The field of printable electronics has been experiencing increased interest and growth to meet the demands of low-cost, flexible, and lightweight devices. From this subset of devices, graphene-based printable sensors are of specific interest due to their transparency, flexibility, biocompatibility, and high conductivity. In this research, a graphene-based ink is formulated and developed with the goal of having it exhibit characteristics that are suitable for a sensor, namely being electrically conductive, easily manufacturable, and printable through an inkjet-based printer. Based on the ink formulation methodologies presented in the journals Carbon and The Journal of Physical Chemistry Letters by Parvez et al. and Secor et al., respectively, a new graphene-based conductive ink formula and process was developed in this project. To develop this ink, a water-based graphene solution was prepared with a sonication process that demonstrated stable graphene suspension and dispersion in deionized water for up to one month. Additionally, the ink was characterized by a statistical sample of particle height and particle lateral size distributions; surface tension; density; viscosity as a function of shear rate; conductivity; and theoretical inkjet printability using a variety of scientific equipment and procedures. The final product was an ink that could be easily manufactured with simple lab equipment and exhibited a desirable set of liquid properties that represent the ability to be theoretically printed but failed to reach an experimental conductivity on the scale that was achieved in the Parvez et al. and Secor et al. studies.
The field of printable electronics and sensors has been experiencing increased interest and growth to meet the demands of low-cost, flexible, and lightweight devices. From this subset of devices, graphene-based printable electronics and sensors are of specific interest due to their transparency, flexibility, biocompatibility, and high conductivity. Among all modern ink printing technology, screen printing, spray coating, 3D printing, and inkjet printing are often utilized to fabricate flexible electronic applications from conductive ink. Compared with the other three, inkjet printing has received the most attention due to the simple printing process, high repeatability, economy, and time-savings compared to other printing techniques. However, inkjet printing often suffers from nozzle clogging due to aggregation of the particles in the conductive inks. In this research, a conductive graphene-based ink is developed to be used in a regular inkjet printer. A formulation process based on bath sonication and solvent exchange allows a graphene rich ink to be created with advantageous fluid properties that allow it to be printed easily.Small flake size of the graphene will allow us to avoid the issue of clogging the nozzle with flake aggregation and eventually aflexible hydration sensor will beprinted out with this graphene-based conductive ink.
“ … through the pyrolysis of L-glutamic acid Thomas Peters, Yijing Stehle Department of Mechanical Engineering SEM and … … ”
Abstract
An experimental study of Graphene quantum dots was conducted as a potential fluorescent, anti-bacterial additive for water-based paints using GQDs synthesized from L Glutamine. The L-Glutamine was polymerized to form light blue GQDs of low fluorescence intensity, which lost all fluorescence once added to the paint. The GQDs were tested for antibacterial properties against the growth of E.coli but failed to inhibit any growth. Raman and UV/vis spectroscopy were also conducted to determine functional groups as well as to determine peak light absorbance trends. While it was concluded that this method of GQD synthesis did not result in a promising additive for water-based paints, future research could continue the antibacterial testing by adding low concentrations of hydrogen peroxide as well as testing other facile methods of synthesis.
Ultra-thin, flexible, stretchable, and non-toxic sensors attract more and more attention as the need for more controlled non-invasive healthcare monitoring increases. Traditional conductive inks for electrode printing application require the use of metallic nanoparticles that can get very expensive to achieve high sensitivities. Graphene, a highly conductive, flexible, and high surface area material, has a much lower cost that makes it an ideal alternative. The rheological properties of the graphene ink developed allow it to be screen printed and inkjet printed, which allows it to be used in a wider range of applications. In this study, humidity sensors were drop cast with the as-prepared ink followed up with an annealing treatment. Annealing studies showed large increases in conductivity and sensing afterwards. The resulting electrochemical impedance spectra were further analyzed by fitting to an equivalent electrical circuit model showing that the electrode is behaving as predicted. Sensing data taken between high and low humidity environments show clear changes in impedance between them indicating that the electrode has the potential as a humidity sensing product and possibly as a sensor for other VOCs.
