Frosting is a natural phase change phenomenon which happens frequently in nature and industry and has negative effects on a variety of applications. As a passive anti-frosting strategy, superhydrophobic surfaces have been paid more and more attention. To shed light on the process and space–time characteristics of frosting on superhydrophobic surfaces, the preparation methods of superhydrophobic surfaces were introduced first. Then, the internal mechanisms of anti-frosting for superhydrophobic surfaces were revealed from two perspectives of condensation frosting and defrosting. For the preparation of superhydrophobic surfaces, previous studies have shown that laser etching could obtain ideal surface parameters, but there is still a lack of a preparation scheme with low cost and good reliability. For the condensation frosting on superhydrophobic surfaces, the surface with regular surface morphology could realize the spontaneous wettability transformation of the droplets and maintain the size of the condensed droplets within 10–20 μm. The freezing time of droplets on the surface with a regular micro-nano structure is about 4.42 times longer than that on the surface without a regular micro-nano structure. The condensation stage and droplet freezing stage are the keys to preventing frost on superhydrophobic surfaces. For the defrosting on superhydrophobic surfaces, the photothermal defrosting method using metal nanowires, graphene, and carbon nanotubes has a broad application prospect. The results of this study summarized the achievements, problems, and challenges of the current research, so as to provide a reference for the anti-frosting technology of superhydrophobic surfaces in practical applications. 

Review on condensation frosting and defrosting experiments for superhydrophobic surfaces

3D superhydrophobic/superoleophilic sponge with hierarchical porous structure and robust stability for high-efficiency and continuous separation of oily wastewater

Three-dimensional separation materials with robust physical/chemical stability have great demand for effective and continuous separation of immiscible oil/water mixtures and water-in-oil emulsions, resulting from chemical leakages and discharge of industrial oily wastewaters. Herein, a superelastic polystyrene-based porous material with superhydrophobicity/superoleophilicity was designed and prepared by high internal phase emulsion polymerization to meet the aforementioned requirements. A flexible and hydrophobic aminopropyl terminated polydimethylsiloxane (NH2-PDMS-NH2) segment was introduced into the rigid styrene-divinylbenzene copolymer through 1, 4-conjugate addition reaction with trimethylolpropane triacrylate. The addition of NH2-PDMS-NH2 simultaneously improved the mechanical and hydrophobic properties of the porous material (the water contact angle from 141.2° to 152.2°). The material exhibited outstanding reversible compressibility (80% strain, even in liquid N2 environments) and superhydrophobic stability, even after being repeatedly compressed 100 times, water contact angle still remained above 150°. Meanwhile, the as-prepared material had outstanding hydrophobic stability in corrosive solutions (strong acidic, alkaline, high-salty, and even strong polar solvent), presence of mechanical interference, strong UV radiations, and high/low temperature environments. More importantly, the material could continuously and efficiently separate immiscible oil/water mixture and water-in-oil emulsions under the above conditions, showing huge potential for the large-scale remediation of complex oily wastewaters. 

Superhydrophobic/ superoleophilic polystyrene-based porous material with superelasticity for highly efficient and continuous oil/water separation in harsh environments

Due to ever-increasing environmental problems caused by oily wastewater, it is necessary to develop methods for separating oil/water mixtures. However, oil-in-water and water-in-oil emulsions are highly stable due to the action of surfactants, making them enormously difficult to separate. In this study, we report a 3D superhydrophobic/superoleophilic porous material with a microporous structure and strong negative charge via high internal phase emulsion polymerization to overcome these difficulties. The introduction of 10 wt% α-zirconium phosphate significantly improved the hydrophobicity of the material (water contact angle = 153°) and also endowed the material with a strong negative charge. The material could separate immiscible oil/water mixtures under turbulent condition and high- or low-temperature environments. Driven by gravity, the as-prepared monolith separated various oil/water mixtures with the separation efficiency exceeding 99.16%. Benefiting from the diametrically-opposing wettability and interconnected micropore structure, the foam could separate a Span 80-stabilized water-in-oil emulsion. Furthermore, a cationic surfactant-stabilized oil-in-water emulsion was also separated due to strong electrostatic interactions, which destabilized the oil/water interfacial film. Based on these properties, the as-prepared porous material shows huge potential for complex oily wastewater treatment. 

Fabrication of three‐dimensional porous superhydrophobic composites for immiscible and emulsified oil/water mixture separation

Three-dimensional superhydrophobic/superlipophilic porous materials have attracted widespread attention for use in the separation of oil/water mixtures. However, a simple strategy to prepare superhydrophobic porous materials capable of efficient and continuous separation of immiscible and emulsified oil/water mixtures has not yet been realized. Herein, a superhydrophobic graphene/polystyrene composite material with a micro-nanopore structure was prepared by a single-step reaction through high internal phase emulsion polymerization. Graphene was introduced into the polystyrene-based porous materials to not only enhance the flexibility of the matrix, but also increase the overall hydrophobicity of the composite materials. The resulting as-prepared monoliths had excellent mechanical properties, were superhydrophobic/superoleophilic (water/oil contact angles were 151° and 0°, respectively), and could be used to continuously separate immiscible oil/water mixtures with a separation efficiency that exceeded 99.6%. Due to the size-dependent filtration and the tortuous and lengthy micro-nano permeation paths, our foams were also able to separate surfactant-stabilized water-in-oil microemulsions. This work demonstrates a facile strategy for preparing superhydrophobic foams for the efficient and continuous separation of immiscible and emulsified oil/water mixtures, and the resulting materials have highly promising application potentials in large-scale oily wastewater treatment.

/pdf/facile-fabrication-of-superhydrophobic-graphene-polystyrene-mp06lddd.pdf

Facile Fabrication of Superhydrophobic Graphene/Polystyrene Foams for Efficient and Continuous Separation of Immiscible and Emulsified Oil/Water Mixtures

Superhydrophobic and magnetic PS/Fe3O4 sponge for remote oil removal under magnetic driven, continuous oil collection, and oil/water emulsion separation

This paper introduces a Combined symmetrical and complementary Input Pairs (CIP) of a Differential Difference Amplifier (DDA), to boost the total Common-Mode Rejection Ratio (CMRR) for multi-channel neural signal recording. The proposed CIP-DDA employs three input pairs (transconductors). The dc-coupled input neural signal connection, via the gate terminal of the first transconductor, yields a high input impedance. The high-pass corner frequency and dc quiescent operation point are stabilized by the second transconductor. The calibration path of differential-mode gain and Common-Mode Feedback (CMFB) is provided by the proposed third transconductor. The parallel connection has no need for extra voltage headroom of input and output. The proposed CIP-DDA is targeted at integrated circuit realization and designed in a 0.18-μm CMOS technology. The proposed CIP-DDAs with system CMFB achieve an average CMRR of 103 dB, and each channel consumes circa 3.6 μW power consumption.

A High CMRR Differential Difference Amplifier Employing Combined Input Pairs for Neural Signal Recordings.

This brief presents a differential difference amplifier (DDA) with a pseudo-differential (PD) common-mode feedback (CMFB) for neural signal recording. One of the input transconductors within the proposed DDA is connected to target neural signal, to ensure a high input impedance. Another input transconductor employs a self-stabilized topology to stabilize the dc quiescent point and to determine the cut-off frequency. The CMFB is applied via the proposed PD terminal. Benefiting from the parallel connection of PD, the common mode rejection ratio (CMRR) is approximately increased by a factor of differential-mode gain, without damaging the voltage headroom and dynamic range. Moreover, the proposed PD CMFB is suitable for multi-channel neural signal acquisition, the more the channels, the higher the CMRR. The circuits are targeted at IC realization, designed in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> CMOS technology. It achieves an input impedance of circa 51 <inline-formula> <tex-math notation="LaTeX">$\text{G}\boldsymbol{\Omega }$ </tex-math></inline-formula> at 100 Hz, a CMRR of 103 dB, and a power consumption of <inline-formula> <tex-math notation="LaTeX">$1.8~\boldsymbol {\mu }\text{W}$ </tex-math></inline-formula>. The proposed DDA (two channels) with a system PD CMFB consumes a die area of 0.24 mm2.

A Differential Difference Amplifier Employing Pseudo-Differential CMFB for Neural Signal Recording Applications

A Capacitively Coupled Chopper Instrumentation Amplifier with Deadtime Offset Reduction Technique for Neural Signal Sensing

In this brief, a bio-impedance (Bio-Z) based closed-loop control scheme is proposed for a wearable external diaphragm pacing (EDP) system. EDP delivers functional electrical stimulation to strengthen the muscle within the respiration system. Bio-Z sensor continuously and non-invasively measures the thoracic change to provide a linear relation of the respiratory rate and volume. The estimated slope of the Bio-Z variation generates and updates the needed stimulating parameters in real-time. The proposed EDP system yields a Bio-Z based feedback-controlled diaphragmatic stimulation, alongside with an improved degree of accuracy and robustness regarding to the open-loop controlled commercially available EDP devices. 

Bio-Z Based Feedback-Controlled External Diaphragm Pacing System

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