Capillary‐Based Microfluidics—Coflow, Flow‐Focusing, Electro‐Coflow, Drops, Jets, and Instabilities

Abstract

Capillary‐based microfluidics is a great technique to produce monodisperse and complex emulsions and particulate suspensions. In this review, the current understanding of drop and jet formation in capillary‐based microfluidic devices for two primary flow configurations, coflow and flow‐focusing is summarized. The experimental and theoretical description of fluid instabilities is discussed and conditions for controlled drop breakup in different modes of drop generation are provided. Current challenges in drop breakup with low interfacial tension systems and recent progress in overcoming drop size limitations using electro‐coflow are addressed. In each scenario, the physical mechanisms for drop breakup are revisited, and simple scaling arguments proposed in the literature are introduced.

Microfluidic formation of crystal-like structures

“…3 The size of the droplets as well as the droplet regime investigated (e.g., dripping or jetting regime) strongly depend upon the microfluidic geometry, the fluid properties, and the flow conditions. 3 A detailed description of the droplet formation mechanism falls outside the scope of this review; we refer the interested reader to the review by Nunes et al 3 or the more recent ones by Zhu et al 4 and Guerrero et al 5 3.1 Formation and stability of droplet crystals: hydrodynamic interactions among droplets…”

Microfluidics for core–shell drug carrier particles – a review

“…First, the device geometry is limited, and device fabrication's technicality can be complicated, making reproducibility of devices a problem. 25 Microuidics is an interdisciplinary science that can be used in many scientic elds, including the pharmaceutical industry, biomedical and chemical sensors, drug delivery, cell growth, and the food industry. 26 The main advantages of using microuidic systems are high efficiency, integration capability, mass production, reduced response time, and parallel operations.…”

“…149 A single emulsion is a droplet of one liquid dispersed in an immiscible uid that forms the continuous phase. 25 The common single emulsion includes oil-in-water (O/W) and waterin-oil (W/O) emulsions. 20 It is complicated to make core-shell droplets made of more than one immiscible liquid by other possible methods.…”

“…Flowfocusing particles are usually <1 mm, which is too small for long-term payload release applications. 25,145 6.1.3 Co-owing geometry. Two co-axially aligned uids move in the same direction in a co-ow system.…”

“…Naturally, alignment is accomplished by matching the outer diameter of the cylindrical capillary's circular cross-section and the inner side of the outer one's square cross-section. 25 6.1.4 T-junction geometry. The simplest and most used microuidic geometry is T-junction (Fig.…”