Multilayer Polymer Films Research Articles

Optical Properties of Multi-Layer Structures of Nanometric Polymer Photonic Crystals

Photonic crystals are attracting a lot of attention due to their ability to manipulate and guide the light. Sandwiching 3-dimensional styrene-based photonic crystals between polymeric multi-layer films such as polystyrene and polymethyl methacrylate is reported in this article. Polystyrene and polymethyl methacrylate solutions and a suspension of polymeric nano particles were cast using a specially designed spin-casting machine to produce a periodic multi-layer structure. In the next step, the optical properties of multi-layer structures were investigated via spectrophotometric techniques. A film of styrene-based nano particles has a blue-green reflection, which being affected by the suspension particles sandwiched between polystyrene and polymethyl methacrylate layers, shifts to red whereas the multi-layer structure demonstrates a green color. Moreover, the effects of the observer's viewing angle on the color shift were studied by means of goniospectrophotometric technique.

Confined crystallization in polymer nanolayered films: A review

Abstract

Multilayer reactive barrier materials

A model is developed and solved analytically and numerically to describe the barrier properties of multilayer films with alternating reactive and inert layers. Incorporation of reactive scavenging sites in packaging materials can significantly improve their barrier properties. Due to mechanical and optical requirements, barrier films typically consist of polymer blends or multilayer films of the scavenging material and an inert supporting polymer. Because composite reactive barriers are expected to operate for months or years, purely experimental characterization is not practical and models are needed to optimize the configurations and to confidently extrapolate experimental data. The model for multilayer films is solved numerically over a wide parameter space, varying physical properties and layer configuration to determine the flux and time lag. Asymptotic analysis of the model is used to develop analytical predictions for transport behavior at early and long times. The performance of multilayer composites is compared to polymer blends and discussion of the most suitable configuration for different scenarios is presented.

Study of the cooperativity at the glass transition temperature in PC/PMMA multilayered films: Influence of thickness reduction from macro- to nanoscale

In multilayered polymer films, the influence of thickness reduction on the glass transition temperature (Tg) and cooperatively rearranging region (CRR) size was investigated using temperature modulated differential scanning calorimetry (TMDSC). The materials used in this work are multilayered films comprising tens to thousands of alternating layers of two polymers, Bisphenol A Polycarbonate (PC) and polymethyl-methacrylate (PMMA) fabricated by layer multiplying coextrusion technique. The TMDSC measurements enable the calculation of the average values of CRR parameters at the dynamic glass transition temperature (Tg) using Donth’s method. The molecular mobility in each polymer is found to be altered in entirely different ways as the thickness of each component became thinner than 125 nm, whereby the polymers exist as two dimensional layers under those conditions. PC exhibits a drastic decrease in cooperativity volume at the glass transition while slight modifications are observed for PMMA. These observations are discussed in regard with the role of the large interface amount between the two different polymers and the evolution of the macromolecule conformations.

Metal ions/ion clusters transport in glassy polymer films: construction of multi-layered polymer and metal composite films

The addition of a metal complex and an additive to a polymer supported on a reflective surface, which was then exposed to monochromatic ultraviolet (UV) light, resulted in well-ordered metal nanoparticles. Their row spacing is similar to the distance between the constructive interference regions. This could occur even in glassy polymers. Transmission electron microscopy, absorption spectroscopy and dynamic secondary ion mass spectrometry in conjunction with molecular dynamics simulation all revealed how and why the metal ions and/or ion clusters were transported in the glassy polymer films. Furthermore, the diffusion coefficient of the metal ions and/or ion clusters in the film, probably in the shape of ion clusters, was discussed. Our results showed novel criteria to design and construct multi-layered polymer and metal composite films using a simple, inexpensive method.

Liquid Crystalline Materials for Biological Applications.

Liquid crystals have a long history of use as materials that respond to external stimuli (e.g., electrical and optical fields). More recently, a series of investigations have reported the design of liquid crystalline materials that undergo ordering transitions in response to a range of biological interactions, including interactions involving proteins, nucleic acids, viruses, bacteria and mammalian cells. A central challenge underlying the design of liquid crystalline materials for such applications is the tailoring of the interface of the materials so as to couple targeted biological interactions to ordering transitions. This review describes recent progress toward design of interfaces of liquid crystalline materials that are suitable for biological applications. Approaches addressed in this review include the use of lipid assemblies, polymeric membranes containing oligopeptides, cationic surfactant-DNA complexes, peptide-amphiphiles, interfacial protein assemblies and multi-layer polymeric films.

Thickness effects on the optical properties of layer-by-layer poly(p-phenylene vinylene) thin films and their use in energy-modulated structures

Poly(p-phenylene vinylene) (PPV) thin films were produced by layer-by-layer (LbL) method, using soluble PPV-precursor and dodecylbenzenesulfonate salt (DBS). The amount of deposited layers strongly influences the optical properties of the thermally converted PPV film. The absorbance and luminescence spectra of ultra-thin films (consisting of only two or three PPV layers) are shifted to smaller wavelengths with respect to spectra of thicker films. This is related to the smaller average conjugation length of polymer chains, resulting in a higher HOMO–LUMO gap energy of the material. However, if a thick film is produced by repeating the deposition process and thermal conversion of ultra-thin layers, the optical spectra are still displaced to higher energies in comparison with those of thicker films produced by the conventional continuous deposition of layers. This result enabled the production of multilayered polymeric films with modulated energy profile, taking the number of deposited layers as the only variable in the manufacturing process of the structure. The aim is to guide the excitation to specific regions of the material through the Förster-type energy transfer processes. Such systems can be used at interfaces electrode/polymer and/or electrode/polymeric active layers in order to improve the performance of organic optoelectronic devices.

ITO/Ag/ITO Multilayer Polymer Films by Roll-to-Roll Process and Performance of Flexible OLED Devices

In this study polyethylene naphthalate(PEN) and polyethersulfone(PES) films were chosen as a flexible substrates for fabrication of organic light emitting diode(OLED) devices. Hard coating was applied on both PEN and PES films utilizing UV curable resin. The transparent conductive ITO/Ag/ITO multilayer was deposited by the roll-to-roll sputter on the polymer films with hard coating. The UV hard coating of thin film on the polymer films improved both the surface roughness (50% in case of PEN film) and the transmittance in the visible region. In the subsequent multilayer transparent conductive layer formation, the optimum condition was obtained in the ITO(50 nm)/Ag(17 nm)/ITO(50 nm) multilayer structure. The OLED's fabricated with the optimized multilayer conductive films exhibited high luminance and current efficiency under low operation voltages.

A comparison of different approaches for depth profiling of films and coatings by confocal Raman microscopy

We compare and analyze different approaches to perform depth profiling of polymer films and coatings by confocal Raman microscopy (CRM). Data were generated using three methodologies: conventional metallurgical objectives, oil-immersion optics and numerical post processing of the as-measured intensity profiles, via an optimized deconvolution technique adapted to CRM. A series of bi- and multi-layered polymeric films were used as test systems. Strengths and weaknesses of each methodology are evaluated in terms of delivered depth resolution, signal throughput and flexibility. It is shown that the application of regularized deconvolution on data obtained from dry objectives yielded intensity profiles with a quality comparable, in some cases superior, to those obtained with immersion objectives, with the advantage of being totally non-invasive.

Analysis of scratch-induced damages in multi-layer packaging film systems

Scratch-induced damages on multi-layer polymeric packaging films are investigated using laser confocal microscopy. Films were tested using a modified version of the standardized linearly increasing load scratch test (ASTM D7027-05/ISO 19252:2008), which has been successfully demonstrated to correlate field data of commercial films with lab data. Scratch test results show clear distinction between the two model film systems on both the interior and exterior surfaces. Microscopy was performed to investigate the feasibility of utilizing this methodology as a tool for packaging film structure evaluation by determining the effect each layer has on the resistance of scratch damages. It is shown that the film exhibiting superior scratch performance also possesses significantly better stress distribution through its layers during the scratch test, as well as better layer adhesion during severe deformation. The scratch test is capable of discerning film mechanical integrity in a layer-by-layer fashion.

Release of vancomycin from multilayer coated absorbent gelatin sponges

Wounds have the potential to become infected during any surgical procedure. Gelatin sponges that are commonly used to absorb blood during invasive surgeries would benefit tremendously if they released antibiotics. In this work, we have examined coating a commercial gelatin sponge with degradable polymer multilayer films containing vancomycin. The effect of the film on sponge absorption capabilities and the effect of the sponge on drug release kinetics were both examined. Application of vancomycin containing layer-by-layer assembled films to this highly porous substrate greatly increased drug loading up to approximately 880% compared to a flat substrate. Vancomycin drug release was extended out to 6 days compared to 2 days for film coated flat substrates. Additionally, the absorbent properties of the gelatin sponge were actually enhanced by up to 170% due to the presence of the vancomycin film coating. A comparison of film coated sponges with sponges soaked directly in vancomycin demonstrated the ability of the multilayer films to control drug release. Film released vancomycin was also found to remain highly therapeutic with unchanged antimicrobial properties compared to the neat drug, demonstrated by quantifying vancomycin activity against Staphylococcus aureus in vitro.

Imaging the effect of dielectric breakdown in a multilayered polymer film

AbstractThe dielectric strength and energy storage capability of poly(vinylidene fluoride‐hexafluoropropylene) copolymer (P[VDF‐HFP]) films are enhanced by interleaving layers of PVDF copolymer with thin layers of polycarbonate (PC). To gain insight into the breakdown processes in such materials, focused ion beam (FIB) milling in conjunction with scanning electron microscopy (SEM) was used to study the effect of a breakdown on the film. FIB can sequentially mill cross sections that are each imaged by SEM. The technique can provide quasi‐3D images across the film and give a detailed view of the damage caused by an electrical breakdown. Here, breakdowns initiated using a needle‐plane electrode configuration were imaged. In homogeneous films, the damage was confined to the small volume at the pinhole site. In 32‐layer 50/50 PC/P[VDF‐HFP] multilayer films, damage extending laterally up to ∼ 15 μm into the film along the layer interfaces was seen. In addition to the delamination, layer buckling and distortion were apparent. The damage varied with the sample orientation, but the images indicate that the interfaces play an important role in the breakdown. They suggest that modifying the interface properties can be a strategy to further improve the dielectric strength of multilayer polymer dielectric materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Photocrosslinkable diazoresin/pectin films – Synthesis and application as cell culture supports

Multilayer polymeric films composed of diphenylamine-4-diazoresin (DR), a synthetic polycation, and pectin (Pec), a polyanionic natural polysaccharide, were obtained using a layer-by-layer method (LbL). The films was photocrosslinked by the irradiation with 350 nm light which resulted in their stabilization against different solvents. The nanostructure of the films was studied using AFM microscopy. Irradiation of the films resulted also in the change of the zeta potential of both DR and Pec outermost layer to more negative values and in the increase of the film hydrophobicity as found from the contact angle measurements. The DR/Pec films have been shown to support cell growth and osteogenic potential of cell culture supports in tissue engineering, as found from the experiments with human bone marrow stromal cells (hMSCs).

Functionalization of polymer multilayer thin films for novel biomedical applications

The design of functional polymer multilayer thin films with nanometer scale control is of great interest for biomedical applications such as tissue engineering, targeted drug delivery, controlled release system, and regenera- tive medicine. Various functions and properties of polymer thin films can be easily programmed and realized by the layer-by-layer assembly strategy, which is a facile and versatile deposition method to prepare well-defined biomedical multilayer platforms due to its benign process to prepare films under mild conditions and the capability of incorporating bioactive materials at a desired location within the films. Particularly, the fine tuning of physicochemical and biologic- al properties of multilayer thin films is significantly important for designing novel biomedical platforms capable of adjusting the cellular functions. In this review, we focus on the overall background of the layer-by-layer assembly as well as the tuning of multilayer film properties and the programming of biological functions into the polymer thin films with a view on the control of cellular functions. Furthermore, we highlighted the recent achievements toward the design of novel biomedical platforms based on functionalized polymer multilayer thin films.

Life Cycle Assessment of multilayer polymer film used on food packaging field

The environmental impact of a multilayer polymer film, Low Density Poly Ethylene/Polyamide system (LDPE/PA), generally used on food packaging field, was estimated using life cycle assessment (LCA). The aim of the work was to understand how to reduce the environmental pressure from plastic packages for its lower recovery and reuse, which can be improved by developing material recovery or other appropriate recycling technology to improve the cyclic materials flows and recycling ratio. LCA is a tool specifically developed for assessing the overall environmental burden of a product, including the system used for manufacturing it and its end-of-life treatment. This work provides a cradle-to-grave LCA study of a food packaging envelope made with a multilayer polymer film, with two different depth of 70 and 90 micron, and a study of the possibility to utilize a 50% of recycled LDPE and PA polymer pellets in order to reduce the environmental impact. A one square meter envelope is used as functional unit.

Electromechanical Response of Multilayered Polymer Films for High Energy Density Capacitors

ABSTRACTMultilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (EB> 750 kV/mm) and an increased energy storage density (Ud ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.

Tunable Vancomycin Releasing Surfaces for Biomedical Applications

Local drug delivery methods allow for the opportunity to supply potent multispectrum antibiotics such as vancomycin hydrochloride to sites of infection, while avoiding systemic toxicity. In this work, layer-by-layer assembly of polymer multilayer films is applied to create vancomycin delivery coatings. By taking advantage of the versatile layer-by-layer spray and dip coating techniques, thin films were generated based on electrostatic and other secondary interactions discovered to exist between the film components. The importance of film interdiffusion during growth in promoting interactions between film components is found to be critical in the direct incorporation of the weakly charged vancomycin drug in these multilayer films. The resulting coatings are engineered with unprecedented drug densities ranging from 17-220 μg mm(-3) (approximately 20 wt%) for films that are micron to submicron scale in thickness, delivering vancomycin over timescales of 4 h to 2.5 days. The released drug is highly effective in inhibiting Staphylococcus aureus growth in vitro. Taking advantage of the difference in release characteristics between dip and spray assembled films, a composite film architecture was engineered to have both a bolus vancomycin release followed by a period of linear sustained drug release. The control over drug densities and release profiles displayed in this work is necessary to address the requirements of varying medical conditions, including those where immediate infection elimination is needed or long term infection prevention is required.

Correlation functions and optical effects in surface layers of polymer films

The calculated dependences of the quadrupole orientation order parameter on the Kuhn segment length adequately describe the experimental data obtained by the birefringence method for multilayer polymer films. The transverse orientation correlations of chain segments decrease according to a power law, like in 2d infinite systems. The fluctuations of the 3d long-range orientation order in the layer plane increase with the increasing anisotropy of interactions in the system.

Controlled Fabrication of Fluorescent Barcode Nanorods

We report a novel technique for generating polymer fluorescent barcode nanorods by reactive ion etching of polymer multilayer films using nonclose-packed (ncp) colloidal microsphere arrays as masks. The fluorescent polymer multilayer films were spin-coated on a substrate, and ncp microsphere arrays were transferred onto these films. The exposed polymers were then etched away selectively, leaving color-encoded nanorods with well-preserved fluorescent properties. By modifying the spin-coating procedure, the amount of polymer in each layer could be tuned freely, which determined the relative fluorescence intensity of the barcode nanorods. These nanorod arrays can be detached from the substrate to form dispersions of coding materials. Moreover, the shape of the nanorods is controllable according to the different etching speeds of various materials, which also endows the nanorods with shape-encoded characters. This method offers opportunities for the fabrication of novel fluorescent barcodes which can be used for detecting and tracking applications.

Correlation Functions and Optical Effects in Surface Layers of Polymer Films

The calculated dependences of the quadrupole orientation order parameter on the Kuhn statistical segment length properly describe the experimental data, obtained by the film birefringence method for different multilayer polymer films. Transverse orientation correlations of chains segments decrease according to a power law, as in the case of infinite two-dimensional systems. The fluctuations of three-dimensional long-range orientation order in the plane of the layers are observed. These fluctuations are enhanced when the anisotropy of intra- and interchain interactions increase in the film.