AC electrokinetics has shown great potential for microfluidic functions such as pumping, mixing and concentrating particles. So far, electrokinetics are typically applied on fluids that are not too conductive (<0.02 S/m), which excludes most biofluidic applications. To solve this problem, this paper seeks to apply AC electrothermal (ACET) effect to manipulate conductive fluids and particles within. ACET generates temperature gradients in the fluids, and consequently induces space charges that move in electric fields and produce microflows. This paper reports two new ACET devices, a parallel plate particle trap and an asymmetric electrode micropump. Preliminary experiments were performed on fluids with conductivity at 0.224 S/m. Particle trapping and micropumping were demonstrated at low voltages, reaching approximately 100 microm/s for no more than 8 Vrms at 200 kHz. The fluid velocity was found to depend on the applied voltage as V(4), and the maxima were observed to be approximately 20 microm above the electrodes.
Perovskite solar cells (PSCs) are an emerging photovoltaic technology that promises to offer facile and efficient solar power generation to meet future energy needs. PSCs have received considerable attention in recent years, have attained power conversion efficiencies (PCEs) over 22%, and are a promising candidate to potentially replace the current photovoltaic technology. The emergence of PSCs has revolutionized photovoltaic research and development because of their high efficiencies, inherent flexibility, the diversity of materials/synthetic methods that can be employed to manufacture them, and the various possible device architectures. Further optimization of material compositions and device architectures will help further improve efficiency and device stability. Moreover, the search for new functional materials will allow for mitigation of the existing limitations of PSCs. This review covers the recently developed advanced techniques and research trends related to this emerging photovoltaic technology, with a focus on the diversity of functional materials used for the various layers of PSC devices, novel PSC architectures, methods that increase overall cell efficiency, and substrates that allow for enhanced device flexibility.
Pumping of fluids with precise control is one of the key components in a microfluidic device. The electric field has been used as one of the most popular and efficient nonmechanical pumping mechanism to transport fluids in microchannels from the very early stage of microfluidic technology development. This review presents fundamental physics and theories of the different microscale phenomena that arise due to the application of an electric field in fluids, which can be applied for pumping of fluids in microdevices. Specific mechanisms considered in this report are electroosmosis, AC electroosmosis, AC electrothermal, induced charge electroosmosis, traveling wave dielectrophoresis, and liquid dielectrophoresis. Each phenomenon is discussed systematically with theoretical rigor and role of relevant key parameters are identified for pumping in microdevices. We specifically discussed the electric field driven body force term for each phenomenon using generalized Maxwell stress tensor as well as simplified effective dipole moment based method. Both experimental and theoretical works by several researchers are highlighted in this article for each electric field driven pumping mechanism. The detailed understanding of these phenomena and relevant key parameters are critical for better utilization, modulation, and selection of appropriate phenomenon for efficient pumping in a specific microfluidic application.
ABSTRACT:In this report, we have tried to reveal that there is much conceptual commonality between the two fundamental theoretical descriptors of chemistry and physics-the electronegativity and the hardness. The physical hardness was introduced and theorized by condensed matter physicists. The chemical hardness was introduced by chemists to generalize and rationalize the HSAB principle. We have tried to establish that the physical hardness and the chemical hardness with evolution of time have converged to one and the same general principle-the hardness. We have also tried to understand the physical basis and operational significance of another very important descriptor arising out of theoretical constructs of chemistry-the electronegativity. We have relied upon the fact that, since these descriptors are not observables, there is no possibility of their quantum mechanical evaluation. These descriptors, therefore, should be and must be reified before suggesting ansatz for their evaluation. We have dwelt at length upon the effort of density functional definition and evaluation of electronegativity and hardness and discovered the inherent inner contradiction of the theory and measurement. We have also noted that a good number of scientists hold the opinion that the density functional formula of electronegativity is ϭ I and that of hardness is ϭ I, where I is the ionization potential of the chemical system. This study concludes that the two fundamental descriptors-the hardness and the electronegativity originate from the same source-the electron attracting power of the screened nucleus upon valence electrons and discovers the surprising result that if one measures hardness, the electronegativity is simultaneously measured and vice versa. We have also explored the ansatz of semiempirical evaluation of electronegativity and hardness of atomic systems involving the radius of the atoms. We have noted that the ansatz for electronegativity and hardness is the same. To justify our statement that if one measures hardness, the electronegativity is simultaneously measured and vice versa, we have used the evaluated set of hardness for 103 elements of the periodic table as a scale of electronegativity and found that such set of hardness data satisfies the sine qua non of a satisfactory scale of electronegativity. The electronegativity and the hardness are two different appearances of the one and the same fundamental property of atoms. They are different and also nondifferent. They are different in their fields of application. They are nondifferent when we discuss the basic philosophical structures of their origin and development.
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