1,721,047 research outputs found
Preparation of nanofibers with nanoporous crystalline phases by electrospinning
No full textSyndiotactic polystyrene (sPS) nanofibers with a diameter of 230-720 nm have been prepared via electrospinning of chloroform solutions. The as-spun nanofibers are characterized by an s(2/1)2 helical mesomorphic form but sorption-desorption treatments allow the obtaining of nanofibrous mats characterized by the crystalline nanoporous δ-form. Sorption studies of 1,2-dichloroethane (DCE) from 50 ppm aqueous solutions show that DCE sorption in the nanofibrous mats occurs principally in the crystalline cavities of the nanofibers at a fast rate but the DCE equilibrium uptake is lower than for other δ-form morphologies
Photosensitive Polymers Undergoing Photo-Fries reaction: Understanding the Origin of Refractive Index Modulation
No full textUnderstanding the mechanism of refractive index modulation in materials undergoing photo-Fries rearrangement
No full textMolecules and polymers that undergo a photo-Fries rearrangement are studied by using DFT calculation in order to predict the refractive index modulation which accompanies this light induced process. In particular, monomeric units of polystyrene derivatives (such as poly(p-formyloxystyrene) and poly(4-acetoxystyrene))
are considered and the refractive index calculated starting from the molecular polarizability and following the Lorentz–Lorenz approach. The results demonstrate that the conversion of ester groups to ketone/alcohol provides just a small modulation of the refractive index that does not fit the experimental results reported in the literature. A change in material density is therefore considered as main source of the modulation of the refractive index. Theoretical and experimental evidences are reported to support the picture
Refractive index modulation in polymer film doped with diazo Meldrum's acid
Full text linkDiazo Meldrum's acid undergoes a photoreaction induced by UV light and it is used as photosensitizer in photoresists. Upon photoreaction, a change in refractive index occurs, which makes this system interesting for volume holography. We report on the sublimation effect at room temperature and the effect of photoirradiation on the refractive index in thin films of CAB (Cellulose acetate butyrate) doped with different amount of diazo Meldrum's acid. A net modulation of the refractive index of 0.01 is achieved with 40% of doping ratio together with a reduction of the film thickness
Photosensitive polymers undergoing photo-Fries reaction for volume holography: understanding the mechanism of refractive index modulation
No full textPolymers that undergo to photo-Fries reaction show a remarkable modulation of the refractive index that makes them interesting in the field of volume holography. In order to understand the mechanism of the change in the refractive index we performed theoretical calculations (DFT) on model molecules. The results show that the modulation can be ascribed to a change in the polymer density upon photo-reaction whereas the contribution due to a change in molecular polarizability is small. The theoretical conclusions have been supported by experimental results on two polymers: Polyformyloxide styrene (PFS) and polyacetoxystyrene (PAS)
Process optimization for the manufacturing of holographic elements using Darol photopolymer
Full text linkDesign and manufacturing of high efficiency and reliable volume phase holographic optical elements require photosensitive materials where the performances of the device are straightforwardly related to the recording and post process parameters. In this context, Darol®photopolymers are promising materials since the modulation of the refractive index is set during the thermal process that follows the holographic exposure. In the present study, dry Darol®films are thermally processed to determine the optimized conditions to achieve a large modulation of the refractive index together with good optical properties of the hologram (i.e. transparency), flatness and homogeneity. For each condition, volume phase gratings are written and characterized in terms of diffraction efficiency. A threshold temperature of 150 °C is found, and only latent holograms are obtained at lower temperature, as confirmed by thermal characterizations. Moreover, a dependence of the refractive index modulation on the line density and laser intensity is highlighted
Materials for VPHGs: practical considerations in the case of astronomical instrumentation
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Photochromic materials for holography: issues and constraints
No full textPhotochromic materials can find application in holography, thanks to the peculiar possibility to change reversibly their transparency in the visible (amplitude holography) and their refractive index in the near infrared region (phase holography). The main advantages of such materials are rewritability and self-development. A large change of the key property is crucial to obtain efficient devices and some strategies are followed, accordingly. Production of the holograms have open important issues regarding the film thickness and the nonlinear response to light, because of the strong absorption of the writing light by the material. Results related to these topics, mainly focused on diarylethene-based materials, are reported
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