Production Characteristics of Large Soybean Oil Droplets by Microchannel Emulsification Using Asymmetric Through Holes

Large droplets with sizes of 50μm to 1000μm dispersed in another immiscible liquid are thermodynamically unstable. They are stabilized by emulsifier molecules dissolved in a continuous phase for a finite period of time. Liquid-liquid dispersions consisting of large droplets are usually used as templates for producing microparticles and microcapsules through gelation, polymerization, and other secondary reactions or processes in the food and pharmaceutical industries. In particular, monodisperse microparticles and microcapsules, which require uniform large droplets as templates, are useful microcarriers for micron-scale biological materials, having a high potential for controlled release of the bioactive substances yielded inside the micromaterials. To date, uniform large droplets have been applied to produce seamless microcapsules containing lactobacilli [1] and gel microbeads containing living cells [2]. In practice, a single nozzle set in a flow channel is used to produce uniform large droplets with sizes exceeding 200μm [1,3]. In this technique, a dispersed phase that has passed through a nozzle is injected into a coflowing continuous phase (Fig. 1a), and droplets are generated individually. This droplet generation process differs from conventional emulsification techniques in which larger droplets are broken up into non-uniform smaller ones by inhomogeneous extensional, shear, and/or cavitation forces [4]. Droplet generation mechanisms in a coflowing two-phase system may be divided into dripping driven by absolute instability and jetting driven by convective instability or absolute instability [3,5]. The size of the generated large droplets can be varied in a droplet production setup [3], indicating that their size is sensitive to the flow rates of both phases. It is also challenging to parallelize nozzles in a single setup. Vladisavljević and Williams recently reported that rotating-membrane emulsification is capable of producing uniform large droplets with sizes of 100μm by injecting a dispersed phase through a rotating cylindrical membrane with laser-drilled pores into a continuous-phase region (Fig. Production Characteristics of Large Soybean Oil Droplets by Microchannel Emulsification Using Asymmetric Through Holes