Printing Highly Controlled Suspended Carbon Nanotube Network on Micro-patterned Superhydrophobic Flexible Surface

Superhydrophobic Polymer Composite Surfaces Developed via Photopolymerization

Fabrication of superhydrophobic materials using incumbent techniques involves several processing steps and is therefore either quite complex, not scalable, or often both. Here, the development of superhydrophobic surface-patterned polymer-TiO₂ composite materials using a simple, single-step photopolymerization-based approach is reported. The synergistic combination of concurrent, periodic bump-like pattern formation created using irradiation through a photomask and photopolymerization-induced nanoparticle (NP) phase separation enables the development of surface textures with dual-scale roughness (micrometer-sized bumps and NPs) that demonstrate high water contact angles, low roll-off angles, and desirable postprocessability such as flexibility, peel-and-stick capability, and self-cleaning capability. The effect of nanoparticle concentration on surface porosity and consequently nonwetting properties is discussed. Large-area fabrication over an area of 20 cm², which is important for practical applications, is also demonstrated. This work demonstrates the capability of polymerizable systems to aid in the organization of functional polymer-nanoparticle surface structures.

Ionization Gas Sensor using Suspended Carbon Nanotube Beams

An ionization sensor based on suspended carbon nanotubes (CNTs) was presented. A suspended CNT beam was fabricated by a low-temperature surface micromachining process using SU8 photoresist as the sacrificial layer. Application of a bias to the CNT beam generated very high non-linear electric fields near the tips of individual CNTs sufficient to ionize target gas molecules and initiate a breakdown current. The sensing mechanism of the CNT ionization sensor was discussed. The sensor response was tested in air, nitrogen, argon, and helium ambients. Each gas demonstrated a unique breakdown signature. Further, the sensor was tested with gaseous mixtures. The sensor exhibited good long-term stability and had comparable performance to other reported CNT-based ionization sensors in literature, which use high-temperature vapor deposition methods to grow CNTs. The sensor notably allowed for lower ionization voltages due to its reduced ionization gap size.

The Semiconductor/Conductor Interface Piezoresistive Effect in an Organic Transistor for Highly Sensitive Pressure Sensors

The piezoresistive pressure sensor, a kind of widely investigated artificial device to transfer force stimuli to electrical signals, generally consists of one or more kinds of conducting materials. Here, a highly sensitive pressure sensor based on the semiconductor/conductor interface piezoresistive effect is successfully demonstrated by using organic transistor geometry. Because of the efficient combination of the piezoresistive effect and field-effect modulation in a single sensor, this pressure sensor shows excellent performance, such as high sensitivity (514 kPa^-1 ), low limit of detection, short response and recovery time, and robust stability. More importantly, the unique gate modulation effect in the transistor endows the sensor with an unparalleled ability-tunable sensitivity via bias conditions in a single sensor, which is of great significance for applications in complex pressure environments. The novel working principle and high performance represent significant progress in the field of pressure sensors.

Suspended Carbon Nanotubes for Humidity Sensing

A room temperature microfabrication technique using SU8, an epoxy-based highly functional photoresist as a sacrificial layer, is developed to obtain suspended aligned carbon nanotube beams. The humidity-sensing characteristics of aligned suspended single-walled carbon nanotube films are studied. A comparative study between suspended and non-suspended architectures is done by recording the resistance change in the nanotubes under humidity. For the tests, the humidity was varied from 15% to 98% RH. A comparative study between suspended and non-suspended devices shows that the response and recovery times of the suspended devices was found to be almost 3 times shorter than the non-suspended devices. The suspended devices also showed minimal hysteresis even after 10 humidity cycles, and also exhibit enhanced sensitivity. Repeatability tests were performed by subjecting the sensors to continuous humidification cycles. All tests reported here have been performed using pristine non-functionalized nanotubes.

Ultrafast structural evolution and formation of linear carbon chains in single-walled carbon nanotube networks by femtosecond laser irradiation

Inter-allotropic structural transformation of sp² structured nanocarbon is a topic of fundamental and technological interest in scalable nanomanufacturing. Such modifications usually require extremely high temperature or high-energy irradiation, and are usually a destructive and time-consuming process. Here, we demonstrate a method for engineering a molecular structure of single-walled carbon nanotubes (SWNTs) and their network properties by femtosecond laser irradiation. This method allows effective coalescence between SWNTs, transforming them into other allotropic nanocarbon structures (double-walled, triple-walled and multi-walled nanotubes) with the formation of linear carbon chains. The nanocarbon network created by this laser-induced transformation process shows extraordinarily strong coalescence induced mode in Raman spectra and two-times enhanced electrical conductivity. This work suggests a powerful method for engineering sp² carbon allotropes and their junctions, which provides possibilities for next generation materials with structural hybridization at the atomic scale.

Measuring Interfacial Adhesion of Carbon Nanotube Bundles and Electrospun Polymer Fibers

Adhesion at the dissimilar interface of single wall carbon nanotube (SWCNT) bundles and electrospun polymer nanofibers (Espun) was directly measured using a nano cheese cutter. A sample fiber suspended at the tip of an atomic force microscope cantilever and another freestanding fiber on a mica substrate were arranged in a cross-cylinder configuration and allowed to adhere. External tensile load led to spontaneous detachment or "pull-off". Adhesion was shown to be dominated by van der Waals attraction, and the detachment process conforms to the classical Maugis parameter in the JKR-DMT transition.