مدل شبیه سازی و عملکردقطره ای تخلیه حرارتی حباب میکرواینژکتور

The present study investigates simulation model and droplet ejection performance of a thermal-bubble microejector. This model is achieved by coupling an electric-thermal model and flow model with bubble dynamics equations. We simulate the bubble nucleation and the bubble growth, to predict the droplet ejection process. The model is validated by comparing prediction results with experimental data. Especially, in forming one droplet, the results show that the ejection volume increases linearly with the thermal energy, and the variation range of the pulse width is within ∼0.2 μs. Moreover, the effects of the geometry of the nozzle, reservoir and thin-film resistance, applied current and pulse width on satellite droplets creation, droplet speed and volume are presented.

Depositing nanovolume of chemical or biochemical species with high precision and high reliability is today the major interest in various fields of applications. The functionalization of DNA chips is certainly the most challenging one. During the last 10 years, many studies have been devoted to the development of miniaturize systems enabling the ejection of small droplet but most of them suffer from a lack of flexibility due to the difficulty to integrate high density arrays of individually addressable ejectors. Thermal ejection is a good candidate to achieve simultaneously high density integration and individual actuation. This paper proposes a thermal ejection micro-array [1] enabling in situ oligonucleotide synthesis on DNA chips. It consists in a micro-array of individually addressable ejectors which eject nucleotides on a glass slide. The microejector is fabricated using monolithical silicon technologies. The microejector consists of three main elements, which are the supporting membrane, the resistance heater with the diode matrices for addressing and the SU8 nozzle. The working principle of the microejector is based on a thermal-bubble inkjet printing. A very short electric pulse is applied to a resistive heater to generate a high heat flux. If the surface temperature of the liquid is higher than the nucleation temperature, a vapor bubble is formed at the surface of the passivation layer. Sudden formation of the vapor bubble generates a pressure impulse, the rapid growth of the bubble expels a small liquid drop from the nozzle exit. After the applied current is removed, the temperature and pressure of the vapor decrease quickly, once the bubble collapses, the nozzle refills due to capillary forces for the next ejecting. The operating cycle of a thermal-bubble microejector is shown in Fig. 1. The operating cycle is divided into three phase: (1) the liquid is heated until bubble nucleation; (2) the bubble growth and collapse with droplet ejection; (3) refill of the reservoir.

The simulation model and droplet ejection performance of a thermal-bubble microejector are studied. Specially, this model is achieved by coupling an electric-thermal model and flow model with bubble dynamics equations. Simulation of the bubble nucleation and the bubble growth are solved to predict the droplet ejection process. The model is validated by comparing prediction results with experimental data. The variation range of the pulse width for forming a droplet is studied. Moreover, the effects of the geometry of the nozzle, reservoir and thin-film resistance, applied current and pulse width on satellite droplets creation, droplet speed and volume are presented. The typical working current and pulse width of the microejector are 10 mA, 28.9 μs, 14.5 mA, 10 μs, 20 mA, 5 μs and 24 mA, 3 μs, respectively. In forming one droplet, the results show that the ejection volume increases linearly with the thermal energy, and the variation range of the pulse width is within ∼0.2 μs. The droplet volume varies from 1 pL to 15 pL for the power consumption ranging from 45 mW to 0.5 W. This model can be used to understand how the microejector works and to facilitate the operation of the microejector. It can also optimize the design and droplet ejection performance of the microejector.