Photonic materials with positionally ordered structure can interact strongly with light to produce brilliant structural colors. Here, we found that the nonperiodic nematic liquid crystals of nanoplates can also display structural color with only significant orientational order. Owing to the loose stacking of the nematic nanodiscs, such colloidal dispersion is able to reflect a broad-spectrum wavelength, of which the reflection color can be further enhanced by adding carbon nanoparticles to reduce background scattering. Upon the addition of electrolytes, such vivid colors of nematic dispersion can be fine-tuned via electrostatic forces. Furthermore, we took advantage of the fluidity of the nematic structure to create a variety of colorful arts. It was expected that the concept of implanting nematic features in photonic structure of lyotropic nanoparticles may open opportunities for developing advanced photonic materials for display, sensing, and art applications.
Liquid metals (LMs) possess tremendous potential applications in flexible electronic devices, heat flow management, and smart actuators. Splitting the bulk LMs into microspheres is of great significance to fabricate free-standing and microscale LM-based functional materials and devices. However, it is difficult to disperse the bulk LMs into microspheres because of their large surface tension and high density. In this work, the capillary-based microfluidic chip is employed to continuously and automatically generate LM microspheres in a large scale. The capillary-based microfluidic fabrication is universally applicable in ionic aqueous solution, hydrophobic solution, and the polymeric aqueous solution. The precise size control of LM microspheres can be easily realized by the co-flowing configuration in the microchannels. The coefficient of size variation of monodispersed LM microspheres can be controlled to as low as 0.47%. The free-standing LM microspheres can be used as functional microelectrodes within a wide temperature range from −19.8 to 20 °C and to fabricate tunable integrated circuits with different output powers. Most importantly, the LM microspheres exhibit photothermal property, which is used to make the optical sensor with linear response and to conduct the solar energy harvesting. The capillary-based microfluidic fabrication of LM microspheres provides a facile and templated methodology for processing bulk LMs into microscale units. The LM microspheres with excellent electrical conductivity and photothermal property hold great promise for the development of miniature soft electronics, light-driven actuators, and energy conversion medium.
Some naturally flowing wells and some gas lift wells will experience flow instabilities characterized by regular or irregular cyclic variations in tubing pressure and flow rate. The unsteady equations of motion for flow out of the reservoir, flow out of the annulus and flow up the tubing are derived and then solved by the LaPlace Transform method. This analysis produces a characteristic equation whose coefficients allow one to determine if a particular well is stable or unstable. In addition, the characteristic equation coefficients can sometimes provide useful information on what well parameters can be changed to make an unstable well stable. Introduction Many oil wells, natural flowing or otherwise, reach a stage in their flowing life when liquid rates are low. Such wells may be candidates for flow instabilities, commonly called heading. Marshall defined heading as a flow regime characterized by regular and perhaps irregular cyclic changes in pressure at any point in the tubing string. Numerous studies of heading have been reported since the pioneering work of Donahue in 1930. Among them the first comprehensive discussion of the phenomenon of heading was the one given by Gilbert in his pioneering paper. Gilbert identified three types of heading: formation, tubing and annulus. Annulus heading, Gilbert explained, occurs when bubbles of free gas at the bottom of the hole are big enough to escape entrainment with the liquid entering the tubing (that is, big gas bubbles go up the annulus), and the gas liquid ratio in the tubing is smaller than the gas-lift optimum for the average producing rate of the well. This flowing condition occurs when there is no packer in the well. Tubing heading, whose effect Gilbert said is minimal, is due to the segregation of free gas from liquid in the rising fluid column in the tubing. He attributed the occurrence of formation heading to the case where a well is tapping a fissured or cavernous reservoir. Grupping etal analyzed formation heading and showed that it could be caused by two formations with different gas-liquid ratios producing together through one tubing string. Some of the first experimental field work was done by Fancher et al, and in that work, pressure traverses were recorded during a heading cycle. They found that there was no correlation between heading, flow rate, and gas-liquid ratio; however, in their particular experiment, no heading occurred when the liquid rate was above 192bpd. Ros and later Duns and Ros also mentioned the heading phenomenon as occurring in the transition zone between various flow patterns and prepared a correlation to predict pressure loss in this flow region. They found that heading was more severe in smaller pipes for lower liquid velocities. Zarrinal et al accumulated some data on the flow regime that exists just before a well heads up and dies. A recent work by Torre et al on annulus or casing heading concludes that heading only occurs when the slope of pressure loss as a function of gas flow rate is negative. On the particular case of heading in continuous-flow gas-lift wells, Simmons suggested the problem can be corrected by over-injection of gas. DeMoss et al offered an example in which gas-lift wells are stabilized by installing orifices in the lowermost gas-lift mandrel. P. 335^
Thermal comfort is of great significance to maintain people’s healthy state in physics, physiology, and psychology. Personal thermal management (PTM) that passively regulates the immediate environment around the human body has been proposed as a promising strategy to realize on-demand human thermal comfort. In this work, we propose a one-stop solution for the state of the art PTM by combining thermal shielding and thermal energy storage in a Janus-type wearable device, which is named a Janus-type hydroxyapatite-incorporated Kevlar aerogel@Kevlar aerogel supported phase-change material gel (HKA@KPG). The lower HKA with an ultralow thermal conductivity directly attached on the skin can effectively hinder heat transfer from the external environment to human skin. The upper KPG possessing a superior form stability and high energy storage capacity can absorb the heat generated by the human body to regulate the skin temperature. Both the HKA and KPG also demonstrate excellent biocompatibility. Due to its synergistic effect in thermal energy regulation, the Janus HKA@KPG has been applied in wearable PTM in static and dynamic modes to meet the thermal comfort requirements. It is anticipated that the one-stop thermal comfort solution for thermal shielding, thermal energy storage, self-supporting characteristics, wearability, and biosafety offers new possibilities for the next generation of wearable PTMs.
Dynamically engineering the interfacial interaction of nanoparticles has emerged as a new approach for bottom-up fabrication of smart systems to tailor molecular diffusion and controlled release. Janus zwitterionic nanoplates are reported that can be switched between a locked and unlocked state at interfaces upon changing surface charge, allowing manipulation of interfacial properties in a fast, flexible, and switchable manner. Combining experimental and modeling studies, an unambiguous correlation is established among the electrostatic energy, the interface geometry, and the interfacial jamming states. As a proof-of-concept, the well-controlled interfacial jamming of nanoplates enabled the switchable molecular diffusion through liquid-liquid interfaces, confirming the feasibility of using nanoparticle-based surfactants for advanced controlled release.
The state-of-the-art solar-thermal evaporators demonstrating high energy utilization efficiency, a high evaporation rate, and salt rejection are highly desirable in solar-driven low-energy water purification/harvesting. Herein, a novel Janus solar evaporator is constructed by loading polypyrrole (PPy) nanobelts on the polyvinyl alcohol (PVA) hydrogel. The PPy nanobelts present a high solar absorption of 98.3%, leading to a localized solar-thermal efficiency of 82.5% when insulated from bulk water by the PVA hydrogel. The porous PVA hydrogel and the hydrophilic PPy nanobelts enable the efficient three-dimensional water transport. Taking advantages of the synergistic effect in the water-energy nexus, the Janus PPy nanobelt@PVA hydrogel evaporator evaporates water with a high rate of 2.26 kg m −2 h −1 via 80.1% solar energy from 1 sun irradiance with a low PPy loading of ∼3 mg cm −2 even at a rate of 2.64 kg m −2 h −1 via 96.3% solar energy for a biomimetic conical evaporator. The Janus evaporator presents superior salt-resistant desalination and contaminant purification performance in seawater and sewage. Furthermore, a portable solar-thermal purifier equipped with the Janus evaporator desalts real seawater far above the drinking water standard with over a 99.9% salt rejection rate and eliminates 95.8% of chemical oxygen demand in real sewage, highlighting its potential for advanced clean water harvesting.
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