Stretched Polymer Films Research Articles

New Approaches to Stretched Film Sample Alignment and Data Collection for Vibrational Linear Dichroism.

Rapid measurements of vibrational linear dichroism (VLD) infrared spectra are shown to be possible by using stretched polymer films and an extension of existing instrumentation designed for vibrational circular dichroism spectroscopy. Earlier techniques can be extended using additional inexpensive polymer substrates to record good-quality VLD spectra of a significantly wider range of compounds with comparatively short sample-preparation times. The polymer substrates used, polyethylene and polytetrafluoroethylene, are commonly available and inexpensive, and samples are more easily prepared than that for many earlier stretched-film and crystal studies. Data are presented for neutral hydrophobic organic molecules on hydrophobic films including acridine, anthracene, fluorene, and recently synthesized S-(4-((4-cyanophenyl)ethynyl)phenyl)ethanethioate. We extend the approach to polar or ionic species, including 2,2'-bipyridine, 1,10-phenanthroline, and sodium dodecyl sulfate, by oxidizing polyethylene films to change their wetting properties. The combination of new instrumentation and modified sample preparation methods is useful in basic spectroscopy for untangling and assigning complicated infrared spectra. Nevertheless, it is not a panacea as surface-adsorbed molecules are often not monodispersed, and higher analyte concentrations can lead to aggregation and resonance phenomena that have previously been observed for infrared spectra on surfaces. These effects can be assessed by varying the sample concentration. The focus of this paper is experimental, and detailed analysis of most of the spectra lies outside its scope, including some well-studied compounds such as acridine and anthracene that allow comparisons with earlier research.

Enhancing the thermal conductivity in electrocaloric polymers by structural orientation for collaborative thermal management

Endowing bulk electrocaloric polymers with excellent thermal conductivity is a superior solution to the high-efficient and precise management of tremendous heat from high-power-density electronic devices. Semi-crystalline polymer P(VDF-TrFE-CFE), i.e., poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), has a predominant amorphous phase of randomly entangled chains and abundant interface, leading to localized behavior in phonon heat conduction and thereby low thermal conductivity. To enhance the thermal transport performance, electrocaloric polymer films were mechanically stretched or fabricated by electrospun to achieve highly aligned molecular chains. Chain orientation brought about a 2.4- and 1.6-times increase in the thermal diffusion coefficient of the stretched and electrospun films, respectively. Interestingly, after mechanical stretching, the thermal conductivity of the film was increased by a factor of two. In contrast, the electrospun film had a slightly lower thermal conductivity than that of the unoriented one. A remarkable discrepancy in the electrocaloric properties was observed, where the stretched polymer film reached a much higher adiabatic temperature change under an applied electric field than that of the electrospun film. Our strategy provides a perspective on designing a promising thermal management system through the integration of active refrigeration and passive heat dissipation in bulk electrocaloric polymers.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Small-Angle Scattering and Radiation Polarization by a Stretched Polymer Film with Nematic Liquid Crystal Droplets Having a Single-Domain Structure

The coefficient of directed transmittance of a stretched polymer-dispersed liquid crystal film with a defect-free single-domain liquid crystal droplet structure formed by a stretched surfactant-doped film and the polarization degree of forward-transmitted light in the visible and near-infrared spectrum ranges are studied. Results are presented for the 5CB, E7, and E44 nematic liquid crystals. Dependences of the transmission coefficient and polarizing ability of the film on the photodetector field of view are studied. Relationships allowing one to determine film parameters at which the transmission coefficient and polarizing ability of the films simultaneously reach values close to limit ones (0.5 and ±1.0, respectively) are obtained in the Foldy–Twersky and anomalous diffraction approximations.

Modeling of internal residual stress in linear and branched polyethylene films during cast film extrusion: Towards a prediction of heat-shrinkability

The singular property of shrinkage is used in the packaging sector to wrap products. Polyethylene film products are mostly produced by either blown or cast film extrusion. During processing, under the effect of drawing, the molten polymer is stretched in one or two dimensions according to the cast or blown film extrusion. When the resulting solid film is subjected to a sudden increase in temperature, it shrinks as a result of the relaxation of polymer chains that were oriented under stress and frozen in a stretched state upon processing resulting in internal residual stresses. A general viscoelastic model in the framework of large strain has been used to predict the development of the internal residual stresses stored during the stretching stage of the process. Linear and branched polyethylenes (LLDPE, LDPE) were used as model matrices and additional blends (80/20%, 50/50% and 20/80% LDPE/LLDPE w/w) of pure resins were also studied. Moreover, as properties of stretched films are highly dependent on processing conditions, the influence of the draw ratio was also investigated. Contrasted mechanical response in strain of the LDPE and LLDPE films under stretching were observed and justified by differences in their rheological behavior due to long branch chains (LCB) in LDPE. The modeled ultimate stress stored in LDPE and LLDPE films was compared to the shrinkage stress measured by Dynamic Mechanical and Thermal Analysis (DMTA). Both stresses were found to be in the same order of magnitude which constitutes an interesting result for the prediction of heat-skrinkability of stretched polymer films.

Computation of refractive index and optical retardation in stretched polymer films.

Functional polymer films are key components in the display industry, and the theoretical prediction of the optical properties of stretched polymer films is important. In this study, we try to establish the theoretical calculation process without an empirical database to predict the refractive index, including wavelength dispersions and optical retardation of stretched polymer films using several commercial simulation tools. The polarizability tensor and molecular volume for periodic units of polymers are accurately simulated, resulting in the accurate prediction of the mean refractive index and its dispersion for raw polymer materials. The birefringence of stretched films is also calculated to predict reasonably accurate optical properties of stretched films. The simulation method is an effective way that requires a relatively short time and low cost to develop new types of polymer films.

Mechanical tuning of plasmon resonances in elastic, two-dimensional gold-nanorod arrays

Two-dimensional gold-nanorod arrays (2D-GNA) exhibit distinct resonance peaks in the visible wavelength range that are clearly associated with long and short axis plasmon oscillations. In this paper, we demonstrate a flexible and reproducible way for controlling the plasmon resonance of such 2D-GNAs in-situ, even post-fabrication process, simply by embedding free-standing nanorod arrays into an elastomer thin film. Stretching the polymer film shows the plasmon long-axis resonance to red-shift proportionally to the applied force by as much as 20~nm by increasing the center-to-center distance between individual nanorods. Releasing the load elastically relaxes the stretched polymer film, hence allowing the recording of cyclic load curves while varying the spectral response in-situ. Notably, film stretching along the substrate plane (x-axis) results in a uniaxial distortion of the nanorod lattice. We show how to account for this anisotropic strain in both the experiment and our complementary finite element modelling simulations, which then both match very well. This novel work illustrates both the feasibility and reliability when integrating 2D-GNAs for potential flexible, plasmonic applications.

An investigation of cutting resistance in stretched polymer films

An investigation is made into the fracture properties of polymer films and laminates under cutting by a sharp tool and lateral tension under pure shear conditions. The method involves use of a sharp razor blade applied to the crack tip of polymer films which are also stretched orthogonal to the direction of the blade. The reaction force is measured as the cutting tool cuts the material and the force from applying a lateral strain is measured. The analysis and tests assume quasi-static conditions. The method is applied to a polyester film and three polyester laminates.Steady-state cutting forces are observed from cutting tests and loads at crack initiation are observed from lateral stretching tests. With fracture mechanics analysis the energy contributions from cutting and tearing are used to determine apparent fracture properties from the experimental results. It is observed that the cutting and tearing tests yield similar fracture toughness properties for the three tested polyester laminates, despite the different crack tip geometry at the point of crack growth. However, significantly larger fracture toughness values are measured from tearing tests versus cutting tests for the tested polyester film.

Anisotropic optical properties of oriented silver nanorice and nanocarrots in stretched polymer films

Stretching-induced orientation of both silver nanorice and silver nanocarrots dispersed in or deposited on the surface of poly(vinyl alcohol) (PVA) films was investigated using polarized UV-visible-near-infrared (NIR) spectroscopy and atomic force microscopy (AFM). The results show that the film stretching not only aligns the long axis of individual nanorice or nanocarrots preferentially along the stretching direction, but also induces assembly of these nanostructures into oriented arrays of random lengths in the deformation process. Consequently, the longitudinal surface plasmon resonance peaked at 820 nm for nanorice and 1050 nm for nanocarrots before stretching can be replaced by continuous extinction over the entire 800-1800 nm NIR spectral range after stretching. Stretched PVA films containing either silver nanorice or nanocarrots thus display polarization-dependent transmission of NIR light.

Shrinking and Light Diffraction of the Self-Organized Polystyrene-block-Polybutadiene Microporous Film Deposited on a Stretched Polymer Film by Thermal Contraction

Polystyrene-block-polybutadiene( PS-b-PB) microporous polymer honeycomb films with hexagonal pores were prepared by solvent evaporating self-organization under humid conditions( polystyrene-blockpolybutadiene,referred to as: PS-b-PB,the same below). The PS-b-PB honeycomb films were shrunk twice by using polythene shrinkable films to form ordered porous film with small pores. The pores in film changed from circular to rectangular or fusiform after shrinkage; the pore size of film was shrunk from micron into submicron. Scanning electron microscopy( SEM) was used to study the generation mechanism of two films. The results showed that PS-b-PB could transform the invisible thermal field signals into visible optical signals based on the advantages combination of polystyrene and polybutadiene which flat films structure remained after contraction.

Non-destructive quantification of alignment of nanorods embedded in uniaxially stretched polymer films

Among several methods developed for uniaxial alignment of metallic nanorods for optical applications, alignment by film stretching consists in embedding the rods in a transparent thin film of thermoplastic polymer, followed by simultaneous heating and uniaxial stretching of the composite film. As to the quantification of the resulting alignment, it has been limited to statistical calculations based on microscopic examination, which is incomplete, subject to errors due to geometric distortions of the scanning electron microscope images and destructive, since it involves cutting of samples. In contrast, we present in this paper a non-destructive quantification of the average orientation of the rods, based on a probabilistic approach combined with numerical simulations of absorbance spectra and spectrometric characterization of the composite film. Assuming electromagnetically non-interacting rods, we consider the longitudinal absorbance peak of their ensemble to consist of the superposition of their individual spectra that we obtain by numerical simulation using the size and shape adapted dielectric function of the metal and the finite difference time domain method. The accuracy of the solution depends on the number of discretization intervals, the accuracy of the numerical simulations, and the accurate knowledge of the polydispersity of the rods. For the sake of concreteness, we used nanorods to describe the quantification steps but the method is equally valid for any dichroic particles.

Dichroic Optical Properties of Uniaxially Oriented Gold Nanorods in Polymer Films

Applications based on the optical excitation of the longitudinal surface plasmon resonance of gold nanorods (AuNRs) work at highest efficiency if all component AuNRs can be maximally excited simultaneously. This can be achieved in aligned AuNR structures, such as those embedded in uniaxially stretched polymer films. Since too high heating temperatures during film stretching cause reshaping and alteration of optical properties of the rods, a maximum allowable heating temperature is determined. The alignment of the rods is quantified by an orientational order parameter of 0.92 based on a statistically significant sample of assumed t distributed means and obtained by scanning electron microscopy. We show that a stretched AuNRs-PVA composite film has optical properties that approach the dichroic properties of an idealized ensemble of fully aligned, identical, and non-interacting AuNRs embedded in a PVA film. The idealized system is provided by FDTD simulations of a single AuNR, which we carried out using the size- and shape-adapted dielectric function of gold and the software RSOFT.

Anisotropy of light absorbed by an ensemble of CdSe quantum nanoplates

The anisotropy of the optical properties of CdSe quantum nanoplates is investigated, using the methods of absorption spectroscopy. It is experimentally established that the optical properties of the quantum nanoplates are anisotropic. Spectral dependences are obtained for the absorption anisotropy of ensembles of nanocrystals ordered in a stretched polymer film. A technique has been developed for creating elastic polymer films made from polyvinyl butyral with a high concentration of quantum nanoplates.

Infrared and fluorescence spectroscopy investigation of the orientation of two fluorophores in stretched polymer films

The simultaneous orientation of poly(1,4-butylene)succinate (PBS) and 4,4′-bis(2-benzoxazolyl)stilbene (BBS) or 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT) in PBS–BBS and PBS–BBT films was investigated during stretching at 80 °C, about 33 °C below the PBS melting temperature. The PBS orientation was first investigated using the 3430 cm−1 infrared band and its order parameter <P2> goes from 0.36 at a local strain of 359% for pure PBS to 0.66 in blends containing 6 wt % of BBT at a local draw ratio of ≈350% (or 0.56 with 5 wt % of BBS). At the same time, BBT shows in the same films an orientation parameter <P2> reaching a maximum of 0.31 at a local strain of ≈350%, using the 1580 cm−1 band. Since polarized FT-IR was unable to provide the orientation of BBS due to overlapping bands with PBS, polarized fluorescence spectroscopy was then used and reveals an apparent order parameter of 0.32 for BBS monomers (or 0.34 for BBT monomers), but to no orientation of BBT aggregates and BBS excimers. In other words, the two small molecules behave similarly in terms of orientation independently of their molecular shape and packing. BBS and PBS both exhibit a sharp increase of S and <P2> when reaching a BBS concentration of ≈0.08 wt %, whereas BBT and PBS show a smooth increase of S and <P2>, respectively, in films containing BBT. The sharp increase, or transition in orientation, is accompanied by a conversion of BBS from monomers to excimers, whereas BBT-containing films show a regular increase of the number/size of BBT aggregates. These results indicate that the dye (BBS or BBT) has a profound influence on the orientation of the semi-crystalline polymer (PBS) since its <P2> almost doubles at dye concentrations above 0.08 wt %. The results also suggest that the use of a fluorescent probe to follow the polymer chain orientation is not applicable for such systems.

Electrically controlled polarized photoluminescence of CdSe/ZnS nanorods embedded in a liquid crystal template

A novel homogeneous composite material, consisting of luminescent CdSe/ZnS quantum nanorods, embedded in the nematic liquid crystal 5CB, has been prepared. Liquid crystal cells and free-standing stretched polymer films incorporating this composite material were characterized using polarized micro-photoluminescence and electro-optical measurements under an applied electric field. A liquid crystal induced, macroscopic orientation of the nanorods in a thin layer of the material has been demonstrated. A conventional liquid crystal cell, filled with this composite, exhibits 40% modulation of the nanorod’s photoluminescence intensity when subjected to an external electric field. These results indicate that quantum nanorods may have practical applications in photonic devices.

Hybrid Monte-Carlo simulations of fluorescence anisotropy decay in three-component donor–mediator–acceptor systems in the presence of energy transfer

Hybrid Monte-Carlo simulation algorithm of fluorescence anisotropy decay for donor–mediator–acceptor systems has been proposed. The results of hybrid Monte-Carlo simulations are compared with the results of Monte-Carlo step by step simulations. Very good agreement between both Monte-Carlo simulations has been obtained. The hybrid Monte-Carlo simulation of emission anisotropy is characterized by very good accuracy and little time consumption. As an example the donor–mediator–acceptor system in uniaxially stretched polymer film has been studied.

Miniaturization of Surface Patterns by Combination of Contact Etching Lithography and Multi-step Shrinking of Stretched Polymer Films

Miniaturization of Surface Patterns by Combination of Contact Etching Lithography and Multi-step Shrinking of Stretched Polymer Films

Erratum: Miniaturization of Surface Patterns by Combination of Contact Etching Lithography and Multi-step Shrinking of Stretched Polymer Films

Erratum: Miniaturization of Surface Patterns by Combination of Contact Etching Lithography and Multi-step Shrinking of Stretched Polymer Films

Unusual fluorescence anisotropy spectra of three-component donor–mediator–acceptor systems in uniaxially stretched polymer films in the presence of energy transfer

Energy transfer was studied for donor–mediator–acceptor systems in uniaxially stretched polymer films. The systems differ in the ability of mediator transition moment to orientate in the matrix. It was found that acceptor fluorescence remains polarized in the stretched matrix irrespectively of mediator. This means that information on the orientation of electric vector of the exciting light was conserved after energy transfer. In disordered system sensibilized fluorescence of mediator and acceptor is strongly depolarized. The effect of transition moments correlation on 〈 κ 2〉 in the stretched matrix is presented using Monte-Carlo simulation.

Polarized ff-Emission of Terbium(III) by using the Stretched Polymer Film Technique

A Novel coordination system with ff-emission of Tb(III) was obtained on a polyvinyl alcohol (PVA) film surface. On this film the ff-emission is polarized, and is intensified by polymer stretching. XAFS spectra show that the mean bond distances between Tb(III) and the nearest neighbour atoms of the 1,10,-phenanthroline ligand on the film are close to those in [Tb(SA)3], Tb(NO3)H2O and [Tb(phen)2(NO3)3].