Advanced Functional Materials

Cover image for Vol. 27 Issue 31

Cover Picture: TiO2 Nanoparticle–Photopolymer Composites for Volume Holographic Recording (Adv. Funct. Mater. 10/2005)

15_10/2005TiO2 nanoparticle–photopolymer composites have been employed for volume holographic recording, as reported by Sánchez and co-workers on p. 1623. Photoinduced segregation of the high refractive index, grafted nanoparticles between polymer-rich areas leads to improved refractive-index modulation amplitudes with respect to the base material without nanoparticles. The cover schematically shows a holographic grating registered in this nanocomposite material. These nanocomposite materials should enable the production of holographic optical elements to efficiently control light with angle and wavelength selectivity. This could be used, for example, in liquid-crystal display technology.

A new and efficient photopolymer for the recording of volume holograms is presented. The material comprises a mixture of UV-sensitive acrylates and grafted titanium dioxide nanoparticles with an average size of 4 nm. We report the formation of holographic gratings with refractive-index modulation amplitudes of up to 15.5 × 10–3—an improvement of more than a factor of four over the base material without nanoparticles—while maintaining a low level of scattering and a high transparency in the visible-wavelength range. The influence of the composition of the acrylate system on the final properties of the holographic material is also investigated and discussed. The presence of multifunctional monomers favors the compositional segregation of the different components, while the addition of monofunctional acrylate, highly compatible with the grafting of the nanoparticles, favors the dilution of these nanoparticles.

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