Unstretched Films Research Articles

Deuteron and Oxygen-17 NMR Studies of Molecular Motion in Methanol-Saturated Nafion Membranes

AbstractDeuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at σ75% and σ100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.

Dopant site sizes and dopant rates of diffusion in low-density polyethylene films with covalently attached pyrenyl groups: fluorescence quenching by a homologous series of N,N-dialkylanilines in unstretched and stretched films

ADVERTISEMENT RETURN TO ISSUEPREVArticleDopant site sizes and dopant rates of diffusion in low-density polyethylene films with covalently attached pyrenyl groups: fluorescence quenching by a homologous series of N,N-dialkylanilines in unstretched and stretched filmsRoseann M. Jenkins, George S. Hammond, and Richard S. WeissCite this: J. Phys. Chem. 1992, 96, 1, 496–502Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/j100180a089RIGHTS & PERMISSIONSArticle Views35Altmetric-Citations26LEARN 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 (865 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Remanent polarization and ferroelectriclike behaviour in acrylonitrile/methylacrylate copolymer films

Dielectric hysteresis loops of electric displacement vs. electric field were measured on stretched and unstretched films of an acrylonitrile/methylacrylate copolymer P(AN-MA) at various temperatures between 20 and 90°C and field amplitudes up to 150 MVm-1. The maximum remanent polarization estimated from the loops amounts to 35 mCm-2. A linear relation between piezoelectric d31-coefficient and remanent polarization holds. These findings point to an existing ferroelectric component as one part of the total polarization in P(AN-MA). In general, the main part results from frozen-in dipoles aligned during the foregoing poling procedure. The time stability of total polarization is relatively low, with the ferroelectric contribution being the most stable one.

A high-resolution solid-state 13C NMR study on conformation and molecular motion of low-sulfur keratin protein films obtained from wool

13C high-resolution solid-state NMR spectra of S-carboxymethyl kerateine film obtained from wool (SCMKA) were measured under unstretched and stretched conditions. In the unstretched SCMKA film, the observed 13C chemical shift values and the lineshapes for all the carbons in the spectrum at 100°C are close to those at room temperature, although the molecular motions of the side-chain carbons are different from each other. On the other hand, the lineshapes for the main-chain carbons in the stretched films are significantly changed, although the 13C spin-lattice relaxation times and dipolar-dephasing times for all the carbons are almost unchanged by stretching until 300%. From the spectrum simulation of the C α methine carbons using the conformation-dependent 13C chemical shifts of homopolypeptides as reference data, the appearance of the β-sheet form by stretching was recognized.

Enhancement of the electrical conductivity of polypyrrole film by stretching: Influence of the polymerization conditions

The structure and properties of polypyrrole films prepared by the potentiostatic method (PSM) have been compared to those prepared by the galvanostatic method (GSM). The films contained PF 6 − as the counter ion. Irrespective of the method used, the conductivity of the unstretched films increased as the preparation temperature decreased. The conductivity of the stretched films prepared by PSM increased monotonically with decreasing temperature, while the films prepared by GSM showed a maximum conductivity at −30 °C. The films prepared by PSM gave higher elongation and conductivity than those prepared by GSM. The film prepared by PSM at −40 °C could be stretched up to 2.7 times its original length and the stretched film showed a conductivity of 3.0 × 10 3 S/cm in the stretch direction. The structure of the films was determined by Raman spectroscopy, ESR spectroscopy, X-ray diffractometry and scanning electron microscopy.

Explanation of orientation patterns determined for sheet materials by means of microwaves

Unstretched, biaxially stretched, and uniaxially stretched poly(ethylene terephthalate) (PET) films showed different types of three-dimensional pattern, i.e., the frequency and angular dependencies of transmitted microwave intensity. The resonance frequency and the intensity at the resonance frequency for the biaxially and uniaxially stretched PET films changed with rotation angle, while those for the unstretched PET films stayed unchanged. Thus these properties reflected the dielectric anisotropy of the polymer films. The angular dependence of transmitted microwave intensity at a fixed frequency, i.e., the orientation pattern, gave an orientation angle and a maximum-to-minimum ratio of transmitted microwave intensity. The orientation pattern can be obtained by cutting the three-dimensional pattern at the fixed frequency. This frequency should be selected above the resonance frequency, where the transmitted microwave intensity is one-half that at the resonance frequency in the resonance curve which is located at the low-frequency side. The fixed frequency so chosen is most appropriate, since the maximum-to-minimum ratio and the orientation angle are most sensitive around it. The molecules in polymer films are arrayed on an average in the direction specified by the orientation angle where the transmitted microwave intensity is the smallest because of the shift of the resonance curve to the low-frequency side. The orientation pattern reflecting the dielectric anisotropy is very convenient for determining the orientation of molecules or fibers quickly and nondestructively.

POLARIZED TIME‐RESOLVED FLUORESCENCE SPECTRA OF PHYCOBILISOMES ISOLATED FROM Tolypothrix tenuis EMBEDDED IN POLY(VINYL ALCOHOL) FILM

Abstract–Time‐resolved fluorescence spectra in the ps time range were measured on phycobilisome (PBS) embedded in poly(vinyl alcohol) films. The cyanobacterium Tolypothrix tenuis was used as a source of PBS because the pigment composition and the structure of the PBS are well defined. Isotropic PBS in the unstretched film and PBS uniaxially oriented in the stretched film were investigated. Diameters of PBS hemidiscs were oriented parallel to the film‐stretching direction. The time‐resolved fluorescence spectra of the unstretched sample and of the two polarized components in the stretched samples showed several differences in the rise and decay. The delay time, estimated from the time span between the maximum laser pulse and maximal intensity of the phycocyanin and allophycocyanin fluorescence, was much longer than that reported in the aqueous media. This suggests occurrence of a higher thermal deactivation of PBS in polymer film than in aqueous media. The excitation energy transfer from excited phycocrythrin to allophycocyanin was more efficient in the unstretched than in the stretched samples, and it was greater in the parallel polarized component of the stretched sample than in the perpendicular component. The present results are in agreement with a previous suggestion which states that there are two independent pathways of excitation energy transfer in PBS and that there is more than one final emitter of fluorescence. The molecules taking part in various pathways of energy transfer differ in their orientation within PBS.

Electrical conduction in acrylonitrile/methylacrylate copolymer films

Electrical conduction phenomena on unstretched and stretched films of an acrylonitrile/methylacrylate copolymer were studied by isothermal and thermally stimulated charge decay measurements after corona charging in a wide range of field strengths and temperatures, including the glass transition temperature. In addition, current measurements on two-sided metallised samples at electric fields of 3*106 to 5*107 V m-1 were carried out. The isothermal surface potential decay rates as well as the current-voltage characteristics show ohmic behaviour at low fields indicating intrinsic carriers. For fields higher than approximately=4*107 V m-1 the injection dominates. From the surface potential decay curves a trap modulated effective mobility mu of approximately=7*10-15 m2 V-1 s-1 at T=70 degrees C and a field strength E0=8*107 V m-1 was estimated, which is independent of polarity. A broad open-circuit TSC peak at approximately 80 degrees C is related to the conductivity. An anomalous current peak at about 40 degrees C appears only after being charged for a long time at room temperature (RT) or after freezing in the high-temperature polarisation; it is associated with dipoles. All the electrical properties are almost unaffected by sample stretching.

Effect of crystallinity on charge storage in polypropylene and polyethylene

The improvement of charge storage with annealing, the use of different cooling rates, and stretching in polypropylene (PP) and polyethylene (PE) is discussed. In annealed PP and PE storage increases linearly with both crystallinity and crystallite size. The half-value charge decay temperature can be used as a measure of the latter parameters. Annealing and cooling rate affect the rate of crystalline growth. Changes occur in the physical and/or chemical nature, the concentration of defects in the crystalline region, and the concentration of traps at chain fold-amorphous interfaces. Annealing 4:1 stretched PP film at 140 degrees C gives a half-value charge decay temperature of 152 degrees C, approximately=70 degrees C higher than that for unannealed, unstretched film. Stretching increases amorphous content creating new boundaries, decreases crystallite size, and creates defect traps. >

Small‐angle x‐ray scattering studies of fibrin film: Comparisons of fine and coarse films prepared with thrombin and ancrod

Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 A. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 A. In unstretched fine films, only the 77-80 A spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 A reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 A spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results.

Determination of transition moment directions in molecules of low symmetry using polarized fluorescence. II. Applications to pyranine, perylene, and DPH

The application of angle-resolved fluorescence depolarization techniques to the simultaneous determination of the directions of the transition moments and orientational order of dye molecules incorporated into uniaxially stretched polymer films is discussed and illustrated. The directions of the transition moments of pyranine molecules are determined in a general way, on exciting the molecules in two distinct electronic transitions and monitoring the fluorescence emission under the same conditions. This assumes that the fluorescence emission occurs via the same transition moment for every excited absorption band. Experiments on perylene molecules show that the directions of the transition moments can also be determined from measurements utilizing a single electronic absorption band. In this case the orientational distribution of the molecules is assumed to have the form given by the maximum entropy method. Finally, it is shown the directions of the transition moments of DPH molecules in unstretched polymer films can be determined with this technique. It appears that these molecules are oriented to a very small, yet measurable, extent in unstretched films.

Piezoelectric activity in a copolymer of acrylonitrile and methylacrylate

Results of investigations of piezoelectric properties in a copolymer of acrylonitrile and methylacrylate are summarized. A preliminary explanation is given of the observed phenomena on the basis of surface potential measurements. The maximum values of piezoelectric strain coefficient d/sub 31/ obtained after optimizing the poling conditions for stretched and unstretched films were around 3 and 0.85 pC/N, respectively. The time stability of piezoelectricity was found to be relatively low. A hysteresis loop of electric displacement versus electric field was observed and assumed to be a manifestation of a ferroelectriclike behavior. All the observations point to a dipolar nature of piezoelectricity where ferroelectric and frozen-in dipole orientations obviously superimpose. >

Piezoelectricity in acrylonitrile/methylacrylate copolymer

Abstract The piezoelectric strain coefficient d31 of stretched and unstretched acrylonitrile/methylacrylate copolymer films has been investigated as a function of poling conditions. The maximum d31 values obtained for stretched and unstretched films were around 3 and 0.85 pC/N, respectively.

Piezoelectricity in acrylonitrile/methylacrylate copolymer

The piezoelectric strain coefficient d13 of stretched and unstretched acrylonitrile/methylacrylate copolymer films has been investigated as a function of poling conditions. The maximtun d31 values obtained for stretched and unstretched films were around 3 and 0.85 pC/N, respectively. The time stability of piezoelectricity is relatively low.

Polarized spectra of a series of stilbazolium merocyanines in polyvinyl alcohol films

Polarized absorption, fluorescence and photoacoustic spectra of a series of stilbazolium merocyanines in stretched and unstretched polyvinylalcohol films were measured. Protonated dyes and free based are present in PVA films. The degree of orientation of the dye molecules depends on the substituents present in the molecule. The bulky t-butyl causes a decrease in the degree of orientation and prevents the formation of ground state complexes. In the excited state, the steric hindrance is less important and exciplexes are formed. Only ground state complexes and exciplexes fluoresce. The excitation of monomers is followed by effective thermal deactivation. Ground state complexes and exciplexes have different geometries. Axial deformation of PVA films favours excimer formation, but causes a partial dissociation of the ground state complexes.

Brillouin scattering of oriented films of poly(vinylidene fluoride) and poly(vinylidene fluoride) ‐poly( methyl methacrylate) blends

AbstractTemperature dependent Brillouin scattering studies of PVF2 films stretched to various stretch ratios have been carried out. Elastic constants for unstretched and stretched films have been obtained as functions of temperature. The elastic constant C33 of the stretched films has a greater temperature dependence than that of unstretched films. To elucidate the effect of the surrounding amorphous matrix on the Brillouin spectrum of semicrystalline PVF2 film, we carried out Brillouin scattering studies of films made from blends of PVF2 and PMMA.

Surface potential decay in stretched and unstretched PVDF films

The surface potential decay characteristics of corona-charged stretched and unstretched PVDF films have been investigated as a function of time, thickness, initial surface potential, and voltage polarity. An attempt is made to explain the results on the basis of trapping of charges in the bulk of the material. It is assumed that the charge deposited from corona is trapped in the surface states and is subsequently thermally injected into the bulk.

Conformational defects in Durham polyacetylene

Polyacetylene prepared by the Durham precursor route can be obtained in a disordered form by thermal conversion of a solution-cast film of the precursor polymer, or in a highly oriented form by stretching the precursor film during the transformation reaction. The oriented films show the properties that are characteristic of long straight-chain sequences, but the unstretched films show evidence for very short straight-chain lengths, of no more than 20 or 30 carbon atoms. We discuss the dispersion of the resonantly-enhanced Raman modes with excitation energy and show that within the amplitude-mode formalism of Horovitz the defects that terminate the straight sequences in unstretched material do not impose a preferred sense of bond alternation on the chain. Similarly, the defects introduced through chemical doping or photoexcitation show the characteristics of soliton-like states, with a single “mid-gap” electronic absorption feature which is at significantly higher energies than for stretched Durham or Shirakawa polyacetylene. The dopant-induced infra-red modes, however, are similar in frequency to those in stretched Durham and Shirakawa materials.

Conformational defects in Durham-route polyacetylene

Polyacetylene prepared by the Durham precursor route can be obtained either in a poorly-crystalline form by thermal conversion of a precursor film cast from solution onto a substrate, or in a well-aligned and highly crystalline form if a free-standing precursor film is stretched during the transformation reaction. We find that measurements sensitive to the length of defect-free polyene chain show similar ‘long-chain’ characteristics in both stretch-aligned films and in Shirakawa polyacetylene. These include the dispersion of the resonant-Raman spectra with excitation energy and the ESR linewidth for the neutral spin defects present in materials. In contrast, the unstretched films show the properties expected of chains frequently interrupted by defects. We consider that these are mostly chain bends and chain twists, and show that these conformational defects do not break bond-alternation symmetry on the chain and therefore do not prevent the creation of soliton-like defect states during chemical doping. The evidence for this comes from analysis of the dispersion of the resonant-Raman spectra (the dispersion is very weak), and from the optical absorption spectra of doped films. The peak in optical absorption in unstretched films is at 2.3–2.5 eV, and the ‘mid-gap’ absorption is at 1 eV; both these energies are significantly higher than in Shirakawa material.

PHOTO ACOUSTIC SPECTRA OF PHYCOBILIPROTEINS and CHLOROPHYLLIN IN ISOTROPIC and ANISOTROPIC POLYVINYL ALCOHOL FILMS

Abstract— Photoacoustic spectra (PAS) of biliproteins: R‐phycoerythrin (PE) with R‐phycocyanin (PC) admixture in isotropic and anisotropic polyvinyl‐alcohol (PVA) films were measured. The mixtures of biliproteins and chlorophyllin (Chllin) in PVA were also investigated. In order to establish the influence of PVA anisotropy on PAS amplitude, the stretched and unstretched PVA films colored by Congo red were studied. The films with PE and Chllin mixture when illuminated in the region of PE absorption, show higher PAS signals than the films with PE alone. This is explained by the excitation energy transfer from efficiently fluorescent PE to Chllin that has much lower yield of fluorescence. The stretched films always show a higher PAS signal than isotropic films because of the increase in the thermal conductivity of PVA. But normalized PAS of Congo red and Chllin in stretched PVA are similar to those in unstretched films.Pigment molecules oriented parallel to the direction of film stretching have a lower rate of thermal deactivation compared to that of unoriented molecules as has been found by comparing PAS of differently oriented Congo red molecules using photoselection by polarized light. The same result was obtained for various PE chromophores which are differently oriented in anisotropic films.