Characterization of helium microplasma generated in a flow focusing microfluidic device

Abstract

Non-thermal microplasmas produced in a microchannel have several potential applications in analytical chemistry, environmental sensing, and surface modification of microfluidic chips for biomedical and lab-on-chip devices. This paper investigates the properties of an atmospheric pressure helium microplasma excited in a polydimethylsiloxane flow focusing microfluidic chip. The influence of input parameters such as applied voltage and gas flow rate on discharge characteristics is investigated in detail. Electron excitation and molecular rotational temperatures are determined with the Boltzmann plot technique. The rotational temperature from the N[Formula: see text] emission band was calculated in the range of 348–417 K. Electron density and temperature are determined using the well-known plasma diagnostic technique of Stark broadening. The emission lines of hydrogen Balmer (H[Formula: see text]) and neutral helium (501, 667, and 728 nm) are selected to measure the parameters of Stark broadening. The electron density and electron temperature were found to be in the range [Formula: see text]–[Formula: see text] cm[Formula: see text] and 10 800–12 493 K, respectively. The evaluated discharge parameters validate the non-thermal equilibrium state of the microplasma. The electrical diagnostics of plasma were performed by monitoring the signals of high voltage and current of the discharge. Moreover, the plasma modified surface (hydrophobic to hydrophilic) was verified by successfully utilizing the microchannel to form an oil-in-water micro-emulsion.