Ultrashort optical emission, with pulse duration ranging from nanoseconds to femtoseconds, is usually obtained from lasers. In this work, we achieve nanosecond-pulsed electroluminescence (EL) from a solution-processed fast-response quantum dot light-emitting diode (QLED). By modeling the QLED with a resistor-capacitor equivalent circuit and analyzing the transient current of the circuit, the dynamic of the carrier injection and transport process that fundamentally affects the transient EL of QLED is revealed, which helps to guide the optimization of fast-response QLED. Driven by a high current source, the optimized QLED can output stable and repeatable ultrashort EL with a pulse duration of 20 nanoseconds, a repetition rate of 50 kilohertz, and a high radiant exitance of 5.4 watts per square centimeter. Enabled by the nanosecond-pulsed EL, the developed QLED can be directly used as an instantaneous excitation source for time-resolved fluorescence spectroscopy. Meanwhile, its use as an exposure flash for high-speed imaging is also demonstrated.
Anand N. P. Radhakrishnan,Marco P. C. Marques,Matthew J. Davies,Brian O'Sullivan,Daniel G. Bracewell,Nicolas Szita
Flocculation is a key purification step in cell-based processes for the food and pharmaceutical industry where the removal of cells and cellular debris is aided by adding flocculating agents. However, finding the best suited flocculating agent and optimal conditions to achieve rapid and effective flocculation is a non-trivial task. In conventional analytical systems, turbulent mixing creates a dynamic equilibrium between floc growth and breakage, constraining the determination of floc formation rates. Furthermore, these systems typically rely on end-point measurements only. We have successfully developed for the first time a microfluidic system for the study of flocculation under well controlled conditions. In our microfluidic device (μFLOC), floc sizes and growth rates were monitored in real time using high-speed imaging and computational image analysis. The on-line and in situ detection allowed quantification of floc sizes and their growth kinetics. This eliminated the issues of sample handling, sample dispersion, and end-point measurements. We demonstrated the power of this approach by quantifying the growth rates of floc formation under forty different growth conditions by varying industrially relevant flocculating agents (pDADMAC, PEI, PEG), their concentration and dosage. Growth rates between 12.2 μm s−1 for a strongly cationic flocculant (pDADMAC) and 0.6 μm s−1 for a non-ionic flocculant (PEG) were observed, demonstrating the potential to rank flocculating conditions in a quantitative way. We have therefore created a screening tool to efficiently compare flocculating agents and rapidly find the best flocculating condition, which will significantly accelerate early bioprocess development.
Hang Yang,Junfeng Wang,Dongbao Wang,Daorui Wang,Jian Gao,Bin Li
The regulation of particle-laden droplet behavior is crucial for interfacial heat and mass transfer in the liquid-liquid reaction systems. Accordingly, a clear understanding of droplet dynamic behaviors is of crucial importance. In this study, the behaviors of solid-particle-laden droplets in an immiscible dielectric liquid are experimentally investigated under the effect of a non-uniform AC electric field by high-speed imaging. The evolution processes of droplet formation, coalescence, dispersion as well as liquid bridge are analyzed systematically in variable applied voltages and particle concentrations. Results show that the droplet formation process are accelerated by increasing particle concentration, producing smaller droplets. When the applied voltage exceeds a certain threshold, the charged droplet coalescence occurs while the presence of particles would reduce this critical voltage. Cascade coalescence happens in the pure system with increasing voltage while the particle-laden droplets tend to coalesce individually. The droplet dispersion is found to dominate at high electric field strengths with its oscillation angle increased by particle concentration. Additionally, the liquid bridge expansion is reduced by the addition of particles, hindering the droplet coalescence. These findings provide insights into the regulation of particle-laden droplet behavior under the effect of electric fields.
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