Oriented Polymer Films Research Articles

Electronic Excitation Energy Migration in Partly Ordered Polymeric Films

Multistep intermolecular energy migration between elongated fluorophores (carbocyanines) in uniaxially oriented polymer films is studied based on fluorescence depolarization and Monte-Carlo simulations. Contrary to disordered systems it is found experimentally that the concentration depolarization of fluorescence in uniaxially oriented films is extremely weak despite effective energy migration. Based on the concentration depolarization experiment in the ordered matrix it is possible to estimate the angle between absorption and fluorescence transition moments of carbocyanines. The values of that angle are very close to those obtained from other methods.

Excitation energy migration in uniaxially oriented polymer films: A comparison between strongly and weakly organized systems

The mechanism of multistep excitation energy migration in uniaxially oriented polymer films is discussed for strongly and weakly orientating dyes in poly(vinyl alcohol) matrix. The comparison between both types of systems is based on concentration depolarization of fluorescence, Monte-Carlo simulations and linear dichroism data. It is found that the alignment of transition dipole moments of fluorophores in the ordered matrix relative to the direction of polymer stretching exhibits strong effect on the concentration depolarization of fluorescence. In ordered matrices of flavomononucleotide and rhodamine 6G concentration depolarization of fluorescence remains quite strong, whereas for linear carbocyanines it is very weak despite effective energy migration.

P-171: Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.

Device application of oriented polymer films fabricated by friction transfer

Device application of oriented polymer films fabricated by friction transfer

A review of modeling approaches for oriented semi-crystalline polymers

Modeling changes in the physical properties of oriented semi-crystalline polymer films is beneficial for understanding the fundamentals associated with structure property relationships and could be used for developing new polymer films with significantly enhanced physical properties. Relating the molecular changes observed in oriented polymer films to inherent polymer characteristics provides valuable insight for the development of new polymers which exhibit enhanced physical properties upon orientation. Modeling efforts will be reviewed that have attempted to use fiber composite theory to explain the transitions seen during the orientation process.

The effect of intermolecular donor–acceptor energy transfer on emission anisotropy in uniaxially oriented polymer films

Excitation energy transport between donors and acceptors is studied for uniaxially stretched and unstretched poly(vinyl) alcohol films. Donor emission anisotropy courses versus acceptor concentration as well as donor–acceptor emission anisotropy spectra occurred quite different in stretched and unstretched films. Upon donor excitation the total emission anisotropy rapidly decreases when passing from the donor to the acceptor fluorescence band in disordered systems. However, such a pronounced effect has not been found in partly ordered films. Donors and acceptors exhibit highly preferential mutual orientation in strongly ordered films resulting in the preservation of acceptor emission anisotropy.

Optical-strain characteristics of anisotropic polymer films fabricated from a liquid crystal diacrylate

The optomechanical characteristics of oriented polymer films made from a photopolymerizable liquid crystal diacrylate (BASF LC242) were examined, with general implications for oriented films of similar materials being used and considered for display-component applications. The birefringence of these uniaxial films before and after polymerization was determined by measuring the retardation between crossed polarizers, (resulting in Δn=0.142±0.002 at 633 nm for the cured polymer films). Optical-strain characteristics were also determined by measuring the transmittance of the films between crossed polarizers at two wavelengths (612 and 633 nm) during the application of a monotonically increasing tensile strain. Under the conservative assumption that Poisson’s ratio is constant for the relatively small strains in our experiment, we develop a strained-waveplate model to detect changes in birefringence directly from the modulation in transmittance with increasing strain. We show that strain applied along the axis of the polymer chains did not substantially affect the birefringence, and strain applied perpendicularly caused only a slight decrease (∼1% decrease for 10% strain). These results highlight the robustness of fully polymerized reactive mesogen optical films to withstand the moderate strains anticipated during manufacturing processes and in-service deformation caused by bending or impact.

Monte-Carlo Simulation of Energy Migration in Uniaxially Oriented Polymer Films

Nonradiative electronic energy migration between identical fluorophores is studied numerically in uniaxially oriented polymer films. The reorientation effect of dipole moments induced by film stretching leads to extremely different concentration- and time-courses of emission anisotropy compared to those in disordered system. In particular, the effect of a much weaker concentration depolarization of fluorescence is due to the fact that not only primarily excited molecules contribute to emission anisotropy in oriented films.

Thermal and mechanical properties of high Tc bulk superconductors and their applications

The Iwate CREATE (Collaboration of Regional Entities for the Advancement of Technological Excellence) Project, “Advanced Applications of Magnetic Field”, started since October 1999, aims a creation of a COE and a new industrial area in the field of magnetic field applications and magnetic measurements. The basic study group in this project is making extensive measurements on mechanical properties (strength, toughness and so on) and thermal properties (thermal conductivity, thermal diffusivity, Seebeck effect, and so on) of melt-textured high T c bulk superconductors in order to build up a database and feed it back to the higher performance bulk material processing technique in the future. This group also studies the magnetizing technique for these materials and realization of various magnetic field environment for the application to the magnetic separation, highly oriented polymer film and so on.

Excitation energy migration in uniaxially oriented polymer films

Multistep nonradiative excitation energy transport is for the first time studied in uniaxially stretched polymer films. Concentration depolarization studies performed for 3,3 ′-diethylthiacarbocyanine iodide (DTCI) for stretched (system I) and unstretched (system II) polyvinyl alcohol films (PVA) yield extremely different results. As expected, disordered system II exhibits strong concentration depolarization due to energy migration between identical fluorophores. However, for stretched films, concentration depolarization effect is much weaker and it occurs at higher dye concentrations compared to system II. This fact is mostly due to strongly modified angular distribution of dipole moments of molecules taking part in the excitation energy migration.

Dispersion of Birefringence and its Influence on On-Line Measurement of Stresses in Polymer Films

Birefringence distribution in biaxially oriented polymer films is often used to assess non-uniformities in processing and in physical properties. Off-line characterization of this property can be performed by direct measurement of anisotropy in the refractive index, a process that is slow and not suitable for on-line use. By comparison, the spectral contents analysis (SCA) method is fast and easily adaptable for on-line process monitoring and real-time process control. However, implementation of this method requires accurate knowledge of the chromatic dispersion of birefringence. This paper discusses the contribution of birefringence dispersion to the precision of birefringence measurements by the SCA method, and it describes a new spectrometric procedure for accurate measurement of this material property.

Solid-State Replication of Relief Structures in Semicrystalline Polymers

The use of semicrystalline polymers for surface structuring allows multiple embossing and structuring of oriented polymer films, in contrast to amorphous polymers. The Figure shows an oriented perfluorinated polymer film (FEP), on which a lamellar grating has been superimposed by solid-state embossing. Polarized optical microscopy reveals the combined optical effects of surface structure and molecular orientation.

Solid-State Replication of Relief Structures in Semicrystalline Polymers

The use of semicrystalline polymers for surface structuring allows multiple embossing and structuring of oriented polymer films, in contrast to amorphous polymers. The Figure shows an oriented perfluorinated polymer film (FEP), on which a lamellar grating has been superimposed by solid-state embossing. Polarized optical microscopy reveals the combined optical effects of surface structure and molecular orientation.

Effect of structure on the deformation and failure of oriented polymer films

This study compares the effect of anisotropic structure on the room temperature (23°C) deformation and failure behavior of two distinctly different polymers. One a single phase nematic polymer, PMDA-ODA polyimide [PI] with a glass transition, T g , near 400°C; the other a previously studied anisotropic two phase molecular polymer composite, isotactic polypropylene [IPP] with a glass transition near 14°C. Although isotactic polypropylene has a two phase crystal-noncrystalline structure its deformation behavior is controlled by the noncrystalline phase. A series of oriented PMDA-ODA polyimide [PI] films are fabricated and their orientation characterized. The present study investigates whether the deformation and failure behavior of these anisotropic single phase nematic PMDA-ODA polyimide films (tested at a very low strain rate at room temperature) is similar to that previously observed for isotactic polypropylene at its low strain rate failure envelope limit.

A comparison of the crystallization behavior of HDPE on oriented iPP and sPP substrates

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic or/and syndiotactic polypropylene (iPP or/and sPP) substrates at various conditions was studied by means of transmission electron microscopy and electron diffraction. The results indicate that HDPE crystals always grow epitaxially on the iPP substrates under the conditions performed, while on the oriented sPP substrate epitaxially grown HDPE can only be observed when quenching the HDPE-melt directly to room temperature. The reason for this phenomenon results from the thinner lamellae of sPP compared to iPP, and consequently smaller critical nucleus size of HDPE is required for the occurrence of its epitaxial crystallization on the sPP substrate. It is further found that the melt-drawn oriented polymer films are ideal substrates for conducting comparative studies of polymer hetero and graphoepitaxy. By comparing the hetero and graphoepitaxies of HDPE–iPP and HDPE–sPP systems, it is concluded that the heteroepitaxial interaction between polymers is stronger than their graphoepitaxial counterpart. Therefore, heteroepitaxy of polymers takes place prior to their graphoepitaxy

Orientation induced chromism in poly(methylhexysilane)

The orientation-induced conformational transition was studied on thin films of poly(methylhexylsilane) (PMHS). The orientation behavior of molecular chains was analyzed by the inclination-angle-dependence of the polarized UV spectrum and the FTIR reflection–absorption spectroscopy (RAS). The changes in conformation of PMHS chains were monitored with the UV absorption spectrum. It was shown that the structure of the spin-cast film depended upon the thickness of films. In thick film (408nm), molecular chains are not oriented, and favor the disordered conformation, which shows absorption band at 300nm. In contrast, extended conformation with trans-rich segments is produced in addition to the disordered conformation in thin spin-cast films (45–100nm). The extended conformation gives rise to a sharp absorption band at 338nm. The molecular chains with extended conformation are oriented parallel to the substrate surface. The uniaxially oriented films were prepared by drawing the film on supporting polymeric substrates and by crystallization on highly oriented polymer films. As the degree of orientation is increased, the 338nm band increases in intensity relative to the 300nm band. The 338nm band dominated the UV spectrum of the highly oriented PMHS film instead of the 300nm band. A conformational transition to the extended conformation from disordered state is induced by the molecular orientation, exhibiting a drastic spectral change in the UV spectrum.

A continuum approach to electrorheology

An equilibrium thermodynamic approach is employed to derive a continuum-level expression for the electric field-induced stress in uniaxial anisotropic materials. Although this model is developed specifically to describe electrorheological and electrostrictive behavior of suspensions, it also applies to other uniaxial materials such as nonpolar nematic liquid crystals, biaxially oriented polymer films, and paper. This model introduces new electrostriction coefficients, which are material parameters that describe the strain dependence of the dielectric tensor as well as the field-induced stresses. An experimental technique for measuring the electrostriction parameters is outlined. An idealized microscopic model is presented to illustrate the relationships between microscopic parameters and the macroscopic electrostriction coefficients. The model is used to determine the stresses in common applications; predictions from the continuum approach agree with direct calculations from a microscopic approach of the normal stress and static shear modulus of electrorheological suspensions.

The high strain compression of closed-cell polymer foams

A compressed closed-cell polymer foam was modelled using a BBC lattice model of tetrakaidecahedral cells, loaded in the [001] direction. The contributions of cell face tensions and edge bending were analysed, assuming that the faces act as membranes, for a linearly-elastic, or a yielding material. The moduli and tensile yield stresses of highly oriented polymer films were measured to provide data for modelling, and the amount of polymer in the foam cell faces found to be high. Tensile face strains are predicted to reach 40% of the foam compressive strain. The predicted Youngs moduli are slightly low, because compressive face stresses are ignored, but Poissons ratio is correctly predicted. The compressive foam yield stress is predicted to depend on tensile yielding of the cell faces. Predicted values are close to experimental values for polyethylene foams, but half those of polystyrene extruded foams. The latter foam may collapse in compression when face yielding commences, rather than by the collapse mechanism of the model.

Molecular Orientation and Dielectric Anisotropy in Polyimide Films As Determined by the Microwave Method

Molecular orientation and dielectric anisotropy of polyimide films was studied by the microwave method. The average direction and degree of orientation of the main chains were in good agreement with those determined by the conventional methods utilizing the mechanical breaking and the polarized infrared absorbance. The results gave a definite evidence for the usefulness of the microwave method to study the correlation between the mechanical and high-frequency dielectric properties and molecular orientation of polymer films.

延伸プラスチックフィルム用赤外線ゲージ

This paper describes the methods and apparatus for measuring accurately the thickness of thin oriented polymer films. Three key aspects of the new method are as follows:(1) The technique eliminating optical interference effects occurred with thin films by using plane polarized light incident at Brewster's angle;(2) The implementation of multivariate regression models based on the inverse representation of Beer's law or P-matrix approach with optimal wavelengths, canceling dichroic effects with anisotropic materials such as oriented polymer films;(3) The design of optics to be quite tolerant to movement of the film in both height and angle