From all type of external stimuli the light rays are most commonly used because it involves only photochemical
processes easily to control. One of the most studied of photochemical processes is photoisomerization groups, in
particular the azobenzene groups. The azobenzene and his derivatives, known for Z(sin)-E(anti) reversible
photoisomerization properties, have been extensively used as functional groups to synthesize various
photosensitive compounds.
The UV irradiation at different time of modified maleic anhydride - styrene copolymers with azo dye solutions
were with UV light to increase the rate of Z(sin)-E(anti) isomerisation. The changes in the spectral absorption
domain for azo compounds, a decrease in optic absorbance after irradiation, with a predisposition to come back at
primary value was made with SECOMAMS750 UV–Vis spectrophotometer.
We describe the electro-optical behavior of polymer stabilized liquid crystal (PSLCs)
networks used for the development of electrically variable focus lenses. We start with a short review of
mechanisms influencing the performance of those lenses, including the most important one : the light
scattering. Then the role of the polymer chain morphology in electrically controllable molecular
reorientation and formation of orientation defects in PSLCs is investigated. We use two non mesogene
monomers, with respectively one and two functionalities, to create two different degrees of cross-linking in
PSLCs. By using optical polarimetry and scattering experiments, we investigate the defect formation in
those PSLCs, outline the presence of 3D orientational defects and show that the PSLCs with higher crosslinking
demonstrate better electro-optical reversibility.
We report the synthesis of five new hybrid polymeric structures obtained by free radical copolymerization of
some organic azo-based methacrylate monomers and 3-methacryloxypropyl trimethoxysilane (MEMO). The copolymers
are soluble in common solvents like methylene chloride, chloroform, dichlorbenzene, dimethylsulfoxide,
dimethylformamide. The copolymeric structures might be interesting from the point of view of nonlinear optical
response due to a rich content in chromophoric units determined by
H-NMR spectroscopy. The structures were also
characterized by FT-IR spectroscopy, TGA and SEC analysis.
In the large family of polymers, the azobenzene derivatives represent one fascinating materials class, along with
stylbene and azomethinic derivatives. This interest is explained by combination of the properties of anisotropy with the
photoinduced behaviors. The photoinduced birefringence, relief grating, the high optical nonlinearity resulted from the
sin-anti isomerism, molecular reorientation, the exceptional stability to writing and erasing by laser radiation, are just the
most important arguments for their usage of these polymeric architectures in the NLO field as: LCD, chemical sensing,
devices for storage and transmission of information .
This presentation covers the development and characterization a new series of materials from viewpoint of:
-Modification of the polymer materials by the chemical transformation of the "common" polymer support an
underlining: photorefractivity, NLO properties
-Utilization of these polymers as components in guest-host materials preparation.
The reversible photoisomerization and thermal isomerization of azobenzene-based groups covalently bound to the polymers systems were investigated in the solution. The thermal Z-E isomerization rate could be obtained by varying the substituent of azobenzene or copolymer composition. This change of orientation of azobenzene groups may be suitable for optical storage. In principle the orientation change is permanent, but it can be easily erased by heating, on which the original random orientation is largely restored.
We prepared a copolymer of the maleic anhydride with styrene, to which a colored structure designated for the functionalization was added. The new polymer was used to prepare reverse-mode PDLC films. Reverse-mode PDLC are designed for applications where it is important that the failure of the device is a transparent state, rather than a scattering one. We obtained reverse-mode PDLC using a nematic liquid crystal with negative anisotropy (Delta) (epsilon) <0, LCM 3141 (NIOPIK), and we measured the optical transmission of the film. The system was switched from OFF-transparent state to the ON-scattering one, by a sufficiently small voltage, but with a rather low contrast ratio.
During the last decade the interest in polymeric material for second-order nonlinear optical properties has been constantly growing. They combine structural electronic properties, with good thermal and mechanical stability, a relatively low cost and easy processability. The second order nonlinear optical (NLO) properties of such materials have electronic origin, with an ultra-fast response time. In the present paper, we report the preparation and characterization of a new material with a higher concentration of a NLO chromophore. We have synthesized a new dye monomer by the phase transfer catalyzed reaction. We have prepared the copolymer with styrene, by bulk copolymerization; the initiator was di-t-butyl peroxide at 120 degrees C. We have characterized the monomer and the copolymer by IR; UV-Vis; H-NMR spectroscopy. The glass transition temperature and the melting point have been obtained using the differential scanning calorimetry. For studying the NLO properties, the samples have been poled by the Corona poling method, in an electric field of approximately 100V/micrometers . We have appreciated the second- order nonlinear coefficient by comparing the light signal passing through the sample, with the signal passing through a standard quartz plate.
We have synthesized two chromophore monomers, starting from chloromethyl styrene and methyl methacrylate, and the corresponding homopolymer and copolymer. The obtained structures have been characterized by UV-Vis, IR and H-RNM. The molar fraction of the chromophore monomers in copolymers have been determined by H-RNM and elementary analysis. We have measured the NLO third order coefficients by the degenerated four wave mixing method and high values have been obtained.
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