Research Of A PDMS Pneumatic Pressure Driven Microvalve And Applications In Pneumatic Micro Mixing Chips

In recent years,pneumatic microfluidic chips have developed from simple operational unit to microfluidic large scale integration(m LSI),which are more and more successfully used in the biological and chemical analysis.Although the microfluidic systems themselves are very small in size,the necessary external devices are often bulky,non-portable,numerous,expensive,and difficult to be connected with chips because of hard property of their manufacturing materials.Therefore,it is necessary to propose a small and portable electromagnetic microvalve that can not only be used as an off-chip microvalve,but also be integrated with a complex polymer microfluidic system flexibly.Furthermore,the researches about dynamic response and flow rate characteristics of membrane microvalve controlled by an off-chip electromagnetic microvalve are still not perfect.In order to reduce the size of external devices and improve the accuracy of membrane microvalves,a polydimethylsiloxane(PDMS)pneumatic pressure driven microvalve is proposed in this paper.We present an off-chip electromagnetic microvalve,with a high-speed electromagnetic actuator and PDMS valve-body material.Two electromagnetic microvalves and an on-chip membrane microvalve constitute a PDMS pneumatic driven microvalve.The multiphysical coupling mathematical models of electromagnetic force,elastic deformation force of valve-membrane,flow force of gas in pneumatic microchannels,and flow force of liquid in liquid microchannels are developed to study dynamic response of spool displacement,dynamic flow rate,flow rate-duty cycle,flow rate-pressure characteristics of single electromagnetic microvalve,and flow rate,duty cycle-load pressure characteristics of the three-way microvalve.Correlations between flow rate of electromagnetic microvalves and duty cycle of actuated signals,spool displacement,and differential pressure of valve-port are investigated.Both the volume and pressure variations of the actuated chamber are simulated during inflation and deflation process.Deformation characteristics PDMS of the actuated membrane,dynamic response characteristics of pneumatic micro actuator are also studied.Correlation between liquid flow rate of the membrane microvalve and duty cycle of actuated signal,and pressure of the actuated chamber is analyzed.Based on fabrication craft of mold with microstructure and research on PDMS surface characteristics,encapsulation process of the proposed PDMS pneumatic pressure driven microvalve,involving dry-film-photoresist(DFP)mold fabrication,PDMS soft lithography process,air plasma treatment-different ratio of PDMS bonding method,is investigated.Several key properties of the PDMS pneumatic driven microvalve such as bonding strength of valve-body,fatigue of valve-membrane,spool force,dynamic displacement of spool,static and dynamic flow rate characteristics are tested experimentally,to validate the performance of the proposed PDMS pneumatic pressure driven microvalve,including size,pressure,flow rate,and response time.The deformation characteristics of the PDMS actuated membrane,pressure dynamic response characteristics of the actuated chamber and liquid flow rate characteristics of the membrane microvalve are experimented and analyzed.The liquid flow rate is modified according to the experimental results and the actions of membrane microvalve are recorded by a stereomicroscope in order to validate its operational reliability.According to the variable volume of the actuated chamber and the response characteristics of the electromagnetic microvalves,the control method of BangBang plus k plus PWM is developed to control the actuated chamber pressure.By using the Bang-Bang and k plus PWM control method,the step response time,pressure steady-state accuracy and pressure fluctuations are performed separately with different maximum and minimum thresholds,carrier frequencies and carrier amplitudes of PWM.Both advantages and disadvantages of two control methods are compared and analyzed.The effectiveness of the composite control method is validated by experimental results.A simple pneumatic micro mixing chip and high-temperature reflowing process of positive photoresist arc mold for liquid layer are presented.The encapsulation technology of three-layer pneumatic micro mixing chips is studied.Arc mold surface topography is tested by a surface profiler,and the effect of reflowing temperature,reflowing time,and microstructure width on the arc level of AZ50-XT positive photoresist mold is obtained.Mixing efficiency analysis method of two different dyes is developed by red-green-blue(RGB)color model,gray level transformation model,and variance equation.Pneumatic pressure and vibration frequency is controlled by the pneumatic microvalve.Mixing process of two different reagents using the proposed micro mixer is performed and recorded,and compared with free convective mixing process.The influence of actuated pressure and vibrating frequency on the mixing efficiency is studied.