Faster droplet production by delayed surfactant-addition in two-phase microfluidics to form thermo-sensitive microgels

Abstract

Microfluidic droplet templating produces monodisperse particles of well controllable sizes, but this is limited by the necessity to operate microfluidic devices at low flow rates in the dripping regime. Here, the per-channel rate of droplet production could be substantially increased by delayed surfactant addition as applied and verified for microfluidic production of N-isopropylacrylamide based microgels.

Two phase microfluidics with inviscid drops: Effects of total flow rate and delayed surfactant addition

“…Microfluidic devices with a flow focusing geometry as shown in Fig. 1 were built by soft lithography as an array of channels in a polydimethylsiloxane (PDMS) matrix bonded to a glass slide (for details, see [5]). The dimensions of PDMS-devices with two subsequent junctions were 40 x 40 µm 2 for the feeding channel, 40 x 40 µm 2 for the first collection channel after the first junction, and 80 x 40 µm 2 (width x height) after the second junction.…”

“…It was previously confirmed that the per-channel productivity of N-isopropylacrylamide (NIPAAm) droplets can be increased by delayed surfactant addition using a relatively expensive, low-viscosity fluorocarbon oil (HFE) as phase 2/3 [5]. It remains to be shown if this concept holds true also for other continuous phases such as paraffin oil that is better compatible with industrially concerns of production costs.…”

“…Besides some other strategies based e.g. on multiple channels operated at a time or multiplication of droplets by droplet-splitting [4], recently the concept of delayed surfactant addition was proposed [5]. This approach bases on maximizing the interfacial tension σ between phase 1 and 2 by omitting surfactants at the time of droplet formation.…”

“…Changing the phase 2 to a viscous oil, however, substantially affects the viscosity ratio λ12 = η1 · η2 -1 as a dimensionless parameter. In case of NIPAAm/HFE [5], λ12 ~ 1 and the drops are "viscous". In contrast, for a continuous phase of higher viscosity as should be used here, λ12 << 1 will result in "inviscid" drops with substantial alterations of the pressure distribution and pressure drop in the microfluidic channel [1].…”

Recent Advances in Applications of Droplet Microfluidics

“…Sarvothaman et al developed a strategy that involves using fluoroalkyl polyethylene glycol copolymers to reduce protein adhesion, which causes droplet movements to fail [17]. Seiffert et al proposed faster droplet production by delayed surfactant-addition to push droplet-based microfluidics to an industrially relevant scale [18]. Pirbodaghi et al developed an accurate approach that entails using bright-field microscopy with white light illumination and a standard high-speed camera for studying the fluid dynamics of rapid processes within microfluidic devices [19].…”