Solid Polymer Solutions Research Articles

P-140: Holograms Recording in AZO Nematic Liquid Crystal and in its Solid Polymer Solutions

Methods of holographical images recording in nematic LC are proposed. Kinetic performances have been investigated for induced phase transition “nematic-isotropic liquid” in the layers of LC-440D, based on a mixture of liquid crystal (LC) azoxy compounds. Different cases of the absorption of polarized or unpolarized radiation were realized. Spectral changes of LC-440D, as well as the influence of activating radiation wavelength (365 and 405 nm) on the change in the transmission of the LC cell (10 µm thick) with rubbed polymer layers as orientants have been measured. At the same time the kinetics of changes in the intensity of light scattering on it in the transparency (λ = 632.8nm) formed by the spatial anisotropy of the diffraction pattern in the cross section of the probe beam was measured. Holograms are recorded in layers of solid mixtures of molecular solutions LC-440D (12 wt. %) of polymetyl metacrylate that were stored in a few hours, whereas in the pure LC-440D they disappeared in a few minutes.

PROCESSES OF EXCITATION RELAXATION IN MOLECULAR SYSTEMS FOR DIFFERENT TEMPERATURES

In the work studying frequency and temperature dependence of quantum output of the methylene blue molecules and rezazurine molecules in the solid polymer solution are carried out. It has been found an empirical dependence for the constant of speed of excitation relaxation on difference between excited states and temperature: exp( ), 0 kT E k k b mn mn ∆ = ⋅ - ⋅ where b= 0,1. Modelling the processes of excitation relaxation allows to show that the experimental results can be described in supposing that not only electron-vibrational states, but interaction of these states with phonons of the solvent matrix participate in forming the UV absorption bands. As a result, it is obtained the theoretical dependence, which adequately describes the experimental results

Random lasing in porous scattering medium

The spectrum behavior evolution and the threshold of random lasing depending on the way of photon walk randomization in an active random medium were investigated. The following three ways of photon walk randomization were implemented: multiple light scattering by corundum and silica particles embedded into a solid polymer solution of dye (astrafloxin), multiple light reflection at sub-millimeter extensive air pores (mean diameter 200 μm) produced in the medium, and the combined action of both these effects. The most effective lasing is observed in the case of an active medium with air pores and scattering particles in the interpore space. Such a combined porous scattering medium acts as a network of dielectric waveguides transmitting effectively the random light. This spatial structure of the random active medium significantly increases the photon path in the medium, thereby promoting photon multiplication due to stimulated emission. In this combined medium the random lasing reveals the narrowest spectrum, the lowest threshold, and the highest density of spectral energy in the spectrum maximum.

Photonics of nanostructured systems based on photochromic spiro compounds

A review of the results of studies on photoinduced aggregation of photochromic spiro compounds of the class of spiropyrans and spirooxazines is presented. The possibility to form aggregates of photoinduced species of various types, in particular, H and J aggregates, in liquid and solid polymer solutions as well as in photochromic polymers, amorphous films, and mono-and polymolecular layers is shown. The main fields of applications of nanostructured photochromic systems are considered.

Multiple Scattering Active Media as Small-Size Frequency Tunable Sources of Stimulated Emission

We investigated the lasing spectra of multiple scattering active media based on solid polymer solutions of rhodamin 6G with embedded scattering silica particles of mean diameter 500nm. Lasing in these samples appears without any cavity and arises even in rather small active volume 0.05*0.5*0.5mm3. In a thick sample positive feedback for lasing is provided mainly by multiple scattering of light. In a thin sample the feedback is provided both by multiple scattering of light on the particles and light reflection from the sample surface. It is found that the lasing spectra peak wavelength can be varied within 13nm by varying sample thickness in a range 0.1 -1.65mm. A method of continuos laser tuning by wedge-like sample shift with respect to the pump beam is proposed. The presented results are aimed at the development of a new type of microlaser.

Anion effect on the electrochemistry of TTF in polymer solvent

Cyclic voltammetry of a solid polymer solution of a tetrathiafulvalene (TTF) derivative showed different behaviours depending on the nature of the electrolyte anion. A lower potential and current peak for the second redox reaction in the presence of perchlorate revealed a specific interaction between this anion and the TTF dication. This effect also indicates a coupling between the physical diffusion and electron self-exchange during the voltammetric scan. No interaction between the TTF dication and triflimide or TFSI-bis (trifluoromethanesulfonyl) imide-anion was observed. This confirms the exceptional softness of this anion and underlines the role that the nature of the electrolyte anion could play on both the ionic and the electronic conductivities of the electrode polymer materials.

Laser-induced reduction of a dye characterised by a high triplet-state yield and dissolved in a polymer

An investigation was made of the photoreduction kinetics of a dye in a solid polymer solution under the influence of laser radiation corresponding to the band of the first singlet — singlet transition. Participation of higher triplet states was considered in a model of the photoreduction of a dye characterised by a high intersystem crossing yield. An analytic solution was obtained for a system of kinetic equations. This solution takes into account the difference between the photoprocess rates. It is shown that a linear dependence of the effective dye-photoreduction rate on the laser radiation intensity can serve as a test of the participation of higher triplet states in the reaction. A comparison of the theoretical and experimental results obtained in the present study is used to determine the ratio of the photoreduction and deactivation rate constants of the higher triplet state of eosin K.

Photoinduced processes in solid polymer solutions of dyes in an interference field of laser radiation

An investigation was made of the relationships governing the photochemical mechanism of formation of light-induced gratings in solid polymer solutions of a dye with a high quantum yield of the triplet states. The combined analysis of the results of real and numerical experiments was made for a solution of eosin K in gelatin. The protonation rate constant of the dye was measured and the dependence of the diffraction efficiency on the duration of irradiation was explained taking diffusion of the dye into account. A method was proposed for determination of the duffusion coefficient in a spatially modified interference field of the laser radiation. The diffusion coefficients were found.

Increasing the destructiveness of pulsating jets by the application of hydrodynamically active substances

We give the results of experimental studies of the destruction of plaster and coal-cement blocks by pulsating jets of water and water solutions of water-soluble solid polymer compounds on a base of polyethylene oxide. It is shown that the use of water-soluble solid polymer solutions as the working fluid in the generator of the pulsating jet leads to an increase in the depth of the holes and grooves by a factor of 1.5–3.5. Three figures. One table.

Picosecond Dynamics of Bragg Grating Formation in the Fulgide E-α-(2,5-Dimethyl-3-furyl)ethylidene(dicyclopropylmethylene)-2,5-furandione

The refractive index change that accompanies the color change in a class of thermally stable and fatigue-free organic photochromic molecules is used to probe the picosecond dynamics of grating growth within a solid polymer solution of the material and in an organic solvent. These studies demonstrate the intrinsic picosecond response time of the fulgide by direct measurement of the refractive index change of the chromophore. Additionally, these dynamical studies allow for the quantification of the cycling potential for the material.

Photochromism of dihydropyridines. Formation and decay of coloured intermediates from 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine on irradiation in chloroform and acetonitrile solutions and in poly(methyl methacrylate) solid solution

The mechanism of the photochromic reaction of 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine was studied by flash photolysis in chloroform and acetonitrile solutions and in solid solutions of poly(methyl methacrylate). Photochromic species with absorption at 330, 375 (shoulder), 410 and 510 nm were detected in chloroform solution immediately after the flash. The bleaching reaction in solution was monomoleculer with a rate constant of approximately 5 × 104 s−1. The reverse reaction in solid polymer solution and in the solid state was characterized by a non-exponential time dependence which could be analysed in terms of a dispersive first-order reaction; the time constants of the process were of the order of several seconds and several hours respectively.

Photochromism of 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine in the solid state: an example of a dispersive chemical reaction

The photochromic behaviour of 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine (DHP) in the solid state is described. The time dependence of the colour decay process is analysed in terms of a dispersive first-order chemical reaction. The non-exponential dependence can be accounted for by a Gaussian distribution of activation energies whose width decreases with increasing temperature. A similar dispersive bleaching reaction with DHP was observed in solid polymer solutions.

Photoaddition of maleic anhydride to unsaturated polymers in homogeneous solution, solid polymer–solution, and solid polymer–vapor systems

AbstractPhotoreactions of maleic anhydride (MAH) with unsaturated olefinic polymers such as 1,2‐polybutadiene, 1,4‐polybutadiene, block copolymer of styrene and butadiene, polystyrene, poly(styrene‐co‐isoprene), and poly(styrene‐alt‐methyl methacrylate) were investigated in air. When the polymers have olefinic unsaturation, the addition of MAH to the polymers in homogeneous solutions proceeded efficiently by a chain mechanism, and the quantum yield of the photoaddition of MAH was greater than unity under irradiation at λ > 310 nm. From the effects of solvent and photosensitizer, a radical chain mechanism involving crosslinking of the polymers by MAH molecules was suggested. Together with the spectroscopic results, the reaction mechanism was discussed. The photoaddition reaction was then applied to the surface photomodification of polymer films. Photoreactions were conducted at the interphase between solid polymer and acetone solution of MAH and also at the interphase between solid polymer and gaseous MAH. Irradiation by a 300‐W high‐pressure mercury lamp could bring about considerable modification of the surface properties of the polymers, which then show improved wettability and dyeability. From the oxygen permeation experiments, the present interfacial phototreatment was shown to provide a double‐layered polymer film in which one side of the film is polar and hydrophilic while the other side is nonpolar and hydrophobic.

The orientation of luminophor molecules in solid polymer solutions

The orientation of luminophor molecules in solid polymer solutions