Ajit Khosla

A New Low-Temperature Electrochemical Hydrocarbon and NOx Sensor

In this article, a new investigation on a low-temperature electrochemical hydrocarbon and NOx sensor is presented. Based on the mixed-potential-based sensing scheme, the sensor is constructed using platinum and metal oxide electrodes, along with an Yttria-Stabilized Zirconia (YSZ)/Strontium Titanate (SrTiO3) thin-film electrolyte. Unlike traditional mixed-potential sensors which operate at higher temperatures (>400 °C), this potentiometric sensor operates at 200 °C with dominant hydrocarbon (HC) and NOx response in the open-circuit and biased modes, respectively. The possible low-temperature operation of the sensor is speculated to be primarily due to the enhanced oxygen ion conductivity of the electrolyte, which may be attributed to the space charge effect, epitaxial strain, and atomic reconstruction at the interface of the YSZ/STO thin film. The response and recovery time for the NOx sensor are found to be 7 s and 8 s, respectively. The sensor exhibited stable response even after 120 days of testing, with an 11.4% decrease in HC response and a 3.3% decrease in NOx response.

3D printing of shape memory hydrogels with tunable mechanical properties

Utilization of soft material like hydrogels for task-specific applications such as in soft robotics requires freedom in the manufacturing process and designability. Here, we have developed highly robust thermoresponsive poly(dimethyl acrylamide-co-stearyl acrylate and/or lauryl acrylate) (PDMAAm-co-SA and/or LA)-based shape memory gels (SMGs) using a customized optical 3D gel printer. This process enabled rapid and moldless fabrication of SMGs with a variety of shapes and sizes. By varying the compositions of the constituent monomers, a wide variety of SMGs with tunable mechanical, thermal, optical and swelling properties have been obtained. Printed SMGs with excellent fixity and recovery ratios have exhibited a wide range of values of Youngs modulus (0.04-17.35 MPa) and strain (612-2363%) at room temperature when the acrylate co-monomer (SA and LA) content was varied and the value of strain has been found to be enhanced at elevated temperatures. Thermogravimetric analysis (TGA) of the SMGs shows one step peak degradation (407-417 °C) regardless of composition after an initial mass loss due to water evaporation. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) revealed variable transition temperatures (29-49.5 °C) depending on the SA and LA content. SMGs with all of the composition ratios possess high transparency with variable swelling degrees in water and different organic solvents and exhibit refractive index values in the range of intraocular lenses, making them suitable for applications in the optical field. These unique properties of 3D printed SMGs with free formability and tunable properties are expected to generate rapid demand in a variety of sectors in biomedicine, robotics and sensing applications.

Carbon fiber doped thermosetting elastomer for flexible sensors: physical properties and microfabrication

We have developed conductive microstructures using micropatternable and conductive hybrid nanocomposite polymer. In this method carbon fibers (CFs) were blended into polydimethylsiloxane (PDMS). Electrical conductivities of different compositions were investigated with various fiber lengths (50–250 μm), and weight percentages (wt%) (10–60 wt%). Sample composites of 2 cm × 1 cm × 500 μm were fabricated for 4-point probe conductivity measurements. The measured percolation thresholds varied with length of the fibers: 50 wt% (307.7 S/m) for 50 µm, 40 wt% (851.1 S/m) for 150 µm, and 30 wt% (769.23 S/m) for 250 μm fibers. The conductive composites showed higher elastic modulus when compared to that of PDMS.

Development of multi-material 3D printer

We are developing a Multi Material 3D printer to print an object with different kind of soft and hard material in a single run. It is expected that the combination of printing soft and hard material will be a new kind of 3D printer. Our main printing material is conductive based soft filament made by our laboratory “Soft and Wet Matter Engineering Laboratory”, other different soft filament and hard plastic filament to create fully functional, multi material objects in a single printing run with greater variety and lower cost than other single material printing. In addition, we are developing a special type of Extruder, by using this we will be able to print both soft and hard material with one printer. This will be a new era of 3D printer. Such kind of 3D printer will possibly be a good STEM tool in medical sector and robotics.

Ionic liquid in 3D printing (Conference Presentation)

Ionic liquids (ILs) are fascinating materials with unique physicochemical properties like non-volatility, non-flammability, wide electrochemical window, high thermal stability and high ionic conductivity. They offer numerous possibilities in the fields ranging from electrochemistry to mechanical engineering however their employment in the 3D printing technology is very limited till to date. One of the big challenges of using 3D printing for materials is a careful selection of component material with a perfect concentration and an appropriate method. In this study, we focused on the potential of ILs on 3D printing technology covering the most popular printing methods named fused deposition modeling (FDM) and stereolithography (SLA) process. For FDM process IL-based conductive nanocomposite filaments have been developed and printed via 3D printing process along with their material characterization. In a different approach, ionic gels in IL medium have been successfully printed by SLA process with precise structures of microscale resolution. Conductive, mechanical and other physicochemical properties have been explored to get the proper understanding of the ionic gel materials.

Poly ionic liquid-based nano composites for smart electro-mechanical devices

Conducting polymer composites become increasingly significant for variety of applications in electrical and mechanical devices. Poly (ionic liquid)s (PILs) achieved remarkable interest in this field for the unique properties and added advantages in mechanical stability, improved processability, durability, and spatial controllability. Carbon nanotube (CNT) as filler material to the matrix of PIL can achieve the desired composite material with improved electrical and mechanical properties. In this work, we developed PIL-CNT nanocomposites by using quaternary ammonium type IL monomer and multiwall CNT. Their mechanical, thermal and thermomechanical properties have been studied and future possibilities of employing in electromechanical devices have been explored.

3D printing in social education: Eki-Fab and student PBL

Additive manufacturing or 3D printer is one of the most innovative material processing methods. We are considering that human resources for 3D printing would be needed in the future. To educate the abilities of the digital fabrication, we have the public digital fabrication space “Eki-Fab” for junior and high school students and Project Based Learning (PBL) class for undergraduate students. Eki-Fab is held on every Saturday at the Yonezawa train station. In the “Eki-Fab”, anybody can study the utilizing of 3D printer and modeling technics under the instruction of staff in Yamagata University. In the PBL class, we have the class every Thursday. The students get the techniques of the digital fabrication through the PBL.

Micro-Nano Systems in Health Care and Environmental Monitoring

This focus issue is devoted to Micro-Nano Systems in Health Care and Environmental Monitoring. It has been an exciting opportunity to collect together papers from invited speakers and authors who participated in the related symposium held at the 227th ECS meeting in Chicago in May 2015. This meeting brought together medical professionals, clinicians, engineers, chemists, biologists and physicists under the same roof. This symposium and the papers published in the focus issue provide for a synopsis of the research, development, and technological evolution of micro-nano sensors and systems in healthcare and environmental monitoring applications.