The ability to control the propagation direction of light has long been a scientific goal. However, the fabrication of large-scale optical angular-range selective films is still a challenge. This paper presents a polymer-enabled large-scale fabrication method for broadband angular-range selective films that perform over the entire visible spectrum. Our approach involves stacking together multiple one-dimensional photonic crystals with various engineered periodicities to enlarge the bandgap across a wide spectral range based on theoretical predictions. Experimental results demonstrate that our method can achieve broadband transparency at a range of incident angles centered around normal incidence and reflectivity at larger viewing angles, doing so at large scale and low cost.

The Cherenkov effect enables a valuable tool, known as the Cherenkov detector, to identify high-energy particles via the measurement of the Cherenkov cone. However, the sensitivity and momentum coverage of such detectors are intrinsically limited by the refractive index of the host material. Especially, identifying particles with energy above multiple gigaelectronvolts requires host materials with a near-unity refractive index, which are often limited to large and bulky gas chambers. Overcoming this fundamental material limit is important for future particle detectors yet remains a long-standing scientific challenge. Here, we propose a different paradigm for Cherenkov detectors that utilizes the broadband angular filter made from stacks of variable one-dimensional photonic crystals. Owing to the Brewster effect, the angular filter is transparent only to Cherenkov photons from a precise incident angle, and particle identification is achieved by mapping each Cherenkov angle to the peak-intensity position of transmitted photons in the detection plane. This unique property of the angular filter is exceptionally beneficial to Cherenkov detection as it enables the realization of a non-dispersive pseudo refractive index over the entire visible spectrum. Moreover, such a pseudo refractive index can be flexibly tuned to arbitrary values, including those close to unity. Our angular-selective Brewster paradigm offers a feasible solution to implement compact and highly sensitive Cherenkov detectors especially in beam lines and it can cover a wide momentum range using readily available dielectric materials.

ABSTRACTAdvanced film capacitors require polymers with high thermal stability, high breakdown strength, and low loss for high temperature dielectric applications. To fulfill such requirements, two polymer multilayer film systems were coextruded via the forced assembly technique. High glass transition temperature (T g) polycarbonate (HTPC, Tg = 165 °C) and polysulfone (PSF, Tg = 185 °C) were multilayered with a high dielectric constant polymer, poly(vinylidene fluoride) (PVDF), respectively. The PSF/PVDF system was more thermally stable than the HTPC/PVDF system because of the higher Tg for PSF. At temperatures lower than 170 °C, the HTPC/PVDF system exhibited comparable breakdown strength and hysteresis loss as the PSF/PVDF system. While at temperatures above 170 °C, the PSF/PVDF system exhibited a higher breakdown strength because of the higher Tg of PSF. The electric displacement‐electric field (D‐E) loop behavior of the PSF/PVDF system was studied as a function of temperature. Moreover, a melt‐recrystallization process could further decrease the hysteresis loss for the PSF/PVDF system due to better edge‐on crystal orientation. These results demonstrate that PSF/PVDF and HTPC/PVDF systems are applicable for high temperature film capacitors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47535.

Compared with chemical modification of ferroelectric poly (vinylidene fluoride) (PVDF) for electric energy storage, polymer blends, whether miscible or immiscible, represent a much easier approach to suppress the ferroelectricity of PVDF. In this study, we explored both miscible [i.e., poly (methyl methacrylate) or PMMA] and immiscible (i.e., polycarbonate or PC) blends with poly (VDF-co-hexafluoroethylene) [P(VDF-HFP)], as well as the PC/P(VDF-HFP) multilayer films. For miscible PMMA/P(VDF-HFP) blend films, the addition of PMMA significantly decreased the crystallinity of P(VDF-HFP). At a high PMMA content of ca. 40 wt%, the stretched PMMA/P(VDF-HFP) blend films started to exhibit the linear dielectric behavior with suppressed ferroelectricity. For the immiscible PC/P(VDF-HFP) blend films, a high PC content of 50 vol% was required to suppress the ferroelectricity in P(VDF-HFP). Instead, the PC/P(VDF-HFP) multilayer films started to show linear hysteresis loops when the content of P(VDF-HFP) was only 30 vol%. More importantly, the PC/P(VDF-HFP) multilayer films exhibited significantly higher breakdown strength than the blend films. This could be attributed to the perpendicular interfaces (with respect to the applied electric field), which serve as effective blocks for hot electrons injected from the metal electrodes to pass through the film. From this study, compared to conventional miscible and immiscible blends, multilayer films are promising for next generation film capacitors, aiming to achieve high temperature tolerance, high energy density, and low loss simultaneously.

Generalizing broadband angular selectivity to both polarizations has been a scientific challenge for a long time. Previous demonstrations of the broadband angular selectivity work only for one polarization. In this paper, we propose a method that can achieve polarization-independent optical broadband angular selectivity. Our design is based on a material system consisting of alternating one dimensionally anisotropic photonic crystal (1D PhC) stacks and half wave plates. 1D PhC stacks have an angular photonic band gap for p polarized light and half-wave plates can convert s-polarized light to p-polarized light. By introducing alternating 1D PhC stacks and half-wave plates, we predict that one can achieve a central transmission angle at normal incidence and an angularly selective range of less than 30 across the whole visible spectrum.

Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

Current development of advanced power electronics for electric vehicles demands high temperature, high energy density, and low loss polymer dielectrics. Multilayer films (MLFs), which are comprised of alternating high temperature/low loss linear dielectric polymer such as polysulfone (PSF) and high energy density polymer such as poly(vinylidene fluoride) (PVDF), are promising for this application, because high temperature tolerance, high energy density, and low loss can be achieved simultaneously. This study explored the reduction of impurity ion conduction loss in PSF/PVDF MLFs (e.g., the dissipation factor is as low as 0.003 at 1 Hz and 100 degrees C) without sacrificing high dielectric constant and high energy density. Various electric poling processes were explored at a temperature slightly below the glass transition temperature (T-g similar to 185 degrees C) of PSF. Compared with pure alternating current (AC) and pure direct current (DC) poling methods, unipolar (DC + AC) poling was found to be the most effective in polarizing impurity ions from the PVDF layers into the PSF layers. Because of the low segmental mobility below T-g, impurity ions were largely "locked" in PSF. The immobilization of impurity ions was thermally stable up to 120 degrees C. Because DC-link capacitors work with unipolar charge and discharge processes, these PSF/PVDF MLFs with low dielectric losses are promising for the application of advanced power electronics for the automobile industry.

Poly(ε-caprolactone) (PCL)-based nanomaterials, such as nanoparticles and liposomes, have exhibited great potential as controlled release systems, but the difficulties in large-scale fabrication limit their practical applications. Among the various methods being developed to fabricate polymer nanosheets (PNSs) for different applications, such as Langmuir-Blodgett technique and layer-by-layer assembly, are very effort consuming, and only a few PNSs can be obtained. In this paper, poly(ε-caprolactone)-based PNSs with adjustable thickness are obtained in large quantity by simple water exposure of multilayer polymer films, which are fabricated via a layer multiplying coextrusion method. The PNS is also demonstrated as a novel controlled guest release system, in which release kinetics are adjustable by the nanosheet thickness, pH values of the media, and the presence of protecting layers. Theoretical simulations, including Korsmeyer-Peppas model and Finite-element analysis, are also employed to discern the observed guest-release mechanisms.

There is a need for polymeric capacitors with improved energy storage density and thermal stability. In this work, the effect of polymer molecular structure and symmetry on T-g, breakdown strength, and relative permittivity were investigated. A systematic series of four amorphous poly(arylene ether ketone)s were compared. Two of the polymers had symmetric bisphenols while the remaining two had asymmetric bisphenols. Two contained trifluoromethyl groups while the other two had methyl groups. The symmetric polymers had T-g's of approximately 160 degrees C while the asymmetric polymers showed higher T-g's near 180 degrees C. The symmetric polymers had breakdown strengths near 380 kV/mm at 150 degrees C. The asymmetric counterparts had breakdown strengths near 520 kV/mm even at 175 degrees C, with the fluorinated polymers performing slightly better in both cases. The non-fluorinated polymers had higher relative permittivities than the fluorinated materials, with the asymmetric polymers being better in both cases. (C) 2015 Elsevier Ltd. All rights reserved.

Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications.

ABSTRACTA new polymer nanolayer gradient refractive index (GRIN) system with more robust thermal stability because of incorporation of a high glass transition temperature polyester, OKP4HT, was demonstrated. A combination of extruded nanolayered GRIN film systems, comprised of five unique polymer materials, were combined to produce laminate optics comprised of a large internal refractive index gradient distribution, n = 1.445 – 1.630, without degradation of optical transmissive properties. The optical performance of a series of varied magnitude GRIN lenses, ranging from Δn = 0 to 0.185, was evaluated. Increasing the lens refractive index range resulted in decreased optic sphericalaberrations that followed analytical predictions. An analytical approach was reported to correlate the polymer material upper service temperature (UST) to the onset of polymer material loss modulus as measured by DMTA. Thermo‐optical interferometry measurements of irreversible lens deformation confirmed the lenses UST at 125°C for the OKP4HT/PC system as compared to 75°C for a PMM/SAN17 system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42741.

Optical data storage has been widely used in certain consumer applications owing to its passive and robust nature, but has failed to keep with larger industry data storage needs due to the lack of capacity. Many alternatives have been proposed and developed, such as 3D data storage using two-photon absorption that require complex and dangerous laser systems to localize the bits. In this paper, we present a method for localizing bits using a CW 405nm laser diode, in a multilayered polymer film. Data is stored by photobleaching a fluorescent dye, and the response of the material is nonlinear, despite the CW laser and absorption in the visible region. This is achieved using sub-mu s pulses from the laser initiating a photothermal effect. This writing method, along with the inexpensive roll-to-roll method for making the disc, will allow for terabyte-scale optical discs using conventional commercial optics and lasers.

Abstract Co-extruded films with up to 65 layers of two rheologically mismatched polymer systems – polystyrene/poly(methylmethacrylate) (PS/PMMA) and hard/soft thermoplastic polyurethanes (TPUs) – were successfully produced using a combination of a 9-layer feedblock, low-pressure drop multiplier dies, and external lubricants. Formation of viscoelastic instabilities was studied using a custom visualization and by finite element method (FEM) simulations of a standard multiplier. The results showed that the flow inside the standard multiplier die is highly non-uniform, with severe gradients in shear and normal stresses and viscous encapsulation occurring mainly in the initial multiplication stages where there is enough material available in the low-viscosity layers to proceed with the encapsulation. To mitigate layer degradation the standard 2- or 3-layer feedblock was replaced with a 9-layer one, thereby decreasing the thickness of each layer at the end of the feedblock. Also, subsequent layering was performed using a low flow resistance die. This new multiplier die yields a more uniform flow profile and imparts a more homogeneous thermo-mechanical history on the melt which results in an improved layer stability. Simulations showed that in the standard die the second normal-stress difference (N2) responsible for elastic instabilities at the edges of the die are very high. These can be reduced by inducing slip at the wall resulting in be much improved layer uniformity and stability. This was accomplished experimentally via the use of external lubricants, and the resulting layered structure was indeed much better than was possible to achieve with the conventional multiplier dies.

The long-term dielectric lifetime properties of multilayered polycarbonate/poly(vinylidene fluoride-co-hexafluoropropylene) [PC/P(VDF-HFP)] films were measured as a function of the layer thickness. An optimum layer thickness of 160 nm was determined with the longest dielectric lifetime. The morphology of the damaged sites after dielectric breakdown was examined using scanning electron microscope. Acoustic emission detection system was coupled with the dielectric setup to correlate fracture events and dielectric breakdown to thereby elucidate the mechanisms of the enhancements in dielectric lifetime properties. Two types of acoustic signals were always observed during the breakdown process for multilayered films. The high-amplitude signals were attributed to the formation of breakdown pinholes caused by the primary discharge from top to bottom electrode. The subsequent low-amplitude signals were attributed to internal discharges that could further damage the film. The total number of acoustic hits, in particular, low-amplitude hits, increased with decreasing layer thickness, indicating more internal discharges occurred along the layered interface. It was concluded that the breakdown event initiated at a defect initiated “hotspot” formed because of internal pressure buildup. The film was punctured when the pressure buildup inside the film overcame the mechanical strength of the film. More number of PC layers and layer interfaces were desirable to slow down and divert the damage propagation through the film thickness direction. The crazes in P(VDF-HFP) can, however, easily propagate across PC layers with less than 160 nm layer thickness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39877.

ABSTRACTUnique three‐component multilayer films with ATBTATBTA configuration were fabricated using forced assembly multilayer coextrusion for novel dielectric systems. The dielectric breakdown strength, displacement–electric field hysteresis, and dielectric spectroscopy of 65‐layer polycarbonate (PC)/tie/poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐HFP)) were investigated with various tie materials. Three different tie materials, poly(methyl methacrylate) (PMMA), styrene‐co‐acrylonitrile copolymer with 30% acrylonitrile content (SAN30), and poly(ethylene terephthalate‐co‐1,4‐cycohexanedimethylene terephthalate) (PETG) were chosen owing to their various degrees of interaction with either P(VDF‐HFP) or PC. The 65‐layer PC/PMMA/P(VDF‐HFP) films exhibited a 25% enhancement in breakdown properties, 50% higher energy density, 40% smaller hysteresis loop areas, and orders of magnitude slower ion migration relative to the 33‐layer PC/P(VDF‐HFP) control. These property improvements are mainly attributed to the localized interactions at PMMA/P(VDF‐HFP) and PMMA/PC interfaces, forming interphase regions. The modified PMMA/P(VDF‐HFP) interphase region can effectively hinder the migration of impurity ions in P(VDF‐HFP), reducing their mobility within the layer. Additionally, a small fraction of PMMA can lead to slightly increased dielectric constant of the composite films owing to strong interaction between PMMA and P(VDF‐HFP). The other two systems with PETG and SAN30 as tie layers exhibited marginal improvements in dielectric properties owing to their weaker interactions with the P(VDF‐HFP) layers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 978–991

A nanolayered polymer films approach to designing and fabricating gradient refractive index (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry have been demonstrated to produce a new class of optics. This approach utilized nanolayered polymer materials, constructed with polymethylmethacrylate and a styrene-co-acrylonitrile copolymer with a tailorable refractive index intermediate to bulk materials, to fabricate discrete GRIN profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is reviewed. A collection of technology-demonstrating previously reported nanolayered GRIN case studies is presented that include: (1) the optical performance of a f/# 2.25 spherical GRIN plano-convex singlet with one quarter (2) the weight of a similar BK7 lens and a bio-inspired aspheric human eye GRIN lens. Original research on the fabrication and characterization of a Luneburg inspired GRIN ball lens is presented as a developing application of the nanolayered polymer technology. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

We report the preparation of the uni-axially aligned nanofibers containing poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) or poly(3-hexylthiophene) (P3HT) using the electrospinning technique. The emission anisotropy of the aligned conjugated polymer nanofibers was investigated using the luminescence polarization spectroscopy. The results revealed that the photoluminescence of the aligned nanofibers was highly anisotropic with stronger emission along the nanofiber axis; in contrast, the photoluminescence of random nanofibers and thin films showed weak emission anisotropy. These results suggested that the electrospun conjugated polymer nanofibers had macromolecular chains preferably oriented along the nanofiber axis. The study provides new guidance in the development of unique optoelectronic devices based on electrospun nanofibers of conjugated polymers.

We report the effects of surface modification on the fluorescence properties of conjugated polymer/zinc oxide nanocomposites. Zinc oxide nanoparticle surface was partially capped by poly(vinylpyrolidone) (PVP) during hydrolysis of zinc acetate dihydrate in methanol in ambient condition. The ZnO-capped nanoparticles were characterized by XRD and TEM. The fluorescence properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/ZnO nanocomposites with different mass ratios were studied by steady-state and time-resolved spectroscopy. The results indicate that the surface-modified ZnO nanoparticles are more effective to quench the emission of MEH-PPV by charge transfer process than the non-capped ZnO. The more effective charge transfer in MEH-PPV/ZnO-capped is attributed to the better dispersion of the nanoparticles in MEH-PPV matrix and THF solvent.