NanoSonic has designed and produced a multifunctional material having low air permeability, cryogenic flexibility, and
self-healing capabilities as a candidate bladder for expandable vehicles and habitats deployed during space missions.
This innovative self-healing mechanism is accomplished rheologically, rather than chemically, which allows for
immediate self-sealing under reduced pressure encountered during space explorations. Investigations were conducted in
collaboration with NASA Johnson Space Center (JSC), Colorado State University (CSU) and the NASA Space
Radiation Laboratory (NSRL). These initial studies were designed to evaluate tolerance to damage from exposure to
ionizing radiations that simulated heavy ion components of Galactic Cosmic Rays (GCR) and high doses from solar
protons. Results verified that these composites maintain durability using tests for air permeability, self-sealing following
puncture, and sustained mechanical strength with minimal loss in elasticity upon cryogenic flexure.
This paper describes the development and testing of Metal Rubber sensors for the nondestructive, normal force detection of ice accretion on aerospace structures. The buildup of ice on aircraft engine components, wings and rotorblades is a problem for both civilian and military aircraft that must operate under all weather conditions. Ice adds mass to moving components, thus changing the equations of motion that control the operation of the system as well as increasing drag and torque requirements. Ice also alters the surface geometry of leading edges, altering the airflow transition from laminar to turbulent, generating turbulence and again increasing drag. Metal Rubber is a piezoresistive material that exhibits a change in electrical resistance in response to physical deformation. It is produced as a freestanding sheet that is assembled at the molecular level using alternating layers of conductive metal nanoparticles and polymers. As the volume percentage of the conductive nanoparticle clusters within the material is increased from zero, the onset of electrical conduction occurs abruptly at the percolation threshold. Electrical conduction occurs due to electron hopping between the clusters. If a length of the material is strained, the clusters move apart so the efficiency of electron hopping decreases and electrical resistance increases. The resulting change in resistance as a function of the change in strain in the material, at a specific volume percentage of conductive clusters, can be interpreted as the transduction response of the material. We describe how sensors fabricated from these materials can be used to measure ice buildup.
This paper summarizes work in the molecular-level self-assembly of two-dimensional and three-dimensional materials. Synthesis processes are briefly discussed, and examples of multiple properties achievable in two-dimensional and three-dimensional self-assembled materials are given.
NanoSonic of Blacksburg, VA, is a university research center spin-off company whose business story forms a chapter in a new SPIE Press book, Engineering a High-Tech Business: Entrepreneurial Experiences and Insights. Two NanoSonic founders describe the creation and early growth of the company in this excerpt.
Recent work in the fabrication of self assembled quantum dot (QD) detectors for optical fiber sensors is reported in this
paper. The ability to develop the QD based devices and materials via the electrostatic self-assembly (ESA) process has
been demonstrated. The QD precursor nanocluster materials involved in ESA have been designed and synthesized to
proper size, stabilized in an aqueous-based solution, and functionalized to allow self-assembly. The optical fiber sensor
instrumentation has been developed to monitor the reflected optical power with the buildup of the QD layers on the fiber
endface during the ESA process. The results are confirmed by observing the effects of low-finesse QD Fabry-Perot
interferometric cavities formed via such processes on the ends of optical fibers. The photocurrent-voltage characteristics
show a diode-like behavior with linear photocurrent in the reverse bias and nonlinearity in the forward bias. It is
suggested that fast response times can be achieved due to the high carrier mobilities that arise in part due to structure of
the materials formed via the solution-based ESA process.
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.
Recent work in the fabrication of self assembled quantum dot (QD) detectors on active structural fibers and
for the implementation of optical fiber sensors is reported in this paper. The ability to develop the QD
based devices and materials via the electrostatic self-assembly (ESA) process has been demonstrated by
Hand and Kang in prior work. The QD precursor nanocluster materials involved in ESA have been
designed and synthesized to proper size, stabilized in an aqueous-based solution, and functionalized to
allow self-assembly. Optical fiber sensor instrumentation has been developed to monitor the reflected
optical power with the buildup of the QD layers on the fiber endface during the ESA process. The results
are confirmed by observing the effects of low-finesse QD Fabry-Perot interferometric cavities formed via
such processes on the ends of optical fibers. The photocurrent-voltage characteristics show a diode-like
behavior with linear photocurrent in the reverse bias and non-linearity in the forward bias. It is suggested
that fast response times can be achieved due to the high carrier mobilities that arise in part due to structure
of the materials formed via the solution-based ESA process. This paper reviews this prior work and shows
examples of deposition of devices on both fiber endfaces and cladding surfaces.
This paper describes the use of Metal RubberTM, which is an electrically-conductive, low modulus, highly-flexible, and optically transparent free-standing or conformal coating nanocomposite material that is fabricated via Electrostatic Self-Assembly (ESA), as a polymer MEMS sensor for actuator materials. ESA is an environmentally-friendly layer-by-layer fabrication technique in which Metal RubberTM can be tailor designed at the molecular level to function as a sensor and/or electrode for active polymer devices. With its controllable and tailorable properties (such as mechanical modulus [from less than 0.1 MPa to greater than 500 MPa], electrical conductivity, sensitivity to flex and strain (tension and compression), thickness, transmission, glass transition, and more), Metal RubberTM exhibits massive improvements over traditional stiff electrodes and sensors (with bulky/heavy wire components) that physically constrain the actuator device motion and thus limit productivity. Metal RubberTM shows exceptional potential for use as flexible sensors, electrodes, and interconnect components for many active polymer applications. One example of such is NanoSonic's Metal RubberTM-Polymer MEMS (MRTM-PMEMS) nanocluster-based corrosion sensor for aircraft coatings that was developed for an Air Force SBIR program. MRTM-PMEMS was tailored via ESA for use as an in-situ sensor of chemical modifications and the breakdown of surface coatings via micro-strain measurements.
Molecular-level self-assembly processes allow the formation of novel materials with properties that are not
achievable using conventional fabrication methods. For example, nanostructured metals and polymers may be combined
to form inorganic/organic materials that exhibit properties typically associated with each of these species separately,
namely high electrical conductivity and low Young's modulus. The combination of such properties is of interest for a
number of engineering applications. For example, methods to form stretchable metal conductors, either on elastomeric
substrates or as free-standing materials, have been investigated for some time, in part as a way to overcome the high
modulus of sensor and actuator electrode materials, and more generally to address the need for mechanically flexible
interconnections in polymer electronic devices, flex circuits, electronic textiles and similar electrical circuit applications.
Of particular recent interest for example is summarized in  where a process to form electrical connectivity using 100
nm-wide gold stripes evaporated onto polydimethylsiloxane (PDMS) is reported, and where non-zero electrical
conductivity was observed for strains up to 22%.
Two different optical fiber-based sensor approaches are compared for the detection of hydrogen gas. The two sensors both use Fabry-Perot techniques that have been investigated for some time for other applications. One involves the use of an Extrinsic Fabry-Perot Interferometric (EFPI) sensor scheme, and the other uses a nanoFabry-Perot (nanoFP) cavity that is formed on the distal end of a fiber endface. It is found in general that the sensitivity of the EFPI sensor is higher than that of the nanoFP, but that its speed of response is slower.
This paper describes the use of free-standing electrically conductive ultra-low modulus materials that withstand elongations up to 1000% as sensors for the measurement of large strains. NanoSonic has developed novel, high performance, multifunctional polymers for use in self-assembly processing that result in durable free-standing conductive films - with both controlled nominal conductivity and Young's modulus. Such films exhibit a change in electrical conductivity as a function of tensile strain; whereby the magnitude of the change is controlled via chemical processing.
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 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 RubberTM" 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 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 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.
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.
This paper reports developments in the molecular-level self-assembly of materials that may be used in photonic devices. Specifically we present results of layer-by-layer electrostatic self-assembly processes that may be used to rapidly form electrically-conductive and optically transparent films for potential use as claddings for electro-optic modulators or other optical waveguiding structures.