Electrostatic force distribution on an electrodynamic screen

The enormous potential of solar energy harvesting plants to provide clean energy is severely limited by dust accumulation on their optical surfaces. In lieu of the most commonly-practiced manual cleaning method of using high-pressure water jets, electrodynamic screen (EDS) technology offers an attractive solution for removing dust particles from optical surfaces using electrostatic forces. In this paper, the impacts of different EDS design parameters in the electric field distribution on an EDS have been studied. Furthermore, based on electric field expressions, closed-form solutions for multipolar dielectrophoretic (DEP) forces in the EDS application are provided. Detailed evaluation of the EDS performance necessitates investigation of different forces involved in the dust removal process. Different comparisons are made between repelling and attracting forces exerted on dust particles deposited on an EDS surface. These comparisons elucidate EDS performance in the removal of a given size range of dust particles. The significant detrimental impact of relative humidity upon the dust removal process is quantitatively addressed. It is shown how just a 10 percent increase in relative humidity can make the repelling force ineffective in the dust removal process.     

Enhancing the adhesion strength of micro electroforming layer by ultrasonic agitation method and the application

Micro electroforming is widely used for fabricating micro metal devices in Micro Electro Mechanism System (MEMS). However, there is the problem of poor adhesion strength between micro electroforming layer and substrate. This dramatically influences the dimensional accuracy of the device. To solve this problem, ultrasonic agitation method is applied during the micro electroforming process. To explore the effect of the ultrasonic agitation on the adhesion strength, micro electroforming experiments were carried out under different ultrasonic power (0 W, 100 W, 150 W, 200 W, 250 W) and different ultrasonic frequencies (0 kHz, 40 kHz, 80 kHz, 120 kHz, 200 kHz). The effects of the ultrasonic power and the ultrasonic frequency on the micro electroforming process were investigated by polarization method and alternating current (a.c.) impedance method. The adhesion strength between the electroforming layer and the substrate was measured by scratch test. The compressive stress of the electroforming layer was measured by X-ray Diffraction (XRD) method. The crystallite size of the electroforming layer was measured by Transmission Electron Microscopy (TEM) method. The internal contact surface area of the electroforming layer was measured by cyclic voltammetry (CV) method. The experimental results indicate that the ultrasonic agitation can decrease the polarization overpotential and increase the charge transfer process. Generally, the internal contact surface area is increased and the compressive stress is reduced. And then the adhesion strength is enhanced. Due to the different depolarization effects of the ultrasonic power and the ultrasonic frequency, the effects on strengthening the adhesion strength are different. When the ultrasonic agitation is 200 W and 40 kHz, the effect on strengthening the adhesion strength is the best. In order to prove the effect which the ultrasonic agitation can improve the adhesion strength of the micro devices, micro pillar arrays were fabricated under ultrasonic agitation (200 W, 40 kHz). The experimental results show that the residual rate of the micro pillar arrays is increased about 17% by ultrasonic agitation method. This work contributes to fabricating the electroforming layer with large adhesion strength.     

Multiscale dynamics of the cell envelope of Shewanella putrefaciens as a response to pH change

The bacterial surface properties of gram-negative Shewanella putrefaciens were characterized by microbial adhesion to hydrocarbons (MATH), adhesion to polystyrene dishes, and electrophoresis at different values of pH and ionic strength. The bacterial adhesion to these two apolar substrates shows significant variations according to pH and ionic strength. Such behavior could be partly explained by electrostatic repulsions between bacteria and the solid or liquid interface. However, a similar trend was also observed at rather high ionic strength where electrostatic interactions are supposed to be screened. The nanomechanical properties at pH 4 and 10 and at high ionic strength were investigated by using atomic force microscopy (AFM). The indentation curves revealed the presence of a polymeric external layer that swells and softens up with increasing pH. This suggests a concomitant increase of the water permeability and so did of the hydrophilicity of the bacterial surface. Such evolution of the bacterial envelope in response to changes in pH brings new insight to the pH dependence in the bacterial adhesion tests. It especially demonstrates the necessity to consider the hydrophobic/hydrophilic surface properties of bacteria as not univocal for the various experimental conditions investigated.     

Direct fluorination—Useful tool to enhance commercial properties of polymer articles

Fundamental features and industrial applications of the direct fluorination of polymers are reviewed. Fundamental features of the direct fluorination of a set of polymers, such as polystyrene, polyethyleneterephthalate, poly(2,6-dimethyl-1,4-phenylene oxide), PMMA, LDPE (two types), HDPE (six types), polyvinyltrimethylsilane, poly(4-methyl-pentene-1), polyimide Matrimid 5216^®, polysulfones, polyetheretherketone, polycarbonatesiloxane, polysulphone-polybuthadiene block-copolymers, polypropylene, PVF, PVDF, etc. are described. Influence of composition of the fluorinating mixture (F₂-He-N₂-O₂-HF), fluorine partial pressure, temperature and fluorination duration, on the rate of formation of the fluorinated layer and the chemical composition, density, refraction index, surface energy, gas separation properties and friction coefficient of fluorinated layer have been investigated. Processes of formation and termination of long-living and short-living radicals and grafting of acrylonitrile to fluorinated polymers have been studied. Industrial applications of the direct fluorination to enhance the commercial properties of polymeric goods, such as separation factor of polymeric membranes for gas separation, barrier properties of polymer vessels, pipes and packagings, adhesion, printability, wetting and transparency in visible and IR are reviewed.     

Expression of integrin β1 and its roles on adhesion between different cell cycle hepatocellular carcinoma cells (SMMC-7721) and human umbilical vein endothelial cells

To investigate expression of integrin β₁ and its roles on adhesion between different cell cycle hepatocellular carcinoma cell (HCC) and human umbilical vein endothelial cells (HUVEC), the synchronous G₁ and S phase HCC were achieved through thymine-2-deoxyriboside and colchicines sequential blockage method and double thymine-2-deoxyriboside blockage method, respectively. Expression of integrin β₁ on hepatocellular carcinoma cells was detected with flow cytometer. Further, the adhesive force of HCC to HUVEC and the role of integrin β₁ in this adhesive course were studied by micropipette aspiration technique. The results showed that percentage of each cyclic phases of the controlled HCC (non-synchronous) are: G₂+M phase, 11%; G₁ phase, 54%; S phase, 36%; the synchronous rates of G₁ and S phase HCC amount to 74 and 98%, respectively. The expressive fluorescent intensity of integrin β₁ in G₁ phase HCC is depressed significantly than the values of S phase and controlled HCC. Accordingly, the adhesive forces of G₁ phase HCC to HUVEC was significantly lower than the value of S phase cells (P<0.01), but it has no remarkable difference when compared the adhesive force values of S phase HCC with control; the contribution of integrin β₁ was about 50% in the adhesion of HCC to HUVEC. It suggested that HCC would be synchronized preferably in G₁ and S phase with thymine-2-deoxyriboside and colchicines, the adhesive molecule integrin β₁ expressed in a high lever in HCC and presented differences in vary cell cycle, and integrin β₁ played an important roles in adhesion of HCC to HUVEC. Possibly, S phase HCC take a great action in this adhesive course.     

Electrically conductive composites of polyethylene filled with polyamide particles coated with silver

New types of electrically conductive polymeric composites were prepared on a base of high-density polyethylene (HDPE) matrix filled with silver-coated polyamide (PA) particles. The electrical, mechanical and adhesive properties of those composites are reported in this paper. The percolation concentration of the filler within a matrix was found to be 4 vol.%. Composites filled with high filler content were highly electrically conductive; their electrical conductivity reached the value of 6.8 × 10² S cm⁻¹. Mechanical properties and rheology of these composites were discussed. The adhesive properties of the composites to metal sharply increased with an increase in the filler content.     

Stability of mechanical properties of molecular layer–deposited alucone

We report on the effect of aging on the mechanical properties of molecular layer–deposited (MLD) thin films. We studied the mechanical failure of the films during uniaxial tensile testing and observed a sixfold difference in the crack-onset strain (COS) and related flexibility within the first two days after the samples were exposed to ambient air. The MLD films made using trimethylaluminum and ethylene glycol are notorious for exhibiting structural changes after the fabrication; we show that these changes are detrimental for mechanical robustness of the films. This information aids to plan the handling or the protection of these films to achieve better performance with these materials. The interfacial shear strains and COSs of the shortly air-exposed 300-nm-thick films were observed to be roughly 0.3% and 1.8%, respectively. These values are the highest reported so far for hybrid organic–inorganic MLD thin films and would extrapolate to about 14% COS for 5-nm-thick film, indicating potential applications as interfacial adhesion layer for films on polymer substrates and as a protective coating in battery applications.     

透明质酸的浓度对成纤维细胞黏附和增殖的影响

透明质酸广泛存在于细胞外基质、细胞表面和细胞内部,其独特的理化特性使其具有多种生物学功能。透明质酸对细胞具有多种作用,可以调控细胞生长因子和细胞因子的分泌,抑制蛋白酶的分解,影响细胞的黏附、生长、增殖和分化。本实验将不同浓度的透明质酸加入成纤维细胞培养液中,考察了在培养液中透明质酸的浓度对成纤维细胞的黏附、DNA合成量、糖胺聚糖分泌量和MTT活性的影响。实验结果表明,当培养液中透明质酸的浓度小于0.1%时,对成纤维细胞的黏附和生长增殖有明显的促进作用,当培养液中透明质酸的浓度大于0.1%时,对成纤维细胞的黏附和生长增殖有很强的抑制作用。     

In Situ Amperometric Characterization of Liposome Suspensions with Concomitant Oxygen Reduction

Amperometry of oxygen reduction at the dropping mercury electrode (DME) was applied for in situ characterization of liposome suspensions in terms of concentration, level of polydispersity and potential range of adhesion. Liposomes prepared from egg‐phosphatidylchloline/cholesterol/dicetylphosphate in the molar ratio of 7 : 5 : 1 were suspended in phosphate‐buffered saline (PBS). Adhesion signals of single liposomes in air‐saturated suspensions were detected in the broad potential range (from ?100 to ?1200 mV vs. 0.1 M Ag/AgCl reference electrode) as transient enhacements of oxygen reduction. Measured concentration range in air‐saturated suspensions was 10⁶–10⁸ liposomes/L.     

Effects of denaturation and association of collagen on adsorption behavior: two-dimensional nanostructure and its property

Effects of denaturation and association of collagen on adsorption behavior were studied in various pH and temperature T by a quartz crystal microbalance QCM. The surface nanostructure, the adhesion force F _ad, and the local frictional coefficient μ of collagen were studied by an atomic force microscope AFM and a lateral force microscope LFM. Adsorptions of collagen were Langmuir type in the regions of pH 3.0–5.8 and T = 25–50 °C. With increasing pH and T, adsorption mass Γ increased, and adsorbed fibrils increased in width. At interface, the association of collagen molecules in solution enhanced the formation of fibrils. The results of F _ad in the solution of pH 3.0 increased with increasing Γ and T but decreased in pH 5.8. The results of μ increased with increasing Γ and T, and those in pH 3.0, were much greater than those in pH 5.8. From comparing them with the results of bovine serum albumin and sodium hyaluronate monolayer, we concluded that nonelectrostatic interactions and the softness of collagen layer contribute primarily to F _ad and μ.