Metallized polyimide polymer films are of interest owing to their wide scope of applications including adaptive optical mirrors, solar dynamic power generation, radiation shielding, and thermal control coatings. Palladium-based polyimide films have proven to be unique in terms of thermal reduction, photochemistry and nanoparticulate distribution within the polymer matrix. When Pd polyamic acid is exposed to lamp radiation for 15 hours prior to curing, an additional nanoscale metallic interlayer is created within the surface-metallized polyimide matrix. This photo-process creates alternating nanoparticulate layers of palladium metal. Whilst previous efforts have produced metallic interlayer in 15 hours, we show that an excimer laser reduces this time to 4-8 minutes. Preliminary results using a femtosecond laser show that a metal interlayer can be formed with as little as 8 seconds of exposure time. Transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) are used to characterize the layers. In addition to Pd, surface metallization and interlayer formation using other metals is discussed.

We recently fabricated and characterized a new class of multilayer dielectric elastomer films comprising alternating layers of two different polymers, at least one of which is an elastomer. The films discussed here contain THV (a terpolymer of poly(vinylidene fluoride)) and poly(ethylene octene) [EO] elastomer. The multilayer structure provides improved dielectric and electromechanical performance relative to monolithic films of THV or EO. These properties are controlled by the composition and the layer structure. For example, increasing the concentration of the elastomeric EO component increases the maximum axial strain (sz). Layering EO with THV also increases the breakdown strength (EB ∼ 265 - 300 V/µm) relative to monolithic EO (EB ∼ 150 V/µm) or THV (EB ∼ 245 V/µm) control films. This enhancement in breakdown strength is consistent with a barrier effect that is also observed in multilayer polymer capacitor films. The increase in breakdown strength allows 512-layer 75 vol% EO / 25 vol% THV films to achieve maximum axial strains of sz nearly 4%, higher than can be attained by either EO or THV films alone. In addition, layering reduces remnant strain and electromechanical hysteresis by limiting the effective field within the THV layers. The 75% EO/ 25% THV films show robust operational longevity with little loss in axial strain when subjected to repeated actuation at Emax = 225 V/µm (producing sz = 2.2%). Under these conditions, we observe 3,000 consecutive actuation cycles with no electrical breakdown. In comparison, single component EO control films undergo electrical breakdown at this field and THV control films survive only a few hundred actuation cycles under these conditions. The results demonstrate that multilayering is an effective technique to increase the dielectric strength of elastomer materials and in turn improve upon strain and operational longevity (repeated actuation cycles) characteristics.

Nanofiber-based membranes were prepared by two different methods for use as separators for Lithium-ion batteries (LIBs). In the first method, Electrospinning was used for the fabrication of Polyvinylidene fluoride PVDF nanofiber coatings on polyolefin microporous membrane separators to improve their electrolyte uptake and electrochemical performance. The nanofiber-coated membrane separators show better electrolyte uptake and ionic conductivity than that for the uncoated membranes. In the second method, Forcespinning® (FS) was used to fabricate fibrous cellulose membranes as separators for LIBs. The cellulose fibrous membranes were made by the Forcespinning® of a cellulose acetate solution precursor followed by a subsequent alkaline hydrolysis treatment. The results show that the fibrous cellulose membrane-based separator exhibits high electrolyte uptake and good electrolyte/electrode wettability and therefore can be a good candidate for high performance and high safety LIB separators.

Precise spatial patterns and micro and nanostructures of peptides and proteins have widespread applications in tissue engineering, bioelectronics, photonics, and therapeutics. Optical lithography using proteins provides a route to directly fabricate intricate, bio-friendly architectures rapidly and across a range of length scales. The unique mechanical strength, optical properties, biocompatibility and controllable degradation of biomaterials from silkworms offer several advantages in this paradigm. Here, we present the biochemical synthesis and applications of a “protein photoresist” synthesized from the silk proteins, fibroin and sericin. Using light-activated direct-write processes such as photolithography, we show how silk proteins can form high resolution, high fidelity structures in two and three dimensions. Protein features can be precisely patterned at sub-microscale resolution (µm) at the bench-top over macroscale areas (cm), easily and repeatedly with high-throughput. For instance, periodic, microstructured arrays can be patterned over large areas to form structurally induced iridescent patterns and functional opto-electronic structures. We further demonstrate how photocrosslinked protein micro-architectures can function for the spatial guidance of cells without use of cell-adhesive ligands as biocompatible and biodegradable scaffolds. The ease of biochemical functionalization, biocompatibility, as well as favorable mechanical properties and biodegradation of this silk biomaterial provide opportunities for otherwise inaccessible applications as sustainable, bioresorbable protein microdevices.