Observation of morphological relaxation of copper and silver electrodes in solution using a quartz microbalance

Oxidation of smooth copper and silver surfaces leads to roughening which persists when the oxide layers are reduced. Furthermore, the roughened surface is observed to relax on a time scale of hours when potentiostated at reductive potentials. Reconstruction was monitored in-situ by differential capacitance and a quartz microbalance oscillating in solution. Scanning electron microscopy (SEM) gave supporting evidence. Estimates of the surface roughness of the oxide layers and the bare metal were obtained from the microbalance data.     

Combined solid state NMR and X-ray diffraction investigation of the local structure of the five-coordinate silicon in fluoride-containing as-synthesized STF zeolite

The local structure of the [SiO(4/2)F]- unit in fluoride-containing as-synthesized STF zeolite has been experimentally determined by a combination of solid-state NMR and microcrystal X-ray diffraction to be very close to trigonal bipyramidal. Because the fluoride ions are disordered over two sites, the resulting local structure of the [SiO(4/2)F]- unit from a conventional XRD refinement is an average between tetrahedral SiO(4/2) and five-coordinate [[SiO(4/2)F]-, giving an apparent F-Si distance longer than expected. The correct F-Si distance was determined by slow spinning MAS and fast spinning (19)F/(29)Si CP and REDOR solid-state NMR experiments and found to be between 1.72 and 1.79 A. In light of this, the X-ray structure was re-refined, including the disorder at Si3. The resulting local structure of the [SiO(4/2)F]- unit was very close to trigonal bipyramidal with a F-Si distance of 1.744 (6) A, in agreement with the NMR results and the prediction of Density Functional Theory calculations. In addition, further evidence for the existence of a covalent F-Si bond is provided by a (19)F-->(29)Si refocused INEPT experiment. The resonance for the five-coordinate species at -147.5 ppm in the (29)Si spectrum is a doublet due to the (19)F/(29)Si J-coupling of 165 Hz. The peaks in this doublet have remarkably different effective chemical shift anisotropies due to the interplay of the CSA, dipolar coupling, and J-coupling tensors. The distortions from tetrahedral geometry of the neighboring silicon atoms to the five-coordinate Si3 atom are manifested in increased delta(aniso) values. This information, along with F-Si distances measured by (19)F-->(29)Si CP experiments, makes it possible to assign half of the (29)Si resonances to unique tetrahedral sites. As well as determining the local geometry of the [SiO(4/2)F]- unit, the work presented here demonstrates the complementarity of the solid-state NMR and X-ray diffraction techniques and the advantages of using them together.     

Effect of oxidation on the wettability of poly(dimethylsiloxane) surfaces

The wetting of amorphous poly(dimethylsiloxane) (PDMS) surfaces by water has been studied using molecular dynamics simulations. PDMS surfaces were generated by compressing a long PDMS chain between two elastic boundaries at atmospheric pressure. Oxidation of the PDMS surface, achieved in real systems by exposure to air plasma or corona discharge, was modeled by replacing methyl groups on the PDMS chain with hydroxyl groups. Three surfaces of varying degrees of oxidation were characterized by measuring the water contact angle and the roughness. The dependence of the microscopic contact angle on drop size was measured from time averaged density profiles. The macroscopic contact angle was measured directly using a cylindrical drop of infinite length with zero contact line curvature. The measured macroscopic contact angle ranged from approximately 125 degrees on the untreated surface to 75 degrees on the most oxidized surface studied. The line tension was found to increase with increasing degree of oxidation, from a negligible value on the untreated surface to approximately 5x10(-11) J m(-1) on the most heavily oxidized surface.     

Surface functionalization of silicone rubber for permanent adhesion improvement

The surface properties of poly(dimethyl siloxane) (PDMS) layers screen printed onto silicon wafers were studied after oxygen and ammonia plasma treatments and subsequent grafting of poly(ethylene -alt-maleic anhydride) (PEMA) using X-ray photoelectron spectroscopy (XPS), roughness analysis, and contact angle and electrokinetic measurements. In the case of oxygen-plasma-treated PDMS, a hydrophilic, brittle, silica-like surface layer containing reactive silanol groups was obtained. These surfaces indicate a strong tendency for "hydrophobic recovery" due to the surface segregation of low-molecular-weight PDMS species. The ammonia plasma treatment of PDMS resulted in the generation of amino-functional surface groups and the formation of a weak boundary layer that could be washed off by polar liquids. To avoid the loss of the plasma modification effect and to achieve stabilization of the mechanically instable, functionalized PDMS top layer, PEMA was subsequently grafted directly or after using gamma-APS as a coupling agent on the plasma-activated PDMS surfaces. In this way, long-time stable surface functionalization of PDMS was obtained. The reactivity of the PEMA-coated PDMS surface caused by the availability of anhydride groups could be controlled by the number of amino functional surface groups of the PDMS surface necessary for the covalent binding of PEMA. The higher the number of amino functional surface groups available for the grafting-to procedure, the lower the hydrophilicity and hence the lower the reactivity of the PEMA-coated PDMS surface. Additionally, pull-off tests were applied to estimate the effect of surface modification on the adhesion between the silicone rubber and an epoxy resin.     

Characterization of CuInS2 Thin Films with Different Cu/In Ratio

Thin films of CuInS₂ were grown on glass substrate by successive ionic layer adsorption and reaction method with different [Cu]/[In] ratios and annealed at 400 °C for 30 min. The crystal structure and grain sizes of the thin films were characterized by X-ray diffraction method. Atomic force microscopy was used to determine surface morphology of the films. Optical and electrical properties of these films were investigated as a function of [Cu]/[In]ratios. The electrical resistivity of CuInS₂ of thin films was determined using a direct current-two probe method in the temperature range of 300—470 K. It is observed that, the electrical resistivity values show a big decreasing with increasing [Cu]/[In] ratio. Hence, the [Cu]/[In] ratio in the solution can drastically affect the structural, electrical, and optical properties of thin films of CuInS₂.     

Scalar coupling across [C-H···F-C] interactions in (σ-aryl)-chelating post-metallocenes

The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species.     

Cell and protein compatibility of parylene-C surfaces

Parylene-C, which is traditionally used to coat implantable devices, has emerged as a promising material to generate miniaturized devices due to its unique mechanical properties and inertness. In this paper we compared the surface properties and cell and protein compatibility of parylene-C relative to other commonly used BioMEMS materials. We evaluated the surface hydrophobicity and roughness of parylene-C and compared these results to those of tissue culture-treated polystyrene, poly(dimethylsiloxane) (PDMS), and glass. We also treated parylene-C and PDMS with air plasma, and coated the surfaces with fibronectin to demonstrate that biochemical treatments modify the surface properties of parylene-C. Although plasma treatment caused both parylene-C and PDMS to become hydrophilic, only parylene-C substrates retained their hydrophilic properties over time. Furthermore, parylene-C substrates display a higher degree of nanoscale surface roughness (>20 nm) than the other substrates. We also examined the level of BSA and IgG protein adsorption on various surfaces and found that surface plasma treatment decreased the degree of protein adsorption on both PDMS and parylene-C substrates. After testing the degree of cell adhesion and spreading of two mammalian cell types, NIH-3T3 fibroblasts and AML-12 hepatocytes, we found that the adhesion of both cell types to surface-treated parylene-C variants were comparable to standard tissue culture substrates, such as polystyrene. Overall, these results indicate that parylene-C, along with its surface-treated variants, could potentially be a useful material for fabricating cell-based microdevices.     

A new class of SN2 reactions catalyzed by protic solvents: Facile fluorination for isotopic labeling of diagnostic molecules

Aprotic solvents are usually preferred for the SN2 reactions, because nucleophilicity and hence SN2 reactivity are severely retarded by the influence of the partial positive charge of protic solvents. In this work, we introduce a remarkable effect of using tertiary alcohols as a reaction medium for nucleophilic fluorination with alkali metal fluorides. In this novel synthetic method, the nonpolar protic tert-alcohol enhances the nucleophilicity of the fluoride ion dramatically in the absence of any kind of catalyst, greatly increasing the rate of the nucleophilic fluorination and reducing formation of byproducts (such as alkenes, alcohols, or ethers) compared with conventional methods using dipolar aprotic solvents. The great efficacy of this method is a particular advantage in labeling radiopharmaceuticals with [18F]fluorine (t1/2 = 110 min) for positron emission tomographic (PET) imaging, and it is illustrated by the synthesis of four [18F]fluoride-radiolabeled molecular imaging probes-[18F]FDG, [18F]FLT, [18F]FP-CIT, and [18F]FMISO-in high yield and purity and in shorter times compared to conventional syntheses.     

The stability of radio-frequency plasma-treated polydimethylsiloxane surfaces

Polydimethylsiloxane (PDMS) is a widely used material for manufacturing lab-on-chip devices. However, the hydrophobic nature of PDMS is a disadvantage in microfluidic systems. To transform the hydrophobic PDMS surface to hydrophilic, it was treated with radio-frequency (RF) air plasma at 150, 300, and 500 mTorr pressures for up to 30 min. Following the surface treatment, the PDMS specimens were stored in air, deionized water, or 0.14 M NaCl solution at 4 degrees C, 20 degrees C, and 70 degrees C. The change in the hydrophilicity (wettability) of the PDMS surfaces was followed by contact angle measurements and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy as a function of time. As an effect of the RF plasma treatment, the contact angles measured on PDMS surfaces dropped from 113 +/- 4 degrees to 9 +/- 3 degrees . The chamber pressure and the treatment time had no or negligible effect on the results. However, the PDMS surface gradually lost its hydrophilic properties in time. The rate of this process is influenced by the difference in the dielectric constants of the PDMS and its ambient environment. It was the smallest at low temperatures in deionized water and largest at high temperatures in air. Apparently, the OH groups generated on the PDMS surface during the plasma treatment tended toward a more hydrophilic/less hydrophobic environment during the relaxation processes. The correlation between the FTIR-ATR spectral information and the contact angle data supports this interpretation.     

Facile creation of hierarchical PDMS microstructures with extreme underwater superoleophobicity for anti-oil application in microfluidic channels

Composition modification and surface microstructures have been widely utilized in interface science to improve the surface performance. In this paper, we observed a significant improvement of oil contact angle (CA) from 66 ± 2° to 120 ± 4° by introducing a radical silanol group on a flat PDMS surface through oxygen plasma pretreatment. By combining surface microstructures and plasma modification, we produced three kinds of superoleophobic surfaces: 20 μm pitch micropillar arrays, 2.5 μm pitch micropillar arrays and gecko foot-like hierarchical microstructures. Among them, the hierarchical surface with high surface roughness showed extreme underwater superoleophobicity, which featured ultrahigh CA (175 ± 3°) and ultrasmall sliding angle (<1°). Quantitative measurements demonstrated that these superoleophobic surfaces exhibited distinct adhesive behaviors, by which they were interpreted as Wenzel's, Cassie's and the Lotus state, respectively. A microfluidic channel with superoleophobic microstructures was further created by novel curve-assisted imprint lithography, and the characterization based on anti-oil contamination applications was carried out and discussed. We believe that the superoleophobic surfaces will power broad applications in oil microdroplet transportation, anti-oil channels and droplet microfluidic systems.     

Surface modification of a liquid‐crystalline polymer for copper metallization

The effects of different surface modifications on the adhesion of copper to a liquid‐crystalline polymer (LCP) were investigated with X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, contact‐angle measurements, and pull tests. High pull‐strength values were achieved when copper was sputter‐deposited onto plasma and reactive‐ion‐etching (RIE)‐pretreated LCP surfaces. The values were comparable to the reference pull strengths obtained with laminated copper on the LCP. The adhesion was relatively insensitive to the employed feed gas in the pretreatments. The surface characterizations revealed that for RIE and plasma treatments, the enhanced adhesion was attributable to the synergistic effects of the increased surface roughness and polar component of the surface free energy of the polymer. However, if the electroless copper deposition was performed on RIE‐ or plasma‐treated surfaces, very poor adhesion was measured. Good adhesion between the LCP substrate and electrolessly deposited copper was achieved only in the case of wet‐chemical surface roughening as a result of the creation of a sufficient number of mechanical interlocking sites, together with a significant loss of oxygen functionalities, on the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 623–636, 2003     

Fabrication of biomimetic superhydrophobic surfaces by a simple flame treatment method

A simple flame treatment method was explored to construct micro/nanostructures on a surface and then fabricate a biomimetic superhydrophobic surface at a relatively low cost. SiO₂‐containing polydimethylsiloxane (PDMS) was used as a substrate. The PDMS replicas with various micropatterned surfaces were fabricated using grass leaf, sand paper, and PET sheet with parallel groove geometry as templates via PDMS replica molding. The PDMS replica surfaces with micron structures and the surface of a flat PDMS sheet as a control sample were further treated by flame. The fabricated surfaces were characterized by scanning electron microscopy and water contact angle measurements. The effect of surface microstructures on the transparency of PDMS was also investigated. The studies indicate that the fine nanoscale structures can be produced on the surfaces of PDMS replicas and a flat PDMS sheet by a flame treatment method, and that the hierarchical surface roughness can be adjusted and controlled by varying the flame treatment time. The flame‐treated surfaces of PDMS replicas and a flat PDMS sheet possess superhydrophobicity and an ultra‐low sliding angle reaching a limiting value of 1°, and the anisotropic wettability of the PDMS replica surface with oriented microgroove structures can be greatly suppressed via flame treatment. The visible light transmittance of the flame‐treated flat PDMS surface decreases with prolonged flame treatment times. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrophilic surface modification of polydimetylsiloxane‐co‐2‐hydroxyethylmethacrylate (PDMS‐HEMA) by Silwet L‐77 (heptamethyltrisiloxane) surface treatment

Biomaterials and their host organism's quintessential place of interaction are the surfaces of materials, as transportation of liquids within microchannels requires hydrophilic surfaces. Modifying the hydrophobic surface of polydimethylsiloxane (PDMS) into a hydrophilic one which can be used in biomaterials remains a big challenge. Herein, PDMS‐hydroxyethylmethacrylate (HEMA) films were prepared by the condensation of PDMS using isophorone diisocyanate as a cross‐linker, followed by the incorporation of HEMA via radical copolymerization. The as‐prepared PDMS‐HEMA films were thereafter hydrophilized via physical treatment with heptamethyltrisiloxane. The surface properties of the obtained PDMS‐HEMA films were characterized in wettability, morphology, topography, swelling, mechanical properties, and protein adsorption. Compared to pristine PDMS‐HEMA as control, the surface wettability, roughness, and protein adsorption of the hydrophilized PDMS‐HEMA films were significantly improved while the films also exhibited excellent optical properties. However, the improvement of the swelling properties remains insignificant, indicating that the interior morphology was still based on the hydrophobic siloxane PDMS. The long‐term hydrophilicity was considered good as no significant hydrophobic recovery was noticeable in a period of 5 months after treatment.     

Friction and Adhesion of Gecko-Inspired PDMS Flaps on Rough Surfaces

Geckos have developed a unique hierarchical structure to maintain climbing ability on surfaces with different roughness, one of the extremely important parameters that affect the friction and adhesion forces between two surfaces. Although much attention has been paid on fabricating various structures that mimic the hierarchical structure of a gecko foot, yet no systematic effort, in experiment or theory, has been made to quantify the effect of surface roughness on the performance of the fabricated structures that mimic the hierarchical structure of geckos. Using a modified surface forces apparatus (SFA), we measured the adhesion and friction forces between microfabricated tilted PDMS flaps and optically smooth SiO(2) and rough SiO(2) surfaces created by plasma etching. Anisotropic adhesion and friction forces were measured when sliding the top glass surface along (+y) and against (-y) the tilted direction of the flaps. Increasing the surface roughness first increased the adhesion and friction forces measured between the flaps and the rough surface due to topological matching of the two surfaces but then led to a rapid decrease in both of these forces. Our results demonstrate that the surface roughness significantly affects the performance of gecko mimetic adhesives and that different surface textures can either increase or decrease the adhesion and friction forces of the fabricated adhesives.     

Surface modification of titanium with thermally treated polydimethylsiloxane coating and the effect on resin to titanium adhesion

In this study, titanium surface modification by a thermal treatment using a polydimethylsiloxane (PDMS) coating was investigated. The surfaces of four titanium samples were surface treated by polishing, sandblasting, and coating with a PDMS with a thermal treatment at 800 and 1100 °C. The titanium surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy. The effect of the surface treatments on adhesion of resin to titanium was assessed by shear adhesion strength test. XPS analysis showed that there was a change of elemental composition of titanium surfaces after surface treatment. Binding energy shifts for Si2p and O1s were observed after sandblasting and thermally treated PDMS. Therefore, chemical states of Si and O were changed. Atomic force microscopy analysis revealed that the surface topography of the Ti samples was different, and surface roughness was increased after sandblasting and thermal treatment of PDMS coating. Shear adhesion strength test results showed that the adhesion between resin and titanium is affected by the treatment temperature of PDMS coating. The highest adhesion is obtained at 1100 °C (14.7 ± 1.57 MPa). Copyright © 2014 John Wiley & Sons, Ltd.     

Stable superhydrophobic organic-inorganic hybrid films by electrostatic self-assembly

Organic-inorganic hybrid films were prepared through layer-by-layer (LBL) deposition of poly(allylamine hydrochloride) (PAH) and ZrO(2) nanoparticles coated with poly(acrylic acid) (PAA), allowing facile control of surface roughness and hydrophobicity. Superhydrophobic behavior was observed after deposition of silica nanoparticles and a simple fluorination of the surface. The structure of films was controlled by the number of deposition cycles using PAA-coated 100 nm ZrO(2) nanoparticles, the particle size, and the prelayer with PAH and PAA. The change in the apparent water contact angle of (PAH/PAA-coated ZrO(2)n surfaces without fluorination of the surface agrees with Cassie and Baxter's model for nonwetted surfaces even though the outermost surface itself is hydrophilic. Superhydrophobic surfaces were then successfully developed by the deposition of hydrophilic silica nanoparticles on a 10 bilayer surface of PAH/PAA-coated ZrO(2), and a simple fluorination. Moreover, the chemical stability of the film was greatly increased by heat-induced cross-linking of the film. The incorporation of ZrO(2) nanoparticles in superhydrophobic films promises better mechanical properties than the organic film.     

聚二甲基硅氧烷微流控芯片的紫外光照射表面处理研究

研究了紫外光化学表面改性对聚二甲基硅氧烷(PDMS)微流控芯片的片基间粘接力及毛细管通道电渗流性能的影响.PDMS片基经紫外光射照后,粘接力增强,可实现PDMS芯片的永久性封合,同时亲水性得到改善,通道中的电渗流增大.与文献报道的等离子体表面处理方法比较,采用紫外光表面处理,设备简单,操作方便,耗费少,是一种简单易行的聚二甲基硅氧烷芯片表面处理方法.     

A computational study of tetrafluoro-[2.2]cyclophanes

A computational study of the isomers of tetrafluorinated [2.2]cyclophanes persubstituted in one ring, namely F4-[2.2]paracyclophane (4), F4-anti-[2.2]metacyclophane (5a), F4-syn-[2.2]metacyclophane (5b), and F4-[2.2]metaparacyclophane (6a and 6b), was carried out. The effects of fluorination on the geometries, relative energies, local and global aromaticity, and strain energies of the bridges and rings were investigated. An analysis of the electron density by B3PW91/6-31+G(d,p), B3LYP/6-31+G(d,p), and MP2/6-31+G(d,p) was carried out using the natural bond orbitals (NBO), natural steric analysis (NSA), and atoms in molecules (AIM) methods. The analysis of frontier molecular orbitals (MOs) was also employed. The results indicated that the molecular structure of [2.2]paracyclophane is the most affected by the fluorination. Isodesmic reactions showed that the fluorinated rings are more strained than the nonfluorinated ones. The NICS, HOMA, and PDI criteria evidenced that the fluorination affects the aromaticity of both the fluorinated and the nonfluorinated rings. The NBO and NSA analyses gave an indication that the fluorination increases not only the number of through-space interactions but also their magnitude. The AIM analysis suggested that the through-space interactions are restricted to the F4-[2.2]metacyclophanes. In addition, the atomic properties, computed over the atomic basins, gave evidence that not only the substitution, but also the position of the bridges could affect the atomic charges, the first atomic moments, and the atomic volumes.     

Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the conditions of treatment with oxygen plasma

Treatment with oxygen-containing plasma is an essential step for the fabrication of devices containing components of polydimethylsiloxane (PDMS). Such oxidative treatment chemically modifies the surface of PDMS allowing it to permanently adhere to glass, quartz, PDMS and other silica-based substrates. Overexposure of PDMS to oxidative gas plasma, however, compromises its adhesiveness. Therefore, regulation of the duration and the conditions of the plasma treatment is crucial for achieving sufficient surface activation without overoxidation. Using a semiquantitative ternary approach, we evaluated the quality of adhesion ( QA) between flat PDMS and glass substrates pretreated with oxygen plasma under a range of different conditions. The quality of adhesion manifested good correlation trends with the surface properties of the pretreated PDMS. Examination of the QA dependence on the treatment duration and on the pressure and the RF power of the plasma revealed a range of oxidative conditions that allowed for permanent adhesion with quantitative yields.     

Creating patterned poly(dimethylsiloxane) surfaces with amoxicillin and poly(ethylene glycol)

This paper reports a simple microwave plasma patterning of poly(dimethylsiloxane) (PDMS) surfaces, which is accomplished by allowing selective surface areas to microwave plasma exposure in the presence of gaseous monomer. When maleic anhydride is used for microwave plasma reaction in the presence of physical barrier on the PDMS substrate, the resulting patterned surfaces with chemically bonded maleic anhydride and carboxylic acid groups are generated. In this particular study we attached amoxicillin via ammonolysis under weak base conditions in the presence of a catalyst as well as poly(ethyleneglycol) (PEG). A combination of internal reflection IR imaging (IRIRI) and atomic force microscopy (AFM) revealed that amoxicillin and PEG can be readily reacted on the microwave plasma patterned PDMS surfaces. Surface areas directly exposed to microwave plasmons exhibit the highest reactivity due to higher content of functional groups. These studies also show that molecular weight of PEG has also significant effect on kinetics of surface reactions.