Effectiveness of organic sunscreens is limited by phototoxicity and degradation. Both of which can be significantly reduced by encapsulation in hollow particles or covalent incorporation into the solid structure of particles, but direct comparisons of the two methods have not been reported. In this study, physical encapsulation and covalent incorporation of sunscreens were compared with 1 mol % salicylate and curcumeroid sunscreens. 2-Ethylhexyl salicylate was physically encapsulated in hollow silica nanoparticles prepared by oil-in-water (O/W) microemulsion polymerizations (E-Sal). Some of these particles were coated with an additional shell or cap of silica to reduce leaking of sunscreen (cap-E-Sal). Covalent incorporation involved co-polymerizing tetraethoxysilane (TEOS) with 0.2 mol % of new salicylate and curcuminoid sunscreen monomers with triethoxsilyl groups. Particles were prepared with the salicylate attached to the silica matrix through single silsesquioxane groups (pendant; P-Sal) and two silsesquioxane groups (bridged; B-Sal). Particles based on a new curcuminoid-bridged monomer were also prepared (B-Curc). Sunscreen leaching, photodegradation, and sunscreen performance were determined for the E-Sal, cap-E-Sal, P-Sal, B-Sal, and B-Curc particles. Covalent attachment, particularly with bridged sunscreen monomers, reduced leaching and photodegradation over physical encapsulation, even with capping.

We describe the formation of efficient transmission diffraction gratings created from patterned high quality ligand-capped CdSe nanocrystals (NCs), using a facile microcontact molding procedure. Soft polymer replicas of commercially available master gratings were "inked" with solvated NCs and the resulting pattern transferred to a variety of substrates after drying. Large-area (>0.5 cm(2)), defect free diffraction gratings were prepared with a variety of submicrometer line spacings and feature sizes down to ca. 160 nm. The morphology of the resulting pattern was tuned by controlling the concentration of the NC-based ink. Optimized gratings (1200 g/mm) showed an increase in transmission diffraction efficiency (DE) with increasing nanocrystal diameter. DE = ca. 15% (488 nm) for 2.5 nm diameter NCs versus DE = ca. 25-30% (488 nm) for 7.3 nm nanocrystals. These increases in DE are ascribed to changes in both the real (n) and imaginary (k) components of the complex index of refraction as NC diameter increases. We demonstrate the ability to in- and out-couple incident laser radiation into internal reflection elements using these stamped NC gratings, including single-mode waveguides, offering a novel application of ordered nanocrystal thin films.

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Hybrid organicinorganic materials provide the opportunity for combining organic chromophores into inorganic networks. The resulting hybrids can be used for numerous optical, biomedical and nanotechnology applications. Hybrid organicinorganic particles that absorb and fluoresce in visible or ultraviolet light are particularly useful for bio-imaging, sensors, and as a safe sunscreen. The organic component can be incorporated through physical entrapment or through covalent incorporation through siloxane linkages. By containment in the hybrid material, the performance lifetime of the chromophore can be extended significantly and environmental contamination by its leaching out can be reduced. In this study, silica particles containing 1 mol % dimethylaminonathyl-sulfonamide (dansyl) dyes were prepared by three different methods: 1) physical encapsulation inside a hollow silica particle, 2) covalent attachment of pendant chromophores through a single silyl group and 3) covalent attachment through two silyl groups. The influence of the mode of entrapment on the particles' spectroscopic properties, the propensity of the chromophores to leach from the particles, and photochemical degradation of chromophores were determined for the three classes of hybrid materials.