ANALYTICAL MICROSYSTEMS Exercise No. 2 Glass microchip for droplet chemistry Goals of exercise: During this laboratory students will investigate range of ratio of water and oil pressure which is necessary to achieve droplets generation. Afterwards students will measure generation frequency f produced droplets. Microfluidic system for droplet generation and management has been developed at the Division of Microengineering and Photovoltaics at the Faculty of Microsystem Electronics and Photonics as a master s thesis. Laboratory set-up: NOTICE: Laboratory set-up is equipped with very precise and sensitive elements. The total value of the laboratory set-up is estimated at 2000 EUR. 1) precision reducer with manometer to control the WATER flow, 2) precision reducer with manometer to control the OIL flow, 3) precision reducer with manometer to control the DETERGENT flow, 4) pneumatic throttle, 5) pneumatic throttle, 6) pneumatic throttle, 7) tank of WATER blue color, 8) tank of OIL red color, 9) tank of detergent, 10) waste container, 11) four microfluidic valves, 12) microfluidic tee, 13) microfluidic X-pieces, 14) microfluidic chip, 15) microscope Bresser, 16) computer.
main valve Fig. 1. Schematic construction of laboratory set-up Microfluidic chip: The microfluidic chip is made of borosilicate glass (Borofloat 33, Schott, Deutchland), 25 mm 50 mm 2.2 mm. The cross-channel configuration 300 µm 50 µm with the T shape for droplet generation and a circular channel extension for combining of nanodrops (Fig. 2). Wet etching the pattern in the glass substrate was performed using a solution of 40% HF: 35% HCl and chemically resistant mask film. Inlet holes of 1 mm diameter has been drilled in the second glass substrate. Structures have been subjected to the cleaning (detergent, acetone, isopropanol, Piranha (3:1), washing with deionized water), after that permanently connected by high-temperature fusion bonding. Fig. 2 Schematic design of microfluidic channels in the chip
The laboratory flow: NOTICE: Practical laboratory classes can start ONLY with the permission of the teacher. Please follow the points precisely. Preparation for measurements: 1. switch on the computer, 2. create a folder called of your index number, 3. run a program for recording video CamApp (push button picture on the handy microscope), 4. turn the objective on the handy microscope to change zoom, 5. push button mode on the handy microscope to change the type of lighting, 6. to change the brightness use two buttons on the handy microscope, 7. push button picture on the handy microscope to take a picture. Program CamApp instruction: 1. specify the path for saving the video (File Set capture file Folder), 2. adjust video settings (Option Video Capture Filter), 3. to set time of video: Capture Record time limit, 4. to begin the process of recording movie: Capture Start Capture, 5. to end the process of recording movie: Capture Stop Capture. Measurement start up: 1. make sure that the pressure regulators are in the closed position, 2. open the main valve pressure, 3. make sure that the valves 1 and 2 are open and valves 3 and 4 are closed, 4. turn on water and oil regulators and set value 40 kpa on each, 5. wait until you see oil (red) and water (blue) in the channel of the chip cover, 6. as soon as water and oil show up, adjust value of pressure in the way that 7. water and oil enter chip microchannels to achieve laminar flow (do not exceed 60 kpa for each), 8. adjust microscope and video settings to achieve the best picture quality.
The range of ratio of water and oil pressure measurement: 1. choose the pressure of water and oil to obtain droplets generation (do not exceed 60 kpa for each), 2. when you obtain droplets generation, begin the process of recording movie (The film should take 1 minute), 3. change the pressure of water with constant oil pressure, 4. for each pressure change record 1 minute video, 5. fill Table 1 which is in remarks, 6. change the pressure of oil with constant water pressure, 7. for each pressure change record 1 minute video, 8. fill Table 2 which is in remarks. Cleaning of the microfluidic chip: 1. make sure that the pressure regulators are in the closed position, 2. set the valves 1 and 2 in the closed position, and valves 3 and 4 in the open position, 3. set the controller detergent at 30 kpa, 4. the chip must be cleaned with a detergent - cleaning time is 25 minutes, 5. after cleaning set detergent reductor in the closed position, 6. set valves 1, 2, 3 and 4 in the closed position, 7. close the main valve supplying compressed air to the position. Study results: - define ratio of water (W) and oil (O) when the oil pressure is constant - fill table 1, - define ratio of water (W) and oil (O) when the water pressure is constant - fill table 2, - define frequency of droplet generation per minute, - add graphs in the report - droplet generation frequency as a function of water pressure and droplet generation frequency as a function of oil pressure. Remarks: The frequency of droplet generation can be determined by analyzing the recorded video in the selected section of the channel.
Oil pressure = Table 1. Range of water and oil pressure and generation frequency f droplets for oil pressure = const No. Water [kpa] Ratio of W and O f [droplets per minute] 1 2 iv + 4 3 iv + 2 4 The initial value (iv) 5 iv - 2 6 iv - 4 Water pressure = Table 2. Range of water and oil pressure and generation frequency f droplets for water pressure = const No. Oil [kpa] Ratio of W and O f [droplets per minute] 1 2 iv + 4 3 iv + 2 4 The initial value (iv) 5 iv - 2 6 iv - 4 Issues to prepare individually: 1. Definition of Droplet Based Microfluidics. 2. What is the volume of the droplets in standard Droplet Based Microfluidics? 3. What kinds of liquids are used in Droplet Based Microfluidics?