Air-conditioners have the highest energy consumption among the household appliances because of the improved thermal resistance by the filmwise condensation in summer and frosting in winter on the surface of hydrophilic foils of heat exchanger. The wet foils are also easy to adsorb dirts and reproduce bacteria, further affecting people health in the room. Here, through chemical oxidation and subsequent chemical modification, we fabricated superhydrophobic nano-arrays on the packed aluminum-foils and then assembled a novel air-conditioner heat exchanger using the foils. The foils showed high performance in self-cleaning, anti-condensation, anti-frosting, anti-corrosion and environment stability, promising a good candidate for improving energy efficiency of air-conditioners in future. The results of testing revealed that the cooling capacity and heat transfer coefficient from superhydrophobic heat exchanger increasing over 8 and 2 percent than conventional hydrophilic one under rated output working conditions. Moreover, the superhydrophobic exchanger under the condition of frosting has higher energy conversion (over 85%) than the conventional hydrophilic one after 60 min.

Manipulation of nano-liter droplets is a key step for many emerging technologies including ultra-compact microfluidics devices, 3D and flexible electronic printing. Despite progress, contamination-free generation and release of droplets by compact low-cost devices remains elusive. Here, inspired by the butterflies’ minute manipulation of fluids, we have engineered a superamphiphobic bionic proboscis (SAP) layout that surpasses synthetic and natural designs.¹ We demonstrate the scalable fabrication of SAPs with tunable inner diameters down to 50 µm by the rapid gas-phase nanotexturing² of the outer and inner surface of readily available hypodermic needles. Optimized SAPs achieve contamination-free manipulation of water and oil droplets down to a volume of 10 nl and a liquid surface tension of 26.56 mN/m in line good agreement our theoretical predictions³. The unique potential of this layout is showcased by the rapid and carefully controlled in-air synthesis of core-shell droplets with well-controlled composition. These findings provide a new low-cost tool for high-precision manipulation of nano-liter droplets, offering a powerful alternative to established thermal- and electrodynamic-based devices.

Figure 1 shows an exemplary superamphiphobic nanocoating patterned on an Australian coin and on a glass substrate. This is obtained by the deposition of nanoparticles aerosols generated either by low-temperature liquid or high temperature flame sprays. The resulting coatings can be made robust by the predisposition of a supporting micro-nanotextured layer of interpenetrated polymer networks.⁴

Figure 2a shows a schematic of the SAPs’ layout. Conformal coatings of re-entrant nanotextures are rapidly fabricated on the inner and outer walls of hypodermic needles by aerosol deposition of SiO₂ nanoparticles. This results in the self-assembly of an ultraporous (98%) nanoparticle network that is, thereafter, functionalized by atmospheric chemical vapour deposition of low surface energy fluoro-groups. The inner wall functionalization prevent in-needle adhesion, enabling superior control over droplet release and size, while resisting contamination by capillary rise (Figure 1b,c). The need to break capillary-bridges for droplet detachment is also prevented, further reducing the risk of contaminating the inner walls with liquid residues. The outer surface functionalization prevents contamination by creep during droplet generation and immersion in liquids. The performance of this design was initially demonstrated by the generation of a 400 nL oil (tetradecane) droplet with a SAP and a bare needle used as comparison. While the bare needle suffered from visible oil creep on its exteriors, the SAP preserved a pristine surface with no contamination (Figure 1b). Figure 3 demonstrate the facile contamination free generation and handling of core-shell nanodroplets by this SAP design.

REFERENCES:

[1] W. S. Wong, G. Liu and A. Tricoli, Superamphiphobic Bionic Proboscis for Contamination-Free Manipulation of Nano and Core-Shell Droplets. Small 2017, 10.1002/smll.201603688.

[2] G. Liu, W. S. Wong, N. Nasiri and A. Tricoli, Ultraporous superhydrophobic gas-permeable nano-layers by scalable solvent-free one-step self-assembly. Nanoscale 2016, 8 (11), 6085-6093.

[3] W. S. Y. Wong, G. Liu, N. Nasiri, C. Hao, Z. Wang and A. Tricoli, Omnidirectional Self-Assembly of Transparent Superoleophobic Nanotextures. ACS Nano 2017, 11 (1), 587-596.

[4] W. S. Wong, Z. H. Stachurski, D. R. Nisbet and A. Tricoli, Ultra-durable and transparent self-cleaning surfaces by large-scale self-assembly of hierarchical interpenetrated polymer networks. ACS applied materials & interfaces 2016, 8 (21), 13615-13623.

Droplet-based microfluidics system has become a new platform in the field of synthesis and analysis. The main research of microdroplets technology concentrates on the formation of micrometer-sized droplets and to manipulate them, including separation, consolidation, mixing, sorting, capture and assembly of droplets [1]. Many sorting methods have been reported, which typically include hydrodynamic sorting [1], electric field sorting [2], surface acoustic wave sorting [3] and micro valve sorting [4].

SAW is a kind of elastic sound wave which only propagates on the solid surface. Many articles have been reported to achieve micro droplets sorting using SAW technology [5]. However, there has been a concern in this technology. When the micro droplets flow through the SAW field, the SAW radiation force should only apply on the targeted liquid droplets but not on the adjacent droplets. As a result, the control of spacing between adjacent droplets is required so that only one droplet is in the SAW field at a time.

Flow focusing device was used to generate micro droplets. The continuous phase is fluorinated liquid FC-40 and the dispersed phase is deionized water. When they are focused on a cross structure, dispersed phase under the squeeze and shearing force of the continuous phase will break up to form droplets. Droplets are then poured into the flow channel, using the principle of fluid dynamics to control the spacing between droplets. Finally the droplets flow into the channel through the SAW field to achieve droplets sorting. The schematic drawing of SAW based micro fluidic sorting test setup is shown in Fig.1.

When the adjacent droplets flow through a steady fluid flow, there is a relationship between the distance change between adjacent droplets and the velocity change of droplets. Based on this, two kinds of flow channel are designed. One is the tapered flow channel, giving a change to the flow rate by changing the cross-sectional area. The other is a “T” shaped fluid channel. The volume flow rate of an inlet can be changed to control the flow rate of the droplets. The end of the flow channel is designed into two branches with different flow resistances for droplets sorting.

Fig.2 (a) shows the FEA simulation of the flow field of tapered flow channel design, in which the spacing between droplets is controlled by the flow velocity change induced by channel structure. Fig.2 (b) shows the flow field in the T shape channel, where the spacing between droplets is regulated by adjusting the flow rate of the two inlets. In the experiment, a high-speed video camera was used to measure the droplets velocity and droplet distance in different position. The injection flow rate is changed to obtain different spacing between droplets. As shown in Fig.3 and Fig.4, the results match well with the simulation analysis and the value of spacing ratio with and without regulation (X2/X1) has a linear relationship with the volume flow rate of the regulation fluid.

The driving force for the successful miniaturization of micro/ nanofludic systems in biotechnology and chemical industry is not only the reduction of sample volumes down to nano- and picoliter sizes but also leads to remarkably improved performance, such as higher separation efficiency, shorter analyzing times, and enhanced detection sensitivities.

The emerging experimental format makes possible a quantitative readout for large numbers of experiments with a precision comparable to the macroscopic scale. Chemotaxis, diagnostics, and biofilm are areas in which the first steps are being taken toward the long-term goal of transforming the way we design and carry out experiments.

In here, we will present this concept as microfludic device or microdroplets offering a great number of opportunities in chemical and biological research. They provide a compartment in which species or reactions can be isolated, they are monodisperse and therefore suitable for quantitative studies, they offer the possibility to work with extremely small volumes, single cells, or single molecules, and are suitable for high-throughput experiments

Print industry is one of the backbone industries in China, however, it produces huge amount of solid wastes, air emissions and wastewater. Based on the manufacturing of functional nanomaterials and controllable spreading and transferring of liquid droplets, they fabricated the superoleophilic patterns on the hierarchically structured superhydrophilic plate by ink-jet printing.^[1] Thus the image area and non-image area can be generated on the plate, which can be directly used as the printing-plate.^[2] It abandons the photosensitising process, and thus the new technology discharges no chemical pollutants, simplifies greatly the operation process, and lowered substantially the cost. Moreover, they employed the green printing technology in printed electronics based on metal nanoparticle ink,^[3] which simplifies the complicated preparation process of traditional photolithography method, and significantly prevents discharge of chemical pollutant. Nanomaterial green printing technology will lead the printing industry into a new age of greenization and digitalization.

This paper presents a high -throughput and -efficiency microfluidic Raman-activated droplet sorting (RADS) system combining many of the advantages of microtitre-plate screening. To validate the RADS system, the astaxanthin (AXT)-high-yield Haematococcus pluvialis (H. pluvialis) cells were sorted from the mixtures of cells, accumulating different amount of AXT.

Deposition pattern form the evaporative colloidal droplet has many applications in the scientific and industrial applications, since it provides a possible method to produce important nanoscale devices or develop the detection technology. Despite the preliminary application of the pattern-forming phenomena to concentrating chemicals, coating, printing, spraying, drying, painting, biomedical sampling, etc., achieving deep understanding of the dehydrating self-assembly in the application is still lacking. Particle assemblies can be found in drying the colloidal droplet. Controlling the particle organization and the final deposit patterns can be achievable from further understanding of droplet evaporative dynamics. The process to form the configuration in the drying droplet has been investigated theoretically and experimentally. In the experiments, the suspensions of colloidal droplet with the particle size at nano-scale particles in the deionized water were prepared with surfactant or without the surfactant. The surfactant acts the medium to modify the sticking parameter. The colloidal suspensions are carried out by well stirring first and then putting in an ultrasonication bath to ensure the even initial dispersion of the particles in the base fluid. The clean silicon wafer was used as a substrate for the colloidal sessile droplet drying. Right after the suspensions were prepared, we placed a tiny sessile droplet to dry while the drying patterns were directly recorded with the optical microscope. The interesting spreading and evaporation dynamics were found in the colloidal droplets. The formation of branched particle aggregation, coffee ring, uniform coverage and combined structures was observed during the droplet evaporation for pinning and depinning three phase line. To understand the controlled parameters, a simulation on the basis of Monte Carlo method is developed to explain the phenomena. The mathematical models respectively investigate the pinning and depinning behaviors to mimic a sessile colloidal droplet evaporation. The particle, liquid, vapor, and substrate interaction are considered. To understand the controlled parameters, we have developed the simple approaches: the two-dimensional (2D) Kinetic Monte Carlo (KMC) and Diffusion Limited Aggregation (DLA) models, to explain the various drying patterns from the colloidal droplets. We have used 2D KMC model to simulate the evaporation-induced fractal-like 2D structures found in drying the colloid droplets with the depinning three-phase line. The simulation shows a good consistency with the fractal structures observed in the experiments. Based on the nature of sticking between particles in the base fluids in a drying droplet, the diffusion limited cluster-cluster aggregation (DLCA) process by coupling with the biased random walk has been employed to investigate the particle aggregation. We have managed to simulate the experimentally observed transition from the uniform pattern to the coffee ring from the nanofluid droplets as a result of adding surfactant in the nanofluids. In addition, the 2D models have been translated into three-dimensional (3D) KMC and DLCA models. The advance of 3D models is discussed.

Droplets of nanoliter and subnanoliter are useful in a wide range of applications, particularly when their size is uniform and controllable. Examples include biochemistry, biomedical engineering, food industry, pharmaceuticals, and material sciences. One example of their many fundamental medical applications is the therapeutic delivery system for delivering site-specific therapy to targeted organs in the body and as the carriers for newer therapeutic options. The size, the size distribution, the generation rate and the effective manipulation of droplets at a scale of nano, pico, femto and even atto liters are critical in all these applications.  We make an overview of microfluidic droplet generation of either passive or active means and report a glass capillary microfluidic system for synthesizing precisely controlled monodisperse multiple emulsions and their applications in engineering materials, nanofluids, microfibers, embolic particles and colloidosome systems. Our review of passive approaches focuses on the characteristics and mechanisms of breakup modes of droplet generation occurring in microfluidic cross-flow, co-flow, flow-focusing, and step emulsification configurations. The review of active approaches covers the state-of-the-art techniques employing either external forces from electrical, magnetic and centrifugal fields or methods of modifying intrinsic properties of flows or fluids such as velocity, viscosity, interfacial tension, channel wettability, and fluid density, with a focus on their implementations and actuation mechanisms. Also included is the contrast among different approaches of either passive or active nature.

Spinning micro-pipette liquid emulsion generator for single cell whole genome amplification

Zitian Chen,^a,b Yusi Fu,^a,b Fangli Zhang,^a,b Lu Liu,^a,b Naiqing Zhang,^a Dong Zhou,^a Junrui Yang,^c Yuhong Pang,^a,b and Yanyi Huang*^,a,b,d

^a Biomedical Institute for Pioneering Investigations via Convergence (BIOPIC), School of Life Sciences, and College of Engineering, Peking University, Beijing, China

^b Beijing Advanced Innovation Center for Genomics (ICG), Peking University, Beijing, China

^c School of Electronics Engineering and Computer Science, Peking University, Beijing, China

^d Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China

* Corresponding author. E-mail: yanyi@pku.edu.cn

Many on-chip approaches that use flow-focusing^1-3 to pinch the continuous aqueous phase into droplets have become the most popular manner to provide monodisperse emulsion droplets. However, not every lab can easily adapt microfluidic workflow into their familiar protocols. Here we develop an off-chip approach, spinning micro-pipette liquid emulsion (SiMPLE), to generate highly stable monodisperse water-in-oil emulsion using a moving micropipette to disperse the aqueous phase in an oil-filled microcentrifuge tube. Compared with on chip approaches, this method provides a simpler way to produce picoliter-size droplets in situ with no dead volume during emulsification.

In the previous work, we demonstrated that through microfluidic chips monodisperse droplets-based eMDA can dramatically reduce the amplification bias while retaining the high accuracy of replication, which enables simultaneous identification of both small CNVs and high confidence SNVs from a single human cell⁴. The key point of this method is the high-quality of emulsion generation. With SiMPLE, the single-cell emulsion whole genome amplification was also performed to demonstrate that this novel method can seamlessly integrate with experimental operations and supplies that most researchers have been familiar with. Meanwhile, SiMPLE generator has effectively lower the technical difficulties in those applications relied on emulsion droplets.

A schematic view of the device design is illustrated in Figure 1. In the setup, a hydrophobic coated glass micropipette (inner diameter of the tip at the level of 10 µm) push the aqueous solution out to form monodisperse droplets while spinning. The droplets formation process is shown in Figure 2 with a few specific droplets indicated helping to understand. We performed emulsion whole genome amplification (eWGA) and analysed sequencing results of single mouse embryo stem cells (Figure 3), the distribution of the read coverage shows greatly improved evenness for the SiMPLE-eWGA approach.

Compared to other emulsion generation methods typically based on microfluidic approaches, this SiMPLE generator greatly simplifies the experimental set-up and operation procedure, and rules out sample loss or contamination during liquid transfer. In addition, the size of monodisperse picoliter droplets can be precisely regulated by the flow rate of the continuous phase and the motion velocity of the micropipette tip. With further improvements in the engineering of multiple micropipette platforms and integration with other biological assay chemistries, we believe this technique will become achievable in more emulsion-based reactions in biological and chemical research studies.

REFERENCES:

1.Seemann, R., Brinkmann, M., Pfohl, T. & Herminghaus, S. Droplet based microfluidics. Rep Prog Phys 75, 016601 (2012).

2.Anna, S. L., Bontoux, N. & Stone, H. A. Formation of dispersions using ‘flow focusing’ in microchannels. Applied Physics Letters 82, 364–366 (2003).

3.Whitesides, G. M. The origins and the future of microfluidics. Nature 442, 368–373 (2006).

4.Fu, Y. et al. Uniform and accurate single-cell sequencing based on emulsion whole-genome amplification. Proc. Natl.Acad. Sci. U.S.A. 112, 11923–11928 (2015)

A system-level prototype for EWOD driving was proposed and built, to aim the goal of droplet manipulation in 2D large scaled EWOD chip for biological detection.

When a 2D large scale EWOD chip is applied into application, there is still challenge in control of independent electrode for flexible applications. Droplet residues on electrode or any defects in the dielectrics would cause failures of droplet manipulation or detection accuracy. Therefore, effective control of electrodes, and discovery of the sites of the bugs and real-time routing for dodging of them are important for biological detections. We proposed a direct address and passive controlling method with N+M pins for M+N electrodes, and an electrical impedance-based sensing method for the bug finding. Lee algorithm was applied to automatically route droplet with real-time feedback of the bugs in the 2D EWOD chip with 10´10 electrode matrix. Hardware and software were developed applicable for 2D large scale EWOD chips.

Fig. 1 shows the schematic and picture of the system and the signal flow among the circuit components. Fig. 2 demonstrates the manipulation of multiple droplets simultaneously without conflict. Fig.3 gives the detection of the sites and sizes of the droplet residue larger than 40% of that of the electrode. Fig.4 expresses the real-time routing to dodging the bugs successfully.