Stretched Poly Vinyl Alcohol Research Articles

Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Some optical properties of poly (vinyl alcohol) (PVA) films are investigated prior and after the rubbing and stretching of the samples. Birefringence of the prepared foils is enhanced as their stretching degree and rubbing become larger. These processing factors are also affecting the values of the ordinary and extraordinary refractive indices. The induced anisotropy in PVA foils is evidenced in the morphological characteristics observed by optical microscopy. The spreading and adhesion behaviors of a nematic liquid crystal on PVA foils are analyzed by means of contact angle measurements. Preliminary testing of the nematic on the PVA films revealed significant variations in transmitted light intensity during sample rotation under crossed polarizers. The high contrast between dark and bright patterns is indicative of uniform and homogenous alignment of nematic on the rubbed and stretched PVA foils.

Excitation energy transfer in partly ordered polymer films differing in donor and acceptor transition moments orientation

Based on spectroscopic measurements selected properties of nonradiative Förster energy transport are studied in uniaxially stretched polyvinyl alcohol thin films for three systems differing in donor and acceptor transition moments orientation relative to the axis of stretching. In particular, donor – acceptor emission anisotropy spectra yield completely different regularities for these systems in uniaxially stretched films, whereas they are similar in unstretched films. In particular it is shown that acceptor fluorescence can be either strongly polarized after nonradiative energy transfer in stretched films or depolarized depending on the angular distribution of acceptor transition moments in the matrix. Donor and acceptor emission anisotropy decays exhibit similar regularities to those of steady-state measurements. The obtained results are analyzed with the help of Monte Carlo simulations.

Anisotropic saturable absorption of single wall carbon nanotubes aligned in polyvinyl alcohol

ABSTRACTWe report anisotropic optical absorption and saturable absorption (SA) properties of aligned single wall carbon nanotubes (SWNT) embedded in the mechanically stretched polyvinyl alcohol (PVA) film. Polarized absorption spectra of the film showed a strong anisotropy for the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating the good alignment of the embedded SWNT. The SA property of the band gap transition measured using a polarized femtosecond fiber laser showed a strong polarization angle dependence for the stretched film. When the polarization of light is parallel to the stretching direction, the absorption saturation of the stretched film became more efficient than that of the unstretched film because of the apparently stronger transition moment.

Spectral properties of stilbazolium merocyanines oriented in stretched polymer films and Langmuir–Blodgett monolayers

Three stilbazolium merocyanines: 1-(6′-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine; 1-(11′-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine; 1-(10′-carboxydecyl)-4-[4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine salt HCl located in Langmuir–Blodgett monolayers and deposited on quartz plate as well as embedded in isotropic or stretched polyvinyl alcohol films were investigated. Dyes occur in protonated and free-base forms. The concentration ratio of these forms depends on pH of subphase (for monolayers) or resin addition (in polymer film).The polarized absorption and fluorescence spectra were measured and coefficients of absorption and emission anisotropy were calculated. Dye molecules were in both matrices oriented, but degrees of orientation of various forms of dye were different. The anisotropies of absorption and emission are also different which strongly suggests the occurrence of dye forms with different yield of fluorescence and various orientations. The formation of mixed aggregates of protonated and free-base form is suggested. The orientation of stilbazolium merocyanines in anisotropic matrix is important in the application of these dyes as the sensors for measurements of the local electric field in biological membranes as well as for the formation polarizing absorption polymer film used in some types of two-colours liquid crystal displays.

Polarized Photoacoustic Spectra of the Cyanobacterium Synechococcus Oriented in Polymer Film

Photoacoustic spectra (PAS) were obtained for the cyanobacterium Synechococcus (Anacystis nidulans) cells embedded in isotropic and stretched polyvinyl alcohol films. The polarized radiation with the electric vector changing in 30° intervals with respect to given direction in a sample plane was used. Two cyanobacterium strains, one with very low biliprotein content, second with normal amount of biliproteins were investigated. The polarized absorption and fluorescence spectra were also measured. Conclusions were drawn about the thermal deactivation occurring in differently oriented pools of chromophores and about mutual orientation of their transition moments. Thermal deactivation in carotenoids (Cars) of both strains was different. The ratio of Car thermal deactivation to the thermal deactivation of chlorophyll (Chl) was higher in cyanobacteria with lower content of biliproteins than in the strain with normal amount of these complexes. Hence biliproteins can play the role in excitation energy transfer from Cars to Chls. For complex biological samples, polarized PAS can be a more sensitive method to investigate the directions of the absorption transition moments than the widely used polarized absorption spectra.

Orientational Ordering of Bipolar Nematic Droplets in a Stretched PVA Matrix

Abstract The structural modifications and orientational ordering of nematic (SCB) droplets with the bipolar director-field configuration, embedded in a uniaxially stretched polyvinyl alcohol (PVA) matrix, are studied using polarized optical microscopy. It has been found that the unidirectional ordering of droplets with stretching takes place in two stages. At small matrix deformations, each bipolar structure is captured by the surface of the droplet cavity, so that the bipolar axis makes an angle with the long axis of the cavity and therewith is gradually rotated toward the stretch direction in accordance with the affine transformation of matrix dimensions. As the droplet non-sphericity further increases, there comes a point where the elastic deformation energy of the captured structure overcomes the surface interactions and, as a result, the droplet abruptly reorients parallel to the long cavity axis. The measurements of the orientational distribution function have testified the pronounced threshold natu...

Incorporation of stilbazolium merocyanines into resting and stimulated mononuclear leukocytes.

Stimulated and resting mononuclear leukocytes were incubated with a stilbazolium merocyanine dye 1-(6'-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5- dienylidene)ethylidene]-1,4-dihydropyridine and immobilized in isotropic and stretched polyvinyl alcohol film. Polarized absorption, fluorescence and fluorescence excitation spectra were collected and the anisotropy of absorption and emission were calculated. Analysis of the spectra pointed to: i. the occurrence of perturbation of the membrane structure by incubation with the dye, and ii. influence of the blood serum addition, during the process of incubation with the dye, on the efficiency of incorporation of merocyanine into the cells and the degree of the dye orientation in the membrane. A small fraction of the dye molecules introduced into resting cells was found oriented to a higher degree than a large fraction incorporated into stimulated cells. The incubation time longer than 15 min caused strong changes in the membrane structure both of the resting and stimulated cells.

Distribution of energy absorbed by purple bacteria between various paths of de-excitation

Polarized absorption, photoacoustic and fluorescence spectra of cells of the purple bacterium Rhodospirillum rubrum, embedded in isotropic and stretched polyvinyl alcohol films, were measured at 296 and 85 K. The existence of pools of bacteriochlorophyll molecules, characterized by various absorption and emission maxima and different orientations of their transition moments vdth respect to the membrane plane, was shown. The polarized spectra suggest that in addition to the light-harvesting LH1 B875 complexes, other antenna complexes (B806 and complexes absorbing in the long-wavelength region) are present in Rhodospirillum rubrum. The ratio between the yield of fluorescence polarized parallel and perpendicular to the direction of the electric vector of the exciting light (376 nm) and the film axis is about 1.8 for bacteriochlorophyll emission at 892 nm and about 0.14 for that at 928 nm. In the parallel component, 28% of the energy absorbed in the near-IR bands of bacteriochlorophyll is converted into heat and 72% is used for fluorescence emission and photochemistry, whereas in the perpendicular component, the corresponding values are about 60% and 40% respectively. We conclude that the mutually parallel bacteriochlorophyll antenna chromophores lose less energy by thermal dissipation than chromophores with a lower degree of orientation. This suggests a very efficient trapping in the reaction centres of that part of the excitation energy which migrates between chromophores having mutually parallel transition moments.

Orientation of Dye Molecules in Skew Stretched Polyvinyl Alcohol Film

Abstract The mutual orientation of pigments in living organisms, for example the antenna pigments in photosynthetizing Organisms, have strong influence on molecular processes such as excitation energy transfer which are closely related to physiological function of photosynthetizing apparatus of plants, algae and bacteria [l].

Vanadyl ethylenediamine tetraacetate in stretched polyvinyl alcohol films. Determination of orientation distribution by EPR spectroscopy

The EPR spectrum of vanadyl ethylediamine tetraacetate complex (VO-EDTA) dissolved in polyvinyl alcohol (PVA) films has been investigated as a function of the film stretching. The orientation of the VO-EDTA complex relative to the stretching direction was determined from the fitting of the experimental data to Ohno's theory for semi-ordered systems, modified to take into account the low symmetry of the VO-EDTA complex.

Polarized photoacoustic, absorption and fluorescence spectra of chloroplasts and thylakoids oriented in polyvinyl alcohol films

The polarized photoacoustic, absorption and fluorescence spectra of chloroplasts and thylakoids in unstretched and stretched polyvinyl alcohol films were measured. The intensity ratios of fluorescence bands at 674 nm, 700 nm, 730 nm and 750 nm, and the polarized fluorescence excitation spectra are strongly dependent on light polarization and film stretching. In stretched films, thylakoids exhibit predominantly 674 nm emission. The ratio of photoacoustic signal to absorption is different for light polarized parallel and perpendicular to film stretching. This difference is large in the region of chlorophyll a and carotenoids absorption in which the fluorescence excitation spectra are also strongly dependent on light polarization and film stretching. The observed spectral changes are explained by reorientation of pigment molecules influencing the yield of excitation transfer between different pigments.

Linear dichroism of cyanine dyes in stretched polyvinyl alcohol films: a physical chemistry laboratory experiment

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGet e-AlertsLinear dichroism of cyanine dyes in stretched polyvinyl alcohol films: a physical chemistry laboratory experimentL. V. Natarajan , Margaret Robinson , and Robert E. Blankenship Cite this: J. Chem. Educ. 1983, 60, 3, 241Publication Date (Print):March 1, 1983Publication History Received3 August 2009Published online1 March 1983Published inissue 1 March 1983https://doi.org/10.1021/ed060p241© American Chemical Society and Division of Chemical Education, Inc.RIGHTS & PERMISSIONSArticle Views302Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-AlertsGet e-Alerts Journal of Chemical Education Get e-Alerts

Polarized Absorption and Emission of Chlorophyllin, Phycoerythrobilin and Phycocyanobilin in Stretched Polyvinyl Alcohol Films

Polarized Absorption and Emission of Chlorophyllin, Phycoerythrobilin and Phycocyanobilin in Stretched Polyvinyl Alcohol Films

Orientation of the hemes of high potential cytochromes relative to photosynthetic membranes, as shown by the linear dichroism of oriented preparations

The orientations of high potential cytochromes with respect to photosynthetic membranes was investigated in spinach chloroplasts and in Rhodopseudomonas viridis. The general approach consists in detection with polarized light of photoinduced absorbance changes related to the oxidation of the cytochromes. The orientation of cytochrome c-558 was measured at room temperature in chromatophores and whole cells of Rps. viridis, oriented on glass slides and in a magnetic field, respectively. The orientation of cytochrome b-559 of green plants was detected at 77 K in magnetically oriented chloroplasts. In both cases the dichroic ratio for the α band shows that the heme plane makes an angle greater than 35°C with the membrane plane. Moreover, the dichroic ratio is not constant throughout the α and β bands, for both cytochrome c-558 and b-559. Linear dichroism spectra of oriented pure horse heart cytochrome c and cytochrome c 2 of Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films show that the variations of the dichroic ratio in the α and β bands can be explained by the occurrence of x- and y-polarized transitions absorbing at slightly different wavelengths.

Linear dichroism of microalgae, developing thylakoids and isolated pigment-protein complexes in stretched poly (vinyl alcohol) films at 77 K

A variety of unicellular algae, thylakoids from higher plants in different stages of maturity and isolated pigment-protein complexes were oriented in stretched polyvinyl alcohol films. Low temperature linear dichroism (LD) spectra of Chlorella pyrenoidosa and higher plant thylakoids in the films were very similar to those obtained after orientation of similar samples using magnetic or electric fields. Positive LD bands corresponding to Chl a (670) and (682) and negative bands due to Chl a (658) and Chl b (648) were resolved in spectra of the light harvesting Chl a/b protein. Chl b (648) and Chl a (658) and (670) were not seen in the LD spectrum of thylakoids from plants grown in intermittent light, the Chl b-less mutant of barley, Euglena gracilis or the cyanobacteria, Phormidium luridum and Anacystis nidulans, but did appear upon chloroplast maturation in Romaine lettuce and during the greening of etiolated and intermittent light plants. The highly oriented long wavelength Chl a (682) in the light-harvesting complex may represent residual PS II whose peak dichroism is centered at 681 nm. The PS I preparation had a Chl a b ratio of approx. 6 and the LD spectrum was positive with a maximum at 690–694 nm and a band of lower amplitude at 652 nm. The minor LD band was not observed in PS I preparations from organisms that lack Chl b such as the cyanobacteria, intermittent light plants and the Chl b-less mutant of barley. We suggest that the 652 nm band is due to Chl b molecules associated with the antenna of PS I and are distinct from those on the light harvesting complex whose orientation is different. We also conclude that all the Chl a forms are oriented and that the long geometric axes of the pigment-protein complexes, as deduced from the configuration they assume in the stretched films, are axes that normally lie parallel to the plane of the native thylakoid.

Electron spin resonance of the phosphorescent triplet states of p-phenylphenol and p-phenylphenolate ion in stretched polyvinyl alcohol films

Using a stretched polyvinyl alcohol film as a host, electron spin resonance (ESR) of the phosphorescent triplet states of p-phenylphenol and p-phenylphenolate ion has been studied by changing the pH of the medium as an example of the application of ESR to an acid-base equilibrium. In assigning ESR spectra of aromatic acid and conjugated base, the present method is demonstrated to be most convenient and useful.

Electron spin resonance of bis-acetylacetonatocopper(II) and bis-salycylal-1,2-ethylenediiminatocopper(II) in stretched polyvinyl alcohol films

Using stretched polyvinyl alcohol film as a host, electron spin resonance has been studied for bis-acetylacetonatocopper(II) and bis-salycylal-1,2-ethylenediiminatocopper(II) as planar transition metal complexes. The usefulness of the present method in application to such complexes is demonstrated, especially for the assignment of anisotropic terms of g and hyperfine structures.

Linear dichroism of light harvesting bacteriochlorophyll proteins from Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films

Light-harvesting bacteriochlorophyll-protein complexes from Rhodopseudomonas sphaeroides 2.4.1 and R-26 mutant are solubilized in sodium dodecyl sulfate and imbedded in polyvinyl alcohol. Stretching induces orientation, and the linear dichroism of visible and near infrared absorption is analyzed. Based on a simple model, angles between the particle axis and the transition dipole moments are found. In the near infrared absorption band of the R-26 light-harvesting protein the dichroic ratio varies from 1.30 to 1.57. Using the absorption curves the band is resolved into two exciton components. In the visible absorption band the dichroic ratio has a constant value of 0.43 for the R-26 protein but varies with wavelength for the wild type light-harvesting protein. This variation is attributed to an additional bacteriochlorophyll not present in the R-26 protein.

Polarized absorption and ESR spectra of acridine C-radical

The polarized absorption and ESR spectra of the acridine C-radical have been measured at room temperature, the radical was produced at 77 K by γ-ray irradiation of a stretched polyvinyl alcohol film saturated with acridine. The dichroism of the absorption spectrum has been well explained by the results of MO calculations for the acridine C-radical.

Photomechanical effects in photochromic systems

Abstract