Development of synchronization for multi-microchannel and high-throughput “Air-Bubble Coating” system

With the growing demand for the rapid changes of consumer electronics, a variety of coating methods have been applied in high-tech industries. Among these coating techniques, pattern coating technology has gradually become the mainstream due to its eco-friendly features. Air-Bubble Coating is a novel mask-less pattern coating method, and it generates discontinuous patterns by continuously coating the segmented gas-liquid micro-two-phase flow onto the substrate. It has superior characteristics such as simple operation, wide viscosity applicable range, and good compatibility to roll-to-roll process. This research aims to grow Air-Bubble Coating into an industrial mass production technique. According to the required key technologies, the structure of this dissertation work is divided into three major parts: I. The development of real-time size control system for gas-liquid micro-two-phase flow: First of all, the effect of fluid driven sources on the size uniformity of gas-liquid micro-two-phase flow has been investigated. The commonly used syringe pump would produce about ±20% bubble/droplet size variation while the constant pressure source could generate uniform size of bubbles/droplets with the coefficient of variation less than 0.73%. Second, the operational range of slug flow, which is essential for Air-Bubble Coating, can be well-predicted based on the equivalent single-phase flow model, and the channel geometric factor G* has been identified as the key parameter that affects the scope of slug flow region. Finally, a closed-loop system for controlling the size of gas-liquid micro-two-phase flow in real-time has been developed. The bubble/droplet size variable range of this system reaches one order of magnitude, and the overall size control error is less than ±3%. II. The development of on-line detection system for gas-liquid micro-two-phase flow: An electrical resistance sensing system and an optical microfiber sensing system have been developed to on-line detect the gas-liquid micro-two-phase flow. For electrical resistance detection system, the conductivity difference of liquid and gas was applied to identify the gas-liquid interface, and the velocity and size measurement errors were within ±1% and ±6%, respectively. However, in order to operate properly, the continuous phase fluid must be conductive. In contrast, the microfiber detection system obtains the information of gas-liquid interface based on the refractive index change of the working fluid. With only tiny sample volume (100 nL), the on-line detection of refractive index, velocity, and size can be performed simultaneously. The measurement resolution for refractive index, velocity, and size are 2 × 10-4, 50 μm/s and 5 μm, respectively. This optical sensing system is robust enough for the precision positioning of Air-Bubble Coating. III. The development of synchronization for the generation and coating of multi-channel gas-liquid micro-two-phase flow: Three microfluidic structures for passively maintaining the synchronicity of gas-liquid micro-two-phase flow generation with common fluid sources have been developed. The first microfluidic structure combines the design of T-junction and ladder channels, and it utilizes fluid coupling to generate out-of-phase gas-liquid micro-two-phase flow in two parallel channels. The phase lag between these two channels gradually approaches zero as the bubbles/droplets flow downstream. However, it is difficult to apply this design to more than two parallel channels. The second microfluidic structure is two capillary valves with dual diffusor. It can produce in-phase gas-liquid micro-two-phase flow in two parallel channels, but the working frequency is much lower than the first design. The third one is a three parallel flow-focusing device with downstream ladder channels. It can generate in-phase gas-liquid micro-two-phase flow between all channels with high frequency, and it is suitable to scale up to multi-channel applications. For the multi-channel coating of gas-liquid micro-two-phase flow, a simple technique has been developed to control the uniformity of flow distribution within parallel channels based on Hagen-Poiseuille''s law, and the diversion error is less than ±1%. Furthermore, the operational range for three channel synchronization coating has been investigated. The phase difference between each channel can be controlled within ±4.6º. As for ten parallel channels coating, the phase difference of gas-liquid micro-two-phase flow among all channels was less than ±7.5º.