Superhydrophobic and superoleophobic surfaces have so far been made by roughening a hydrophobic material. However, no surfaces were able to repel extremely-low-energy liquids such as fluorinated ...solvents, which completely wet even the most hydrophobic material. We show how roughness alone, if made of a specific doubly reentrant structure that enables very low liquid-solid contact fraction, can render the surface of any material superrepellent. Starting from a completely wettable material (silica), we micro- and nanostructure its surface to make it superomniphobic and bounce off all available liquids, including perfluorohexane. The same superomniphobicity is further confirmed with identical surfaces of a metal and a polymer. Free of any hydrophobic coating, the superomniphobic silica surface also withstands temperatures over 1000°C and resists biofouling.
The ability to manipulate droplets on a substrate using electric signals
-known as digital microfluidics-is used in optical
, biomedical
, thermal
and electronic
applications and has led to ...commercially available liquid lenses
and diagnostics kits
. Such electrical actuation is mainly achieved by electrowetting, with droplets attracted towards and spreading on a conductive substrate in response to an applied voltage. To ensure strong and practical actuation, the substrate is covered with a dielectric layer and a hydrophobic topcoat for electrowetting-on-dielectric (EWOD)
; this increases the actuation voltage (to about 100 volts) and can compromise reliability owing to dielectric breakdown
, electric charging
and biofouling
. Here we demonstrate droplet manipulation that uses electrical signals to induce the liquid to dewet, rather than wet, a hydrophilic conductive substrate without the need for added layers. In this electrodewetting mechanism, which is phenomenologically opposite to electrowetting, the liquid-substrate interaction is not controlled directly by electric field but instead by field-induced attachment and detachment of ionic surfactants to the substrate. We show that this actuation mechanism can perform all the basic fluidic operations of digital microfluidics using water on doped silicon wafers in air, with only ±2.5 volts of driving voltage, a few microamperes of current and about 0.015 times the critical micelle concentration of an ionic surfactant. The system can also handle common buffers and organic solvents, promising a simple and reliable microfluidic platform for a broad range of applications.
Flexible neural probes have been pursued previously to minimize the mechanical mismatch between soft neural tissues and implants and thereby improve long-term performance. However, difficulties with ...insertion of such probes deep into the brain severely restricts their utility. We describe a solution to this problem using gallium (Ga) in probe construction, taking advantage of the solid-to-liquid phase change of the metal at body temperature and probe shape deformation to provide temperature-dependent control of stiffness over 5 orders of magnitude. Probes in the stiff state were successfully inserted 2 cm-deep into agarose gel “brain phantoms” and into rat brains under cooled conditions where, upon Ga melting, they became ultra soft, flexible, and stretchable in all directions. The current 30 μm-thick probes incorporated multilayer, deformable microfluidic channels for chemical agent delivery, electrical interconnects through Ga wires, and high-performance electrochemical glutamate sensing. These PDMS-based microprobes of ultra-large tunable stiffness (ULTS) should serve as an attractive platform for multifunctional chronic neural implants.
•A flexible neural probe with an ultra-large tunable stiffness.•In vitro and in vivo electrochemical sensing of glutamate and chemical delivery.
A multifunctional chemical neural probe fabrication process exploiting PDMS thin-film transfer to incorporate a microfluidic channel onto a silicon-based microelectrode array (MEA) platform, and ...enzyme microstamping to provide multi-analyte detection is described. The Si/PDMS hybrid chemtrode, modified with a nano-based on-probe IrOx reference electrode, was validated in brain phantoms and in rat brain.
We have obtained interfacial properties of Galinstan, a nontoxic liquid-metal alloy, to help replace mercury in miniature devices. To prevent formation of an oxide skin that severely hinders the ...fluidic behavior of small Galinstan droplets and leads to inaccurate property data, we performed our experiments in a nitrogen-filled glove box. It was found that only if never exposed to oxygen levels above 1 part per million (ppm) would Galinstan droplets behave like a liquid. Two key properties were then investigated: contact angles and surface tension. Advancing and receding contact angles of Galinstan were measured from sessile droplets on various materials: for example, 146.8 and 121.5, respectively, on glass. Surface tension was measured by the pendant-drop method to be 534.6 10.7 mN/m. All the measurements were done in nitrogen at 28 with oxygen and moisture levels below 0.5 ppm. To help design droplet-based microfluidic devices, we tested the response of Galinstan to electrowetting-on-dielectric actuation.
Nanoscale zero-valent iron (NZVI) was successfully entrapped in chitosan (CS) beads for reduction of Cr (VI) from wastewater. The removal mechanism may include both physical adsorption of Cr (VI) on ...the surface or inside of CS-NZVI beads and subsequent reduction of Cr (VI) to Cr (III). The free amino groups and hydroxyl groups on CS may contribute little to hinder the formation of Fe(III)–Cr(III) precipitate. Entrapment of NZVI in CS beads prevents the particles from aggregation and oxidation. The results indicate that there is no significant difference between the reaction rates of bare NZVI and entrapped NZVI. Cr (VI) reduction kinetics follows a pseudo-first-order rate expression. The reduction capacity for Cr (VI) increases with increasing temperature and NZVI dosage but decreases with the increase in initial concentration of Cr (VI) and pH values. This study demonstrates that entrapment of NZVI in CS beads has the potential to become a promising technique for in situ groundwater remediation.
Based on Beijing’s Air Quality Index (AQI) and concentration changes of the six major pollutants from 2019 to 2021, the results are visualized through descriptive statistics, and the air pollution ...status and influencing factors of Beijing’s AQI are analyzed using the ARIMA model and neural network. A forecast system is built and the fitting effects of the two models are compared. The results show that PM2.5, PM10, and O3 of the six major pollutants have the greatest impact on AQI. Beijing’s air quality now shows a trend of improvement in recent years; however, there is obvious seasonal evidence that the summer pollution index has been high. Therefore, special attention should be paid to the treatment of ozone pollution in summer. Both models are useful for the forecast of AQI, but the forecast effect of the neural network model is better than that of the ARIMA model. Moreover, when using the additive seasonal model for the long-term forecast of monthly data, it is found that the Beijing AQI still shows seasonal cyclicality and has a slightly decreasing trend in the next two years. This research provides a basis for the forecast of air quality and policy enlightenment for environmental protection departments to deal with air pollution.
The difficulty of measuring very large contact angles (>150 degrees) has become more relevant with the increased popularity of super-repellent surfaces. Measurement is more difficult for dynamic ...contact angles, for which theoretical profiles do not fit well, and small capillary length liquids, whose sessile droplets sag by gravity. Here, we expand the issue to the limit by investigating dynamic contact angles of liquids with an extremely small capillary length (<1.0 mm), empowered by the superomniphobic surface that can super-repel even fluorinated solvents, which highly wet all materials. Numerically simulating and experimentally testing 13 different liquids on the superomniphobic surface, we discover their dynamic contact angles can be measured with a consistent accuracy despite their vastly different capillary lengths if one keeps the lens magnification inversely proportional to the capillary length. Verifying the droplet equator height is a key parameter, we propose a new Bond number defined by the equator height and optical resolution to represent the measurement accuracy of large contact angles. Despite negligible improvement for most liquids today, the proposed approach teaches how to measure very large contact angles with consistent accuracy when any of the liquids in consideration has a capillary length below 1.0 mm.
The number and field of researches on the application of Multi-Indicator Comprehensive Evaluation (MICE) are increasing. It is important to reflect on the understanding of the MICE method ...systematically and the issues implied behind it. This paper compares the core concepts and methodological elements of the three papers that systematically study the MICE method. It is found that the views of the three papers on the core issue are consistent and mutually supportive, but there are differences in the step division and sequence of the evaluation content. In addition, this paper considers the historical status of the MICE and holds that the key to solving the quality of weight lies in the "equivalent conversion" problem in the MICE. Taking the Human Development Index as an example, this paper illustrates the absoluteness of the "equivalent conversion" relationship. In addition, there are multiple processing methods for the MICE from the spatial dimension and multiple evaluation results accordingly, therefore, the results of the MICE need to be used carefully. Finally, based on the systematic summary and reflection of the MICE method, three suggestions are given for the application of the MICE method.
This study proposes a thermomechanical constitutive model for the shape memory effect of U–12.8 at.% Nb (U–Nb) alloy. The phenomenological model uses two variables for transformation. A transitional ...evolution function based on dissipative force is constructed, which removes the consistency condition. This improvement leads to a natural smoothness of all transitions, without any specifically defined hardening function. In addition, hysteresis is a natural result of the same reference force being converted forward and backward, and defining two different mixing energies is not necessary. The effect of strain rate is captured in the same frame by a function of the transition coefficient. This paper designs a robust and efficient numerical algorithm for the ordinary differential equation system. The model is validated by several special load cases. The simulation results are then compared with previous experimental data in the paper.
This study proposes a thermomechanical constitutive model for the shape memory effect of U–12.8 at.% Nb (U–Nb) alloy. The model here realizes a natural smoothness of all transitions and hysteresis for phase transformation. The model is validated by several special load cases. The simulation results are then compared with previous experimental data in the paper.
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