure 1. Examples of photorefractive polymer design a) guest/host composite b) fully functionalized side>chain polymer c) fiilly functionalized main chain polymer d) interpenetrated cross-linked polymer network.

This group of nanocomposites has been the first one to be studied because of the very simple sol-gel chemistry involved in the preparation of guest-host composites. The guest organic molecules are dissolved in the precursor sol during the synthesis and at the end of the preparation will result in being incorporated within the oxide network. Several examples have been reported and different matrixes have been used, such as silica (Dai, 1992) or silica-titania. Some alternative routes have been also proposed to improve the... 

Posudievsky, O.Y., Telbiz, G.M., and Rossokhaty, V.K. (2006) Effect of solvent nature on liquid-phase self-assembly of MEH-PPV/MCM-41 guest-host composites. /. Mater. Chem., 16, 2485-2489. 

Depending on conditions, frozen substances in comet nuclei can be crystalline ices, amorphous ices, and clathrate hydrates (compounds in which cages in the water-ice lattice can host guest molecules). Compositions of the ices and associated organic materials in comets have been determined from both telescopic and spacecraft observations. Spectral line measurements of gases in a comet s coma allow the identification of molecules and radicals. An inherent difficulty in spectral measurements is that volatiles in the coma are commonly broken... 

SHG-active guest crystals within the polymer matrix. Unless alignment is achieved, light scattering from the microcrystals (due to disorientation, reflection and refraction) will render the composite useless. In addition, it is very important to maximize the loading degree (i.e. the guest/host ratio), as the total nonlinear response is proportional to the amount of SHG-active material present. Finally,... 

Quinone Compound, Liquid Crystal Composition, and Guest-Host-Type Liquid Crystal Cell Employing the Same T. Katoh, US Patent 6,703,084 (March 9, 2004)... 

Figure 11. Possible relative positions of the energy levels in a typical guest-host photorefractive polymer composite containing PVK, TNF, and an azo-chromophore. A possible sequence of events leading to mobile charge generation is also included.

As discussed earlier, while the scale of the fillers is substantially different, nanocomposite materials concepts and technology are very similar to those of conventional composite materials. This is clearly demonstrated in the case of new thermosets for nonlinear optical (NLO) applications, " " where nanocomposite of liquid crystalline thermosets, IPNs, and simple filled thermosets are evaluated. Tripathy et al. discussed four different ways to prepare nonlinear optical polymers. (1) The polymer matrix is doped with NLO moieties in a guest/host system (2) In side-chain polymer systems, NLO polymers with active moieties are covalently bonded as pendant groups (3) In the main chain polymer, the chromo-phores are incorporated as parts of the main polymer backbone to enhance the temporal stability of the NLO properties and (4) Stability of the optical noninearity in sol-gel-based thermosets is related to... 

The change of guest atom composition in the matrix atom is accompanied by an intercalation reaction within the same crystal structure of the matrix atom. The characteristic feature of intercalation/deintercalation is, first, that the reaction proceeds not only at the interface between electrolyte and host intercalation compound electrode but also even in the interior of the electrode. 

This aspect of polymer-dopant interaction has been the subject of a more detailed study by Chen et al. [104]. PPV-Cs has been compared with rubidium-doped polyacetylene, for which the guest/host size ratio is very nearly the same (Table 1.7). Whereas poly-acetylene-Rb has an intrachannel coherence length of 25 A for the ion sublattice, the coiresponding value is 70 A in the case of PPV-Cs the ion siiblattices are incommensurate for both at the compositions studied. Such intriguing differences can only be understood by considering, in a more polymer-specific manner, the character of the chain and the guest-host interactions. 

Photoactivation of the as-prepared samples of QDs embedded in the above polymers increased their quantum yields, which was attributed to photoinduced surface state passivation, in addition to system relaxation. The resulting polymer-encapsulated QDs systems show an extended photochemical stabihty under continuous illumination in air without any observed blue shift, in contrast to the very short lifetime of the original QD solutions. While such fabricated QD-polymer composites in the initial work appear less sensitive toward hydrocarbon vapor exposures, many optimizations -for example, for the composite guest/host selection and the layer thickness -may be pursued to allow for the making of functional QD/polymer sensing materials based on the developed method. In addition, the encapsulation of QDs with selected monomers via in situ polymerization to make QD-based precursors is a useful technique with which to enhance QD hfe for, potentially, many other applications. 

Given that the FTC already gives a wealth of information on the structure of the host and pore structures, frequently no need for additional information is required. The guest and host compositions should be provided on a per cell basis. For instance, the mineral sodalite can be ideally formulated as lNa8Cl2l[AlgSi6024] — SOD, while the material with a... 

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