Nanoscale Electrowetting Effects Studied by Atomic Force Microscopy

Electric field effect on adhesive characteristics of the polymethyl methacrylate (PMMA) surface is studied by using force spectroscopy method of atomic force microscope (AFM). The adhesive interaction between the AFM tip and dielectric surface is obtained by monitoring the force−distance spectroscopy, which reflects the change of the surface tension under the influence of external electric field. Such changes in adhesion characteristics are attributed to the electrowetting effect at relatively low electrical field strength and the electrowetting saturation effect at high electrical field strength. It is also suggested that the force spectroscopy method has noticeably high stability in studying adhesion characteristics at nanometer scale

Ultrathin Flexible Graphene Film for High-Performance Electromagnetic Interference Shielding via Infrared-Assisted Rapid Thermal Shock Exfoliation

Lightweight, flexible, and high-strength electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are desirable for portable/wearable electronics. Here, we reported an efficient synthesis of a highly aligned conductive graphene film by an infrared-assisted rapid thermal shock exfoliation. Benefiting from its noncontact thermal radiation heating with a homogeneous and efficient thermal field, gas is rapidly generated from graphene oxide films. This results in a sharp increase in the interlayer pressure and thus forms a mesoporous interlayer structure, which could be compressed into compact films with enhanced conductivity and mechanical strength. A relatively low-temperature treatment at 1500 °C healed partial defects in graphene sheets and gave an ultrathin (∼10 μm) graphene film with remarkable properties of high electrical conductivity of ∼1500 S cm–1, a high EMI SE of 52 dB in the X band, and high tensile strength of up to 160 MPa. This time-saving fabrication process makes graphene film a competitive candidate for practical EMI shielding applications

Quantifying Surface Charge Density by Using an Electric Force Microscope with a Referential Structure

A comparative method was proposed to quantitatively measure the charge density on sample surfaces at the nanometer scale by using an electric force microscope (EFM). By introducing a millimeter-sized conductive sphere as a charge reference, whose surface charge density was proportional to the applied voltage, the electrostatic interaction between an EFM probe and the sphere could be calibrated as a function of charge density. Because the Coulombic force acting on the probe is proportional to the linear term of the phase shift (Δθ) versus tip voltage (Vt) characteristics, the charge density of an unknown sample could be derived by comparing the slopes of the characteristic curves measured on the studied sample with that obtained on the reference sphere whose absolute charge density had been known. The approach was applied to determine the charge density of a freshly cleaved mica surface. The comparative scheme avoids the complex influence from the irregular shape of EFM tips, providing a facile approach for quantitative analysis of the charge density on sample surfaces at the nanometer scale

Wettability-Patterned Meshes for Efficient Fog Collection Enabled by Polymer-Assisted Laser Sintering

Water collection from fog has been considered as a meaningful strategy to alleviate the scarcity of fresh water in some arid and semi-arid lands. Due to the specific wettability pattern on the back, Stenocara beetles show amazing capability for water capture from fog. Various biomimetic flat surfaces with wettability have been reported in the last decade. However, it is still a great challenge to accurately construct a patterned surface on a mesh, which is the common material in the practical application of fog collection. Herein, a facile and easy-to-operate strategy for surface modification on a stainless-steel (SS) mesh based on polymer-assisted laser sintering has been developed. A certain polymer film can be chosen to obtain different wettabilities because of the elemental composition and microstructure after laser sintering. Laser sintering following pre-design contributed to accurate control of the pattern geometry, size, and site. A bio-inspired pattern mesh with isolated triangular superhydrophobic regions and hydrophilic channels was fabricated for water collection from fog flow. Due to the good balance of water droplet capture, growth, and removal, the rationally designed SS mesh showed a satisfactory collection rate as high as 177.65 mg cm–2 h–1, which was a nearly 16-fold increase compared to that of the pristine SS mesh. The obtained mesh also showed high stability not only in long-term applications but also in several cycles of regeneration. Based on the outstanding performance of fog water collection, the patterned SS mesh could be of great value in practical applications. Furthermore, the polymer-assisted laser sintering strategy for surface modification on mesh could potentially be applied in various fields for high efficiency and scalability

Preparation of Insoluble Bis(2-bromoacetyl)biphenyl via a Photoultrasound Enhanced Continuous Flow Reaction

In continuous multiphase flow photochemical reactions, the generation of insoluble materials can significantly reduce the efficiency of material and light energy transfer between interfaces due to numerous interfaces within the hybrid system. The problem of solids blocking pipelines further compounds this issue. This study presents the design and construction of an optical-ultrasonic coupled continuous flow reactor to synthesize the insoluble α-bromoketone (4,4′-bis­(2-bromoacetyl)­biphenyl) is continuously produced in situ for synthesis, eliminating the need for large quantities of toxic bromine. A flowing cooling medium enhanced the ultrasound power transfer and eliminated the thermal effects of the ultrasound and light sources under TR = 2.1 min, T = 20 °C, and a flow cooling medium thickness of 1.5 cm. The reactants were converted to 92.4% and yielded up to 90.2%, significantly better than the batch reactor results. The experimental results show that the product particles are reduced considerably under ultrasound, eliminating the blockage. Free radical capture experiments investigated the stepwise bromination mechanism, kinetic parameters were calculated, and the reaction rate expressions derived from the basic steps were consistent with the kinetic model. These findings provide valuable insights into the reaction process, contributing to a more comprehensive understanding

Copper-Based Integral Catalytic Impeller for the Rapid Catalytic Reduction of 4‑Nitrophenol

The integral catalytic impeller can simultaneously improve reaction efficiency and avoid the problem of catalyst separation, which has great potential in applying heterogeneous catalysis. This paper introduced a strategy of combining electroless copper plating with 3D printing technology to construct a pluggable copper-based integral catalytic agitating impeller (Cu-ICAI) and applied it to the catalytic reduction of 4-nitrophenol (4-NP). The obtained Cu-ICAI exhibits very excellent catalytic activity. The 4-NP conversion rate reaches almost 100% within 90 s. Furthermore, the Cu-ICAI can be easily pulled out from the reactor to be repeatedly used more than 15 times with high performance. Energy-dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy characterizations show that the catalyst obtained by electroless copper plating is a ternary Cu-Cu2O-CuO composite catalyst, which is conducive to the electron transfer process. This low-cost, facile, and versatile strategy, combining electroless plating and 3D printing, may provide a new idea for the preparation of the integral impeller with other metal catalytic activities

Improved Water Collection from Short-Term Fog on a Patterned Surface with Interconnected Microchannels

Fog harvesting is considered a promising freshwater collection strategy for overcoming water scarcity, because of its environmental friendliness and strong sustainability. Typically, fogging occurs briefly at night and in the early morning in most arid and semiarid regions. However, studies on water collection from short-term fog are scarce. Herein, we developed a patterned surface with highly hydrophilic interconnected microchannels on a superhydrophobic surface to improve droplet convergence driven by the Young–Laplace pressure difference. With a rationally designed surface structure, the optimized water collection rate from mild fog could reach up to 67.31 g m–2 h–1 (6.731 mg cm–2 h–1) in 6 h; this value was over 130% higher than that observed on the pristine surface. The patterned surface with interconnected microchannels significantly shortened the startup time, which was counted from the fog contact to the first droplet falling from the fog-harvesting surface. The patterned surface was also facilely prepared via a controllable strategy combining laser ablation and chemical vapor deposition. The results obtained in outdoor environments indicate that the rationally designed surface has the potential for short-term fog harvesting. This work can be considered as a meaningful attempt to address the practical issues encountered in fog-harvesting research