Effective surface area on rough substrates for bacterial adhesion is examined by analyzing the solid area fraction of surfaces, where the bacterial medium is in contact with the solid surface.

Particulate respirators have been used in both general environments and in the workplace. Despite the existence of certified respirators for workers, no strict regulations exist for masks worldwide. The aims of this study were to evaluate the filter efficiency of various mask types using the Korean Food and Drug Administration (KFDA) [similar to the European Union (EU) protocol] and the National Institute for Occupational Safety and Health (NIOSH) protocol and to compare the test results. We tested a total of 44 mask brands of four types (anti-yellow sand, medical, quarantine, general) and handkerchiefs with a TSI 8130 Automatic Filter Tester. A wide variation of penetration and pressure drops was observed by mask types. The overall mean penetration and pressure drop of all tested masks were respectively 35.6 ± 34.7%, 2.7 ± 1.4 mm H 2 O with the KFDA protocol, and 35.1 ± 35.7%, 10.6 ± 5.88 mm H 2 O with the NIOSH protocol. All tested quarantine masks satisfied the KFDA criterion of 6%. Six-ninths and four-sevenths of the anti-yellow sand masks for adults and children satisfied the criterion of 20%, respectively. Medical masks, general masks, and handkerchiefs were found to provide little protection against respiratory aerosols.

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Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.

Cellulose nanoparticles obtained by acid hydrolysis of cellulose paper were used to reinforce polystyrene composite films. The nonionic surfactant sorbitan monostearate was utilized to improve the dispersion properties of the hydrophilic cellulose in hydrophobic matrix and to prevent the formation of aggregates. Turbidity tests were used to measure dispersion stability of the cellulose crystallites in the hydrophobic solvent used in the composite manufacture. A correlation was found between the dispersion stability in solvent and the formation of aggregates in the polymeric composites. Nanocomposite films were processed using a casting/evaporation technique. Thermal and mechanical properties of processed composites were studied by differential scanning calorimetry (DSC) and dynamical mechanical analyses (DMA), respectively. The results showed that the optimum addition of surfactant produced better dispersion of the cellulose particles in the polystyrene matrix and improved the mechanical properties of the resulting composite due to an enhanced compatibility. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The wetting behavior of a hydrophobic rough surface is investigated on a surface fabricated by applying low surface tension materials such as silicone or fluoropolymer to polyester woven fabric consisting of multifilament yarns. The roughness factor of various woven fabrics can be calculated by Wenzel's and Cassie-Baxter's equations. For the fabrics treated with silicone or fluoropolymer, the Cassie-Baxter model was applied, showing a level of agreement for the fabric specimens non-textured filament fibers between the predicted contact angles and the measured values. More precisely, the fabrics treated with silicone or fluoropolymer represent the transitional state between the Wenzel type and the Cassie-Baxter type; that is, the fractional contact area between the water and air f 2 is greater than zero, and the sum of the fractional contact areas for solid-water f 1 and air-water f 2 is greater than 1. A surface with lower energy and higher roughness gave f 1 + f 2 close to 1 with smaller f 1 and larger f 2 , which resulted in a high contact angle. KeywordsHydrophobic, lotus effect, roughness factor, Wenzel model, Cassie-Baxter model Inspired by natural surfaces like the lotus leaf, surfaces with extreme water repellent properties have received considerable interest in the last decade. 1 The studies by Wenzel 2 and Cassie and Baxter 3 showed that the rough and porous structure of a surface combined with a low surface energy can contribute to the hydrophobicity of a surface. The surface of the lotus leaf is chemically made of wax and structurally has two levels of roughness consisting of nano-scale bumps on the surface of micro-scale protrusions that enables the trapping of air underneath water droplets, thereby contributing to a well-designed superhydrophobic surface. 4 Drops of water deposited on such superhydrophobic surfaces exhibit extremely high contact angles (>150 ) and roll off at slight inclinations. Potential applications range from non-wettable, quick-drying surfaces to anti-fouling or self-cleaning surfaces. 4-8 In view of the significant potential of such surfaces for numerous scientific and industrial applications, many strategies to create superhydrophobic surfaces have been published to date. [6][7][8][9] As a measure of the hydrophobicity of the fabric surface, the static contact angle is often used; a larger contact angle with a smaller contact angle hysteresis represents higher hydrophobicity. Wenzel 2 and Cassie and Baxter 3 suggested the theoretical models for contact angles of a liquid on a surface with certain geometry. 9 Different contact angles may result with the same roughness texture depending on how the liquid is configured on the surface. When a liquid completely fills all the spaces in the pores, the Wenzel model is applied to describe the contact angle W r as a function of the ratio of the liquid-solid contact area to the

Electret filters as opposed to mechanical filters display the enhanced ability to capture airborne particles with the electrostatic attraction. However, the environmental aging during shelf-life or use may cancel its benefit by dissipating the charges. This work investigates the polymeric attributes influencing the charge decay and the electrostatic filtration of electret filters, employing polymers with different dielectric constants (εr) and wettability. As accelerated aging, high temperature (120 °C) or high humidity (25 °C, 90% RH) was applied to the electret filters for 48 h. For the humidity aging, wetting property of material was a critical factor affecting the charge decay and the filtration performance, as the absorbed water increases the electrical conductivity. For the thermal aging, the material with the highest εr deteriorated the electric potential and the filtration performance by the largest extent, due to the lower band gap energy for charge transfer. The results of this study implicate that εr and wettability are important material parameters influencing the electric conductivity and chain mobility, and they can be used as convenient predictors for charge retention capacity affecting the robust electrostatic filtration performance.