Study On Fabrication Of Phase Change Microcapsules Using Microfluidic Technology

Energy is one of the main factors influencing the development of human society. The application of phase change energy-storing technology helped to solve the incoherent energy supply in both time and space.In applying the phase change material,MEPCM can solve the disadvantages of the leak,the phase separation and the supercooling of PCM so that the usage of PCM will greatly expanded.However, these methods are disable in controlling the particle size, the different size and shape of MEPCM, the low coating rate and so on. Such problems not only bring troubles in MEPCM research, but also weaken the practical applications. In this article, we combines the mcrofluidics and MEPCMs together to solve these issues. First, according to the hydrophilic-hydrophobic property of the PCMS,we design a special microfluidic chip;then we separately study the droplet-generating mechanism of the three kinds of microfluidic devices (including PDMS chip, glass chip and three-way microfluidic device)and do research on how to control the size of the droplets; last, we managed to prepare MEPCMs by using PDMS chips and glass chips. By using video contact angle measuring instrument,optical microscopy,scanning electron microscopy, transmission electron microscopy,differential thermal scanning and so on, we summarize the basic principles and generating methods of the Phase change microcapsule and investigate the shapes and features of it.Chip’s design:We use soft lithography and compression moulding method to create a PDMS microfluidic chip depending on the surface characters of the liquid and materials; We use glass capillary tubes to adopted a simple glass microfluidic chip; We use a three-way which made by peek. These will be prepared to made the3-D device and applied in further study.The production and manifestations of the droplets:In order to study the emulsification process mechanism and control method of the microfluidic chips producing MEPCMS, we use the three chips on silicone and water emulsification,only to find that PDMS chip can well prepare W/O droplets;glass chip can easily prepare O/W droplets; the three-way chip can make both W/O and O/W droplets. By changing the flow rate of import liquid,we can prepare different size of micro-emulsion. The droplets made by microfluidic chips all have characteristics like uniform size, shape regular spherical, high controllable particle size and so on.The production and manifestations of the Phase change microcapsule:Using glass chip as the test platform, nonadecyl as the core material, polyurea as the shell material, we have made nonadecyl-polyurea MePCMs successfully. The average particle diameter is 200μm.MP is 31.6℃.Latent heat is 180J/G. The MEPCMS have a good spherical shape, and high cladding rate. The shell has good flexibility.The drape on the surface of the shell will be more stable during the melt and solidification of the PCM core. Using PDMS chip as the test platform, water as the core material, polyurea as the shell material, we have made water-polyurea MEPCMs successfully. The average particle size is 80μm. The water capsules can be stored in oil for a long time. However, the water capsules will slowly lose water when they are exposed to air. By using the SEM and TEM to study the shell, it has a sponge-like structure, some parts of which are not dense leading to the lose of water. We will polish the structure of the capsule shell in the subsequent experiments to improve its water-retention capacity.