Field-Assisted Efficient Capturing and Analysis of Airborne Nanoparticulate Matter Using a Multifunctional Nanoporous Membrane.

As the potential adverse health and environmental effects of nanoscale pollutants have garnered significant attention, the demand for monitoring and capturing ultrafine particulate matter has been growing. With the rise in ultrafine dust emissions, this issue has become increasingly important. However, submicron particles require advanced strategies to be captured because of their limited inertial effect. For example, electrostatic air filters have been investigated for their improved performance in the fine particle regime. On the other hand, Raman spectroscopy was proposed as a promising analytical strategy for aerosol particles because it can be used to conveniently detect analytes in a label-free manner. Thus, the synergistic integration of these strategies can open new applications for addressing environment-related challenges. This study presents a multifunctional approach for achieving both air filtration and surface-enhanced Raman scattering (SERS) for analyte identification. We propose a nanoporous membrane composed of a thin gold layer, copper, and copper oxide to provide the desired functions. The structures are produced by performing scalable electrodeposition and subsequent electron-beam evaporation, attaining an excellent filtration efficiency of 95.9% with an applied voltage of 5 kV for 300 nm KCl particles and a pressure drop of 121 Pa. Raman intensity measurements confirm that the nanodendritic surface of the membrane intensifies the Raman signals and allows for the detection of 10 µL of nanoplastic particle dispersion with a concentration of 50 µg/mL. Rhodamine 6G aerosol stream with an approximate particle deposition rate of 0.040 × 106 mm-2·min-1 is also identified in a minimum detectable time of 50 s. The membrane is shown to be recyclable owing to its structural robustness in organic solvents. In addition, the fatigue resistance of the structure is evaluated through 22,000 iterative loading cycles at a pressure of 177 kPa. No performance degradation is observed after the fatigue loading.

Design, Fabrication, and Dynamic Analysis of a MEMS Ring Resonator Supported by Twin Circular Curve Beams.

In this paper, we present a compressive study on the design and development of a MEMS ring resonator and its dynamic behavior under electrostatic force when supported by twin circular curve beams. Finite element analysis (FEA)-based modeling techniques are used to simulate and refine the resonator geometry and transduction. In proper FEA or analytical modeling, the explicit description and accurate values of the effective mass and stiffness of the resonator structure are needed. Therefore, here we outlined an analytical model approach to calculate those values using the first principles of kinetic and potential energy analyses. The natural frequencies of the structure were then calculated using those parameters and compared with those that were simulated using the FEA tool ANSYS. Dynamic analysis was performed to calculate the pull-in voltage, shift of resonance frequency, and harmonic analyses of the ring to understand how the ring resonator is affected by the applied voltage. Additional analysis was performed for different orientations of silicon and assessing the frequency response and frequency shifts. The prototype was fabricated using the standard silicon-on-insulator (SOI)-based MEMS fabrication process and the experimental results for resonances showed good agreement with the developed model approach. The model approach presented in this paper can be used to provide valuable insights for the optimization of MEMS resonators for various operating conditions.

Electrostatic Force-Assisted Transfer of Flexible Silicon Photodetector Focal Plane Arrays for Image Sensors.

Flexible photodetectors are pivotal in contemporary optoelectronic technology applications, such as data reception and image sensing, yet their performance and yield are often hindered by the challenge of heterogeneous integration between photoactive materials and flexible substrates. Here, we showcase the potential of an electrostatic force-assisted transfer printing technique for integrating Si PIN photodiodes onto flexible substrates. This clean and dry process eliminates the need for chemical etchants, making it a highly desirable method for manufacturing high-performance flexible photodetector arrays, expanding their widespread applications in electronic eyes, robotics, and human-machine interaction. As a demonstration, a 5 × 5 flexible Si photodetector focal plane array is constructed for imaging sensors and shaped into a convex semicylindrical form to achieve a π field of view with long-term mechanical and thermal stability. Such an approach provides a high yield rate and consistent performance, with the single photodetector demonstrating exceptional characteristics, including a responsivity of 0.61 A/W, a response speed of 39.77 MHz, a linear dynamic range of 108.53 dB, and a specific detectivity of 2.75 × 1012 Jones at an applied voltage of -3 V at 940 nm.

Heterodyne High-Harmonic Electrostatic Force Microscopy with Improved Spatial Resolution for Nanoscale Identification of Metallic/Semiconducting Carbon Nanotubes.

There are two main types of carbon nanotubes (CNTs): metallic and semiconducting. Naturally grown CNTs are randomly distributed, posing challenges in distinguishing between the two types. Here, a novel approach for nanoscale high-resolution imaging and identification of CNTs was introduced by incorporating the heterodyne technique into high-harmonic electrostatic force microscopy (HH-EFM) on an atomic force microscopy (AFM) platform. In the developed heterodyne HH-EFM, a more localized high-order gradient of tip-sample nonlinear interaction force is used as signal channels, resulting in an improved spatial resolution, compared to the conventional HH-EFM. Furthermore, the heterodyne HH-EFM also has the capability to visualize material carrier density and assess qualitative carrier transport performance. Our work not only presents a new approach to identifying/exploring electrical properties of low-dimensional nanomaterials but also provides a solution for optimizing resolution in long-range interaction-based functional AFM technologies.

Portable Triboelectric Electrostatic Tweezer for External Manipulation of Droplets within a Closed Femtosecond Laser-Treated Superhydrophobic System.

Controllable droplet manipulation has diverse applications; however, limited methods exist for externally manipulating droplets in confined spaces. Herein, we propose a portable triboelectric electrostatic tweezer (TET) by integrating electrostatic forces with a superhydrophobic surface that can even manipulate droplets in an enclosed space. Electrostatic induction causes the droplet to be subjected to an electrostatic force in an electrostatic field so that the droplet can be moved freely with the TET on a superhydrophobic platform. Characterized by its high precision, flexibility, and robust binding strength, TET can manipulate droplets under various conditions and achieve a wide range of representative fluid applications such as droplet microreactors, precise self-cleaning, cargo transportation, the targeted delivery of chemicals, liquid sorting, soft droplet robotics, and cell labeling. Specifically, TET demonstrated the ability to manipulate internal droplets from the outside of a closed system, such as performing cell labeling experiments within a sealed Petri dish without opening the culture system.

Antibacterial and Antibiofouling Activities of Carbon Polymerized Dots/Polyurethane and C60/Polyurethane Composite Films.

The cost of treatment of antibiotic-resistant pathogens is on the level of tens of billions of dollars at the moment. It is of special interest to reduce or solve this problem using antimicrobial coatings, especially in hospitals or other healthcare facilities. The bacteria can transfer from medical staff or contaminated surfaces to patients. In this paper, we focused our attention on the antibacterial and antibiofouling activities of two types of photodynamic polyurethane composite films doped with carbon polymerized dots (CPDs) and fullerene C60. Detailed atomic force, electrostatic force and viscoelastic microscopy revealed topology, nanoelectrical and nanomechanical properties of used fillers and composites. A relationship between the electronic structure of the nanocarbon fillers and the antibacterial and antibiofouling activities of the composites was established. Thorough spectroscopic analysis of reactive oxygen species (ROS) generation was conducted for both composite films, and it was found that both of them were potent antibacterial agents against nosocomial bacteria (Klebsiela pneumoniae, Proteus mirabilis, Salmonela enterica, Enterococcus faecalis, Enterococcus epidermis and Pseudomonas aeruginosa). Antibiofouling testing of composite films indicated that the CPDs/PU composite films eradicated almost completely the biofilms of Pseudomonas aeruginosa and Staphylococcus aureus and about 50% of Escherichia coli biofilms.

Weak Electrostatic Force on K+ in Gel Polymer Electrolyte Realizes High Ion Transference Number for Quasi Solid-State Potassium Ion Batteries.

Quasi-solid-state potassium-ion batteries (SSPIBs) are of great potential for commercial use due to the abundant reserves and cost-effectiveness of resources, as well as high safety. Gel polymer electrolytes (GPEs) with high ionic conductivity and fast interfacial charge transport are necessary for SSPIBs. Here, the weak electrostatic force between K+ and electronegative functional groups in the ethoxylated trimethylolpropane triacrylate (ETPTA) polymer chains, which can promote fast migration of free K+, is revealed. To further enhance the interfacial reaction kinetics, a multilayered GPE by in situ growth of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) on ETPTA (PVDF-HFP|ETPTA|PVDF-HFP) is constructed to improve the interface contact and provide sufficient K+ concentration in PVDF-HFP. A high ion transference number (0.92) and a superior ionic conductivity (5.15 × 10-3 S cm-1) are achieved. Consequently, the SSPIBs with both intercalation-type (PB) and conversion-type (PTCDA) cathodes show the best battery performance among all reported SSPIBs of the same cathode. These findings demonstrate that potassium-ion batteries have the potential to surpass Li/Na ion batteries in solid-state systems.

Water-compatible cross-linked pyrrolidone acrylate pressure-sensitive adhesives with persistent adhesion for transdermal delivery: Synergistic effect of hydrogen bonding and electrostatic force.

Poor skin adhesion and mechanical properties are common problems of pressure-sensitive adhesive (PSA) in transdermal drug delivery system (TDDS). Its poor water compatibility also causes the patch to fall off after sweating or soaking in the application site. To solve this problem, poly (2-Ethylhexyl acrylate-co-N-Vinyl-2-pyrrolidone-co-N-(2-Hydroxyethyl)acrylamide) (PENH), a cross-linked pyrrolidone polyacrylate PSA, was designed to improve the adhesion and water resistance of PSA through electrostatic force and hydrogen bonding system. The structure of PENH was characterized by 1H NMR, FTIR, DSC, and other methods. The mechanism was studied by FTIR, rheological test, and molecular simulation. The results showed that the PENH patch could adhere to human skin for more than 10 days without cold flow, and it could still adhere after sweating or water contact. In contrast, the commercial PSA Duro-Tak® 87-4098 and Duro-Tak® 87-2852 fell off completely on the 3rd and 6th day, respectively, and Duro-Tak® 87-2510 showed a significant dark ring on the second day. Mechanism studies have shown that the hydrogen bond formed by 2-ethylhexyl acrylate (2-EHA), N-vinyl-2-pyrrolidinone (NVP), and N-(2-Hydroxyethyl)acrylamide (HEAA) enhances cohesion, the interaction with skin improves skin adhesion, and the electrostatic interaction with water or drug molecules enhances the ability of water absorption and drug loading. Due to the synergistic effect of hydrogen bonds and electrostatic force, PENH can maintain high cohesion after drug loading or water absorption. PENH provides a choice for the development of water-compatible patches with long-lasting adhesion. STATEMENT OF SIGNIFICANCE: Based on the synergistic effect of hydrogen bonding and electrostatic force, a hydrogen-bonded, cross-linked pyrrolidone acrylate pressure-sensitive adhesive for transdermal drug delivery was designed and synthesized, which has high adhesion and cohesive strength and is non-irritating to the skin. The patch can be applied on the skin surface continuously for more than 10 days without the phenomenon of "dark ring", and the patch can remain adherent after the patient sweats or bathes. This provides a good strategy for choosing a matrix for patches that require prolonged administration.

Instability of membranes containing ionizable cationic lipids: Effects of the repulsive range of headgroups and tail structures.

The stability of membranes formed by ionizable cationic lipids, which constitute the primary components in lipid nanoparticles capable of endosomal escape, is explored using coarse-grained dissipative particle dynamics. Three types of ionizable model lipids with different tail structures are considered. Endosome acidification causes the ionization of lipids, leading to an increased repulsive range between their headgroups. When electrostatic repulsion is modeled as a conservative force with a long-range cutoff distance (rc,HH), the membrane and vesicle experience a loss of structural integrity and develop holes as rc,HH is beyond a critical value, which varies with the tail structure. When Coulombic repulsion is explicitly incorporated and intensified, a fully ionized lipid membrane undergoes a loss of structural integrity, displaying a qualitative similarity to the effect observed with the increase in rc,HH on the membrane stability. Qualitatively similar results are obtained for partially ionized membranes as the fraction of charged lipids increases. The stability of a mixed lipid membrane containing both ionizable and conventional lipids is also investigated. The disruption of the bilayer structure occurs for a sufficiently high charged fraction. The membrane instability can be attributed to the decrease in the packing parameter, which significantly deviates from unity as the interaction range increases.

The physical-mechanical behavior and chemical bonding nature of poly-N-vinylpyrrolidone modified cement concrete.

In this study, the various amounts of poly-N-vinylpyrrolidone (PVPr) were added to the cement paste, and some parameters - flowing, initial and final setting points, water absorption, compressive strength, and flexural strength were determined. The concrete containing 0.8% PVPr exhibited high water absorption, specifically, at 14 and 28 days, increased from 15.65% to 20.71% and from 16.74% to 21.67%, respectively. The final setting time increased from 238 min to 261 min. It was determined that the compressive strength of the cement mortar increased from 54.8 MPa to 58.5 MPa when the PVPr content was 0.8-1.0%. The flexural strength also improved due to the presence of PVPr, increasing from 11.58 MPa to 14.27 MPa. According to the FTIR characterization, the PVPr macromolecule interacts with Ca2+ and Al3+ ions. TGA analysis reveals that the chemical interaction of PVPr with calcium and aluminum ions limits its mass loss up to 4-5% until 400 °C.

On-Demand, Contact-Less and Loss-Less Droplet Manipulation via Contact Electrification.

While there are many droplet manipulation techniques, all of them suffer from at least one of the following drawbacks - complex fabrication or complex equipment or liquid loss. In this work, a simple and portable technique is demonstrated that enables on-demand, contact-less and loss-less manipulation of liquid droplets through a combination of contact electrification and slipperiness. In conjunction with numerical simulations, a quantitative analysis is presented to explain the onset of droplet motion. Utilizing the contact electrification technique, contact-less and loss-less manipulation of polar and non-polar liquid droplets on different surface chemistries and geometries is demonstrated. It is envisioned that the technique can pave the way to simple, inexpensive, and portable lab on a chip and point of care devices.

Imaging the Quantum Capacitance of Strained MoS2 Monolayers by Electrostatic Force Microscopy.

We implemented radio frequency-assisted electrostatic force microscopy (RF-EFM) to investigate the electric field response of biaxially strained molybdenum disulfide (MoS2) monolayers (MLs) in the form of mesoscopic bubbles, produced via hydrogen (H)-ion irradiation of the bulk crystal. MoS2 ML, a semiconducting transition metal dichalcogenide, has recently attracted significant attention due to its promising optoelectronic properties, further tunable by strain. Here, we take advantage of the RF excitation to distinguish the intrinsic quantum capacitance of the strained ML from that due to atomic scale defects, presumably sulfur vacancies or H-passivated sulfur vacancies. In fact, at frequencies fRF larger than the inverse defect trapping time, the defect contribution to the total capacitance and to transport is negligible. Using RF-EFM at fRF = 300 MHz, we visualize simultaneously the bubble topography and its quantum capacitance. Our finite-frequency capacitance imaging technique is noninvasive and nanoscale and can contribute to the investigation of time- and spatial-dependent phenomena, such as the electron compressibility in quantum materials, which are difficult to measure by other methods.