Surfactant and oil formulations for monodisperse droplet emulsion PCR

A systematic survey of the oil and surfactant components of stable monodisperse w/o droplets suitable for various methods.

Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

Continuous flow real-time PCR device using multi-channel fluorescence excitation and detection

We have developed a ‘conveyor belt’ analog for real-time quantitative polymerase chain reaction (qPCR) in a continuous flow thermocycler. The device integrates droplet emulsion technology with LED and fiber optic fluorescence excitation in conjunction with a continuous flow thermal cycler to achieve real-time fluorescence detection.

Catalytic Effect of Nanoparticles on Primary and Secondary Phase Nucleation

Nanoparticles were shown to catalyze nucleation of primary and secondary phases in metal matrix nanocomposites (MMNCs). This catalysis is important as it contributes to the mechanical property enhancement in the MMNCs. Primary aluminium grain refinement was demonstrated in A356 matrix nanocomposites. Various types and sizes of nanoparticles (SiC, TiC, γ-Al2O3; 10-96 nm) were used to make these MMNCs and in all cases the MMNCs had smaller, more equiaxed grains compared to the reference A356. Using the droplet emulsion technique, undercoolings were shown to be significantly reduced. Undercoolings in the MMNCs were in good general agreement with the undercooling necessary for free growth, suggesting the applicability of this model to nucleation on nanoscale catalysts. Secondary phase nucleation catalysis was demonstrated in a zinc alloy AC43A MMNC and a binary Mg-4Zn MMNC. In AC43A, secondary phase nucleation was catalyzed with the addition of various nanoparticles (TiC, SiC, γ-Al2O3). The secondary phase nucleation catalysis in AC43A coincided with ductility enhancement. In Mg-4Zn, SiC nanoparticle addition changed the secondary phases that formed. MgZn2 was formed in the MMNC at relatively high temperatures consuming the Zn and reducing the amount of the low temperature Mg2Zn3 phase that formed in the reference alloy. The change in secondary phase formation coincided with significant enhancement in strength and ductility.

Generation and Control of Droplet in Cross Microchannel Flow With a Converging-Diverging Nozzle Shaped Section

This paper reports flow visualization experiments of droplet emulsions in the microfluidics that is composed of a flow-focusing (cross-junction) structure with a converging-diverging nozzle shaped section. The channel structure was made of polydimethylsiloxane (PDMS) with a channel of 73 μm in depth and 100 μm in width. Oil as the continuous phase and water as the dispersed phase were injected into the cross-junction inlets to form water-in-oil droplets. It is found that adding the converging-diverging section to the cross-junction significantly reduces the droplet size without largely increases the overall flow resistance and still achieve excellent uniformity (with coefficient of variation less than 3.5%). Throat of the converging-diverging section determines the breakup location of droplet emulsion. The size of droplets is controllable in a wide range (6–116μm) through the variation of throat width between 23 and 100 μm in conjunction with the flow rates of continuous and dispersed phases. This emulsion technique demonstrates that droplets with diameter as small as 10 μm or less can be produced in microchannels having dimensions on the order of 100 μm without use of surfactants.