| Chemical synthesis,as one of the oldest scientific disciplines,plays a key role in promoting the advancement of human society.However,the intrinsic limitations of traditional batch synthesis methods have not been able to solve newly emerging problems.First,the poor selectivity of batch synthesis selectivity could not obtain controllable structure and properties,such as modifying molecules at specific sites or adjusting the layered structure of micro/nano materials.Second,their low level of integration and automation impede their applications in synthesis,screening and optimization.In addition,complex step-by-step operations,consumption of time,reagents and equipment,poor reproducibility and security issues could not implement the green and smart synthesis.The emergence of microfluidic technology has become an alternative approach to the synthesis of molecules and materials.Microfluidic synthesis has two major advantages:(1)fast heat and mass transfer in a geometry confined space;and(2)precise control to nanoliter and picoliter levels.These microreactors increase the efficiency,controllability and safety of synthesis and also extend the applicability in a variety of situations.Therefore,micro droplet was used as a reactor to synthesize magnetic nanoparticles.The main contents of this study are summarized as follows:1.A microfluidic device with double T-junctions was designed and fabricated for droplet generation and adjustment of droplet size.The chip was composed of double Tjunctions,a Y-junction and an S-channel.Two droplets were generated through Tjunctions,and they were met at the Y-junction and fused as a microreactor in the Schannel and then mixed automatically to generate magnetic NPs.By changing spin coating speeds(1000-3500 r/min)and the ratio of polymer precursor,crosslinker and silicone oil(10:1:1-10:1:6,w/w/w),the hydrophobicity of the surface of channel was investigated.The results showed that the spin coating speed was 2000 r/min and the ratio of polymer precursor,crosslinker and silicone oil was 10:1:5(w/w/w),the hydrophobicity of the surface of channel was the most hydrophobic.Besides,the process of droplet generation and fusion and the size variation of droplet were also studied by change the flow rate of the oil phase(300-700 μL/h)and the aqueous phase(20-500 μL/h).The results showed that keeping the flow rate of oil phase constant and increasing the flow rate of aqueous phase,the size of droplet increases.The size of droplet also increases with the decrease of oil phase while keeping the flow rate of aqueous phase constant.Therefore,the amount of reagent of the droplet can be adjusted by changing the flow rate.2.Magnetic nanoparticles were synthesized in microdroplets generated on chip.By changing the heating temperature(60 °C,65 °C,70 °C,75 °C,80 °C)and the flow rate ratio of the two aqueous phases(1:1,1:2,1:3,1:4,1:5),the morphology and size of the magnetic nanoparticles were investigated.The results showed that the size of magnetic nanoparticles increases with the increase of heating temperature.The maximum size of nanoparticles was 29 ± 4 nm,which synthesized at 80 °C,and the flow rates of oil phase,iron salt solution and ammonia water were 500 μL/h,60 μL/h and 20 μL/h.Besides,the magnetic properties of different magnetic nanoparticles were studied by measuring hysteresis loop,the saturation magnetization,coercivity.The hysteresis loop measured at room temperature showed that the magnetic nanoparticles have exhibited good magnetic properties.The coercivity is 5.2 Oe,and the saturation magnetization is 61 emu/g.On the other hand,the hysteresis loops were also measured at low temperature(100 K-250 K).It was found that the saturation magnetization and coercive force of the magnetic nanoparticles increased as the measured temperature decreased.For the nanoparticles synthesized at 80 °C,the saturation magnetization is 68.4 emu/g and the maximum coercivity is 48.5 Oe measured at 100 K. |
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