Oscillating sessile liquid marble - A tool to assess effective surface tension

A long-standing problem of liquid-marble based technology is the inconsistency of the effective surface tension values. This inconsistency could be due to particle size, particle type, volume of the liquid marble or the preparation method. The prevailing liquid marble preparation method is to roll a droplet on a powder bed. The lack of control of rolling duration or revolution speed could contribute to the inconsistent effective surface tension values. We hypothesize that a systematic preparation approach could improve the consistency of the effective surface tension values. In this work, we (i) determine the effective surface tension using the natural oscillation of a sessile liquid marble and (ii) investigate the effects of liquid marble preparation methods on the effective surface tension for the first time. We find that the effective surface tension values of a liquid marble prepared manually are inconsistent. In comparison, a systematic preparation method improves the consistency of the measured effective surface tension values. Interestingly, the systematic preparation at higher revolution speed causes interfacial jamming at the liquid marble shell which decreases the consistency. The results from this work can provide a deeper understanding of the fundamental characteristics of liquid marbles

Stretchable inertial microfluidics

The broad size distribution of biological particles requires redesigning and reoptimizing inertial microfluidic separation devices. The fixed separation range has been identified as the most pressing obstacle in the field of inertial microfluidics. The present work demonstrates the proof of concept of a novel stretchable microfluidic device that controls the length using a stretching platform. Changing the channel dimensions allows the device to be used for various particle sizes and flow rate ratios. We employed this approach for the separation of a mixture of particles. Stretching the device produce significant improvements in focusing and separation efficiency of the particles

Digital Imaging-based Colourimetry for Enzymatic Processes in Transparent Liquid Marbles

Liquid marbles are a promising microreactor platform that recently attracts significant research interest owing to their ability to accommodate a wide range of micro reactions. However, the use of destructive and ex-situ methods to monitor reactions impairs the potential of liquid-marble-based microreactors. This paper proposes a non-destructive, in situ, and cost-effective digital-imaging-based colourimetric monitoring method for transparent liquid marbles, using the enzymatic hydrolysis of starch as an illustrative example. The colourimetric reaction between starch and iodine produces a complex that exhibits a dark blue colour. We found that the absorbance of red channel of digital images showed a linear relationship with starch concentration with high sensitivity and repeatability. This digital-imaging-based colourimetric method was used to study the hydrolysis of starch by α-amylase. The results show high accuracy and applicability of first-order kinetics for this reaction. The demonstration of digital-imaging-based colourimetry indicates the potential of liquid marble-based microreactors

Dean-flow-coupled elasto-inertial three-dimensional particle focusing under viscoelastic flow in a straight channel with asymmetrical expansion-contraction cavity arrays

In this paper, 3D particle focusing in a straight channel with asymmetrical expansion-contraction cavity arrays (ECCA channel) is achieved by exploiting the dean-flow-coupled elasto-inertial effects. First, the mechanism of particle focusing in both Newtonian and non-Newtonian fluids was introduced. Then particle focusing was demonstrated experimentally in this channel with Newtonian and non- Newtonian fluids using three different sized particles (3.2 μm, 4.8 μm, and 13 μm), respectively. Also, the effects of dean flow (or secondary flow) induced by expansion- contraction cavity arrays were highlighted by comparing the particle distributions in a single straight rectangular channel with that in the ECCA channel. Finally, the influences of flow rates and distances from the inlet on focusing performance in the ECCA channel were studied. The results show that in the ECCA channel particles are focused on the cavity side in Newtonian fluid due to the synthesis effects of inertial and dean-drag force, whereas the particles are focused on the opposite cavity side in non-Newtonian fluid due to the addition of viscoelastic force. Compared with the focusing performance in Newtonian fluid, the particles are more easily and better focused in non-Newtonian fluid. Besides, the Dean flow in visco-elastic fluid in the ECCA channel improves the particle focusing performance compared with that in a straight channel. A further advantage is threedimensional (3D) particle focusing that in non-Newtonian fluid is realized according to the lateral side view of the channel while only two-dimensional (2D) particle focusing can be achieved in Newtonian fluid. Conclusively, this novel Dean-flowcoupled elasto-inertial microfluidic device could offer a continuous, sheathless, and high throughput (>10 000 s-1) 3D focusing performance, which may be valuable in various applications from high speed flow cytometry to cell counting, sorting, and analysis