Chandramouli Subramaniam

One hundred fold increase in current carrying capacity in a carbon nanotube-copper composite

Increased portability, versatility and ubiquity of electronics devices are a result of their progressive miniaturization, requiring current flow through narrow channels. Present-day devices operate close to the maximum current-carrying-capacity (that is, ampacity) of conductors (such as copper and gold), leading to decreased lifetime and performance, creating demand for new conductors with higher ampacity. Ampacity represents the maximum current-carrying capacity of the object that depends both on the structure and material. Here we report a carbon nanotube–copper composite exhibiting similar conductivity (2.3–4.7 × 105 S cm−1) as copper (5.8 × 105 S cm−1), but with a 100-times higher ampacity (6 × 108 A cm−2). Vacuum experiments demonstrate that carbon nanotubes suppress the primary failure pathways in copper as observed by the increased copper diffusion activation energy (∼2.0 eV) in carbon nanotube–copper composite, explaining its higher ampacity. This is the only material with both high conductivity and high ampacity, making it uniquely suited for applications in microscale electronics and inverters.

Influence of matching solubility parameter of polymer matrix and CNT on electrical conductivity of CNT/rubber composite

We report a general approach to fabricate elastomeric composites possessing high electrical conductivity for applications ranging from wireless charging interfaces to stretchable electronics. By using arbitrary nine kinds of rubbers as matrices, we experimentally demonstrate that the matching the solubility parameter of CNTs and the rubber matrix is important to achieve higher electrical conductivity in CNT/rubber composite, resulting in continuous conductive pathways leading to electrical conductivities as high as 15 S/cm with 10 vol% CNT in fluorinated rubber. Further, using thermodynamic considerations, we demonstrate an approach to mix CNTs to arbitrary rubber matrices regardless of solubility parameter of matrices by adding small amounts of fluorinated rubber as a polymeric-compatibilizer of CNTs. We thereby achieved electrical conductivities ranging from 1.2 to 13.8 S/cm (10 vol% CNTs) using nine varieties of rubber matrices differing in chemical structures and physical properties. Finally, we investigated the components of solubility parameter of CNT by using Hansen solubility parameters, these findings may useful for controlling solubility parameter of CNTs.

CHEMICAL INTERACTIONS AT NOBLE METAL NANOPARTICLE SURFACES — CATALYSIS, SENSORS AND DEVICES

In this paper, a summary of some of the recent research efforts in our laboratory on chemical interactions at noble metal nanoparticle surfaces is presented. The article is divided into five sections, detailing with (i) interactions of simple halocarbons with gold and silver nanoparticle surfaces at room temperature by a new chemistry and the exploitation of this chemistry in the extraction of pesticides from drinking water, (ii) interaction of biologically important proteins such as Cyt c, hemoglobin and myoglobin as well as a model system, hemin with gold and silver nanoparticles and nanorods forming nano–bio conjugates and their surface binding chemistry, (iii) formation of polymer–nano composites with tunable optical properties and temperature sensing characteristics by single and multi-step methodologies, (iv) nanomaterials-based flow sensors and (v) composites of noble metal nanoparticles and metallic carbon nanotubes showing visible fluorescence induced by metal–semiconductor transition.

Nanoparticles-chemistry, new synthetic approaches, gas phase clustering and novel applications

In this paper, an overview of the synthesis, chemistry and applications of nanosystems carried out in our laboratory is presented. The discussion is divided into four sections, namely (a) chemistry of nanoparticles, (b) development of new synthetic approaches, (c) gas phase clusters and (d) device structures and applications. In ‘chemistry of nanoparticles’ we describe a novel reaction between nanoparticles of Ag and Au with halocarbons. The reactions lead to the formation of various carbonaceous materials and metal halides. In ‘development of new synthetic approaches’ our one-pot methodologies for the synthesis of core-shell nanosystems of Au, Ag and Cu protected with TiO2 and ZrO2 as well as various polymers are discussed. Some results on the interaction of nanoparticles with biomolecules are also detailed in this section. The third section covers the formation of gas phase aggregates/clusters of thiol-protected sub-nanoparticles. Laser desorption of H2MoO4, H2WO4, MoS2, and WS2 giving novel clusters is discussed. The fourth section deals with the development of simple devices and technologies using nanomaterials described above.

Real-Time, Wearable, Biomechanical Movement Capture of Both Humans and Robots with Metal-Free Electrodes

We demonstrate an all-carbon-based, flexible, conformal movement-capturing device capable of precisely monitoring biomechanical movements of both humans and robots. Mechanically robust, metal-free electrodes form a unique component of the device responsible for qualitatively and quantitatively transducing biomechanical movements without any signal artifacts. Importantly, the device withstands and operates in a wide dynamic range for both stretching (25% strain) and bending (140°) actions with minimal cycling hysteresis (2.0), high repeatability (>100 cycles), low creep, and humidity-independent rapid response (∼200 ms). Furthermore, the device qualitatively distinguishes movements such as bending of finger, knuckle, and wrist and also provides quantitative information on the extent of such movements. We establish that single-wall carbon nanotubes (CNTs) embedded in ultralow concentration (0.016 wt %) within an elastomeric matrix undergo three-dimensional conformational changes during biomechanical movements that are subsequently transduced as signals. In addition, such CNT–elastomer strips exhibit enhanced stretchability (>100%) and elasticity (∼77%) in comparison to those of pure elastomers, leading to a wider dynamic working range of the device. Furthermore, seamless integration of a versatile gesture tracker on ubiquitous platforms, such as human skin, kinesiologic tapes, gloves, and robotic arms, is achieved, thereby catering to applications ranging from healthcare monitoring and physiotherapy to robotics and wearable technologies.