We report recent progress in the development of low modulus, highly electrically conducting thin film sheet and fabric materials and devices formed by molecular-level self-assembly processing methods and their use in flexible circuits.
This paper summarizes nanostructured optical fiber sensors fabricated by molecular self-assembly chemistry. Strain, pressure, vibration and chemical sensors are described which are based on selfassembled fiber cores, claddings, distal endface coatings and free-standing membranes.
We discuss recent improvements of Metal RubberTM materials formed by electrostatic self-assembly (ESA) processing. Free-standing and mechanically robust sheets of Metal RubberTM have been synthesized with electrical conductivities approximately one order of magnitude lower than those of bulk noble metals and with moduli from 1 to 100 MPa.
We report recent improvements of Metal RubberTM strain sensors formed by electrostatic self-assembly (ESA) processing. The sensors may be used to measure strains from approximately 1 microstrain to several hundred percent strain, over gauge lengths ranging from approximately 1 millimeter to several tens of centimeters.
This paper describes the use of Metal Rubber, which is an electrically conductive, low modulus, and optically transparent free-standing nanocomposite, as an electrode for active polymer devices. With its controllable and tailorable properties [such as modulus (from ~ 1 MPa to 100 MPa), electrical conductivity, sensitivity to flex and strain, thickness, transmission, glass transition, and more], Metal Rubber exhibits massive improvements over traditional stiff electrodes that physically constrain the actuator device motion and thus limit productivity. Metal Rubber shows exceptional potential for use as flexible electrodes for many active polymer applications.
This paper describes the commercial applications of Metal Rubber, the first material of its kind, a self-assembled free-standing electrically conductive elastomer in biomedical, aerospace and microelectronic areas. Metal Rubber is a novel nanocomposite formed via the self-assembly processing of metal nanoparticles and elastomeric polyectrolytes. This type of processing allows for control over bulk mechanical and electrical properties and requires only ppm quantities of metal to achieve percolation. The use of nanostructured precursors also results in transparent, electrically conductive nanocomposites. Metal Rubber elastomers are being developed as electrodes, for biomedical applications; flexible interconnects for microelectronics, and sensors to detect fatigue, impact and large strain for aerospace applications. This novel material may be formed as a conformal coating on nearly any substrate or as free standing films.
This paper describes improvements that have been made in optical fiber biosensors based on thin films deposited onto the ends of optical fiber waveguides using molecular-level self-assembly processes. The properties of the sensor films may be varied by controlling both the chemistry and the morphology and ordering of the films during their fabrication. For example, multilayer segments of films having different indices of refraction may be deposited to form quarter wavelength stack filters whose reflection properties change as a function of concentration of target chemical that modifies the index of the outermost layer or layers. Prior work has shown that by using different chemicals in the self-assembled layers, correspondingly different target chemicals may be detected. These have included water vapor, ammonia, dichloromethane and others. Improvements have been made in the range of index of refraction that may be achieved in the individual layer segments, specifically over the range of 1.2 to 1.8 at visible and near-infrared wavelengths. This paper shows how such an improvement in index difference influences the minimum detectable chemical concentration difference detectable using this approach.
This paper presents an update concerning the properties of a new class of nanostructured materials that exhibit the combined properties of low mechanical modulus and high electrical conductivity. Such "Metal Rubber<sup>TM</sup>" materials are formed by molecular-level self-assembly processes. Material synthesis and properties are described. Potential applications for space-based photonics and electronics are in flexible polymer-based electrodes and opto-electronic devices.
We report the development of nanostructured strain sensors formed by electrostatic self-assembly (ESA) processing. The sensors may be used to measure strains from 1 microstrain to more than 100% strain, over gauge lengths ranging from approximately 1 millimeter to tens of centimeters.
We report the development of low modulus, highly conducting thin film electrodes formed by molecular-level self-assembly processing methods. The electrodes may be used on sensor or actuator materials requiring large strain.
We report improvements of an optical fiber-based humidity sensor to the problem of breathing diagnostics. The sensor is fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclusters into multilayered optical thin films on the cleaved and polished flat end of a singlemode optical fiber. Recent work has studied the synthesis process and the fundamental mechanisms responsible for the change in optical reflection from such a multicomponent film that occurs as a function of humidity and various chemicals. We briefly review that prior work as a way to introduce more recent developments. The paper then discusses the application of these humidity sensors to the analysis of air flow associated with breathing . We have designed the sensor thin film materials to enable the detection of relative humidity over a wide range, from approximately 5 to 95%, and for response times as short as several microseconds. This fast response time allows the near real-time analysis of air flow and water vapor transport during a single breath, with the advantage of very small size. The use of multiple sensors spaced a known distance apart allows the measurement of flow velocity, and recent work indicates a variation in sensor response versus coating thickness.
A simple optical fiber-based strain and pressure sensor has been fabricated using nanostructured self-assembled elastomeric free-standing thin film materials. The fabrication of the sensor material and a demonstration of the sensor performance are described.
We report recent developments in the design and fabrication of molecularly self-assembled thin film materials that may be incorporated with optical fiber waveguides to form humidity and other gas sensors of use in biomedical diagnositc systems. Optical fiber distal end sensors based on this concept may be fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclustesr into multilayered optical thin films on the cleaved and polished flat ends of singlemode optical fibers. Prior work reported at this meeting has studied the synthesis process and sensor dynamics, including sensor 10-90% risetime on the order of microseconds. This paper briefly reviews that work but then reports new developments in the synthesis of the sensor films.