Lee Doojin, Beesabathuni Shilpa N, Shen Amy Q
Micro/Bio/Nanofluidics Unit, Okinawa Institute of Science and Technology Graduate University , Okinawa, 904-0495 Japan.
Mechanical Engineering Department, University of Washington , Seattle, Washington 98195, USA.
Biomicrofluidics. 2015 Dec 15;9(6):064114. doi: 10.1063/1.4937897. eCollection 2015 Nov.
Spherical and non-spherical wax microparticles are generated by employing a facile two-step droplet microfluidic process which consists of the formation of molten wax microdroplets in a flow-focusing microchannel and their subsequent off-chip crystallization and deformation via microdroplet impingement on an immiscible liquid interface. Key parameters on the formation of molten wax microdroplets in a microfluidic channel are the viscosity of the molten wax and the interfacial tension between the dispersed and continuous fluids. A cursory phase diagram of wax morphology transition is depicted depending on the Capillary number and the Stefan number during the impact process. A combination of numerical simulation and analytical modeling is carried out to understand the physics underlying the deformation and crystallization process of the molten wax. The deformation of wax microdroplets is dominated by the viscous and thermal effects rather than the gravitational and buoyancy effects. Non-isothermal crystallization kinetics of the wax illustrates the time dependent thermal effects on the droplet deformation and crystallization. The work presented here will benefit those interested in the design and production criteria of soft non-spherical particles (i.e., alginate gels, wax, and polymer particles) with the aid of time and temperature mediated solidification and off-chip crosslinking.
通过采用一种简便的两步液滴微流控工艺来生成球形和非球形蜡微颗粒，该工艺包括在流动聚焦微通道中形成熔融蜡微滴，以及随后通过微滴撞击不混溶液体界面在芯片外进行结晶和变形。在微流控通道中形成熔融蜡微滴的关键参数是熔融蜡的粘度以及分散相和连续相流体之间的界面张力。根据撞击过程中的毛细管数和斯蒂芬数，描绘了蜡形态转变的粗略相图。进行了数值模拟和解析建模相结合的研究，以了解熔融蜡变形和结晶过程背后的物理原理。蜡微滴的变形主要由粘性和热效应主导，而非重力和浮力效应。蜡的非等温结晶动力学说明了时间相关的热效应如何影响液滴的变形和结晶。本文所展示的工作将有助于那些借助时间和温度介导的凝固及芯片外交联来设计和生产软质非球形颗粒（如藻酸盐凝胶、蜡和聚合物颗粒）的研究人员。
