Efficient materials for recording volume holograms are described that could potentially find application in archival data storage. These materials are prepared by mixing photopolymerizable vinyl monomers with a liquid epoxy resin and an amine hardener. A solid matrix is formed in situ as the epoxy cures at room temperature. The unreacted vinyl monomers are subsequently photopolymerized during hologram recording. A key feature of these materials is the separation of the epoxy and vinyl polymerizations. This separation allows for a large index contrast to be developed in holograms when components are optimized. The standard material described in this work consists of a low index matrix (n = 1.46), comprised of diethylenetriamine and 1,4-butanediol diglycidyl ether, and a high index photopolymer mixture (n = 1.60) of N-vinylcarbazole and N-vinyl-2-pyrrolidinone. This material is functional in thick formats (several millimeters), which enables narrow angular bandwidth and high diffraction efficiency. A dynamic range (M/#) up to 13 has been measured in these materials. Holographic performance is highly dependent on the amount of amine hardener used, as well as on photopolymer shrinkage.

A large absorption resonance has been observed in the far-infrared spectrum of water confined within inverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in heptane. The amplitude and spectral position of this resonance depend on the size of the water pool. The origin of the THz absorption of these liquid pools is assigned to surface oscillations of the water pool, driven by the interfacial tension of the water−surfactant-oil interface. These data indicate a dramatic restructuring of the density of states of the liquid and are consistent with a theoretical model for the oscillatory modes of liquid droplets. The presence of a large excess in the vibrational density of states of confined water could have far-ranging implications in many biochemical and chemical processes where confined water is present.

The far-infrared absorption spectrum of nanometer-sized water pools at the core of AOT micelles exhibits a pronounced resonance which is absent in bulk water. The amplitude and spectral position of this resonance are sensitive to the size of the confined water core. This resonance results from size-dependent modifications in the vibrational density of states, and thus has far-reaching implications for chemical processes which involve water sequestered within small cavities. These data represent the first study of the terahertz dielectric properties of confined liquids.

An important issue in developing applications for photopolymers in holography is the effect of film thickness on recording properties. Now it is possible to create these samples with a much wider range of thickness (d = 20-1400 mum) than was previously available. We exploit these recent advances in photopolymer processing to systematically evaluate how the dynamic range of a photopolymer depends on its thickness. The results illustrate that sample performance increases linearly with thickness as predicted by standard models of volume holography. However, above a critical thickness sample performance degrades, and the angular response of recorded plane-wave holograms shows evidence of grating curvature. These distortions are likely the result of photopolymer shrinkage, which in thicker samples occurs in a nonuniform fashion. This problem limits the performance of these photopolymers and is likely to be an issue for any photopolymer that undergoes comparable polymerization shrinkage.

Nanoscale TiO 2 was dispersed in a solution of dichloromethane and methanol for deposition on the surface of acrylic sheets. After evaporation of the solvent, the TiO 2 was adhered firmly to the acrylic surface. This deposition method yielded uniform, high surface area coatings as evidenced by scanning electron micrographs. The TiO 2 films deposited on acrylic in this manner have superior durability when compared to TiO 2 deposited on glass supports. The TiO 2 fused on the acrylic surface manifests a comparable photocatalytic activity to TiO 2 deposited directly on glass and a markedly higher activity than TiO 2 deposited on glass with a poly-(vinyl alcohol) binder. A photocatalytic reactor was constructed from the TiO 2 -acrylic composite materials, and the applicability of this deposition technique was demonstrated by the 97% degradation of methyl orange in 2.0 L of a 13 ppm solution after 500 min of photoexposure.