Surface initiated polymerization from substrates of low initiator density and its applications in biosensors

Surface initiated polymerization (SIP) has become an attractive method for tailoring physical and chemical properties of surfaces for a broad range of applications. Most of those applications relied on the merit of high density coating. In this study, we explored a long overlooked field of SIP: SIP from substrates of low initiator density. We combined ellipsometry with AFM to investigate the effect of initiator density and polymerization time on the morphology of polymer coatings. In addition, we carefully adjusted the nanoscale separation of polymer chains to achieve a balance between nonfouling and immobilization capacities. We further tested the performance of those coatings on various biosensors, such as quartz crystal microbalance, surface plasmon resonance, and protein microarrays. The optimized matrices enhanced the performance of those biosensors. This report shall encourage researchers to explore new frontiers in SIP that go beyond polymer brushes.     

Klebflächenvorbehandlung von Aluminiumoberflächen mit SIP‐Haftvermittler

Surface pretreatment for adhesive bonding of aluminium with adhesive mediator SIP The present contribution describes the influence of different surface pretreatments including adhesive mediator SIP for adhesive bonding of aluminium alloy AlMg4,5Mn0,4. The investigations were performed using two cold hardening two‐components epoxy‐adhesives, one hot hardening one‐component epoxy‐adhesive and one cold hardening two‐components polyurethane‐adhesive. The adhesive bonds with epoxy‐adhesives show after three‐step pretreatment degreasing + corundblasting + SIP coating the highest adhesive strength values whereas adhesive bonds with polyurethane‐adhesive showed a decrease of bond strength as compared with the delivering surface condition.     

Microwave-Assisted Fabrication of Superamphiphobic Surfaces on Aluminum Substrates

The field of superamphiphobic surface fabrication has evolved rapidly in the last decade; however, research on important issues such as sustainability and green chemistry procedures is still scarce. Herein, a simple method of microwave irradiation (MW) to minimize energy consumption during the preparation of superamphiphobic aluminum (Al) surfaces is reported. Al substrates are first etched in diluted HCl solutions to generate a microstructure and then irradiated in a commercial microwave unit for several time intervals, temperatures, and pressures. The surfaces are then coated with different compounds, and the wettability is tested with high and very-low surface tension liquids. Optical profilometry and scanning electron microscopy images show that the density of hierarchical micro-nanostructures increases with MW time, temperature, and pressure. At 170 °C and 7.9 bar, the surfaces present a high density of structures and re-entrant topographies. The obtained coatings display excellent repellence to liquids with surface tensions as low as 27.5 mN m⁻¹. X-ray photoelectron spectroscopy data show the importance of efficient surface functionalization for the production of superamphiphobicity in Al substrates. The results show that MW irradiation of Al substrates can be a green and efficient method for fabricating superamphiphobic surfaces.     

Evaluation of in situ albumin binding surfaces: a study of protein adsorption and platelet adhesion

Surface modification strategies that take advantage of the passivation effects of albumin are important in the development of biomaterial surfaces. In this study, linear peptides (LP1, LP2) and a small chemical ligand (SCL) with albumin binding affinities were grafted onto silane functionalized silicon substrates. Surfaces were characterized with contact angle and ellipsometric measurements, and densities of immobilized ligands were assessed spectroscopically. Ellipsometrically measured thickness correlated with the predicted molecular lengths of grafted moieties. Contact angle analysis indicated that the LP1 and LP2 functionalized surfaces were hydrophilic compared to SCL functionalized and control surfaces. Adsorption of albumin from human serum was evaluated and quantified via specific enzyme-linked immunosorbent assays and 2D gel electrophoresis. The following trend was noted for surface adsorbed albumin: LP1 > LP2 > SCL > C, with LP1 derivatized surfaces having ~2.450 μg/cm² of bound albumin. LP1 derivatized surfaces possessed the least number of adsorbed platelets with rounded platelet morphology when compared to control surface.     

Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings

Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings was carried out. The objectives were to demonstrate that such difficult-to-machine coating surfaces could be machined with commercial machines and tools, and to characterize the surface finish of the machined coatings. The coatings were obtained using two thermal spraying processes: arc spraying and high velocity oxy-fuel spraying. Different machining techniques were tried to optimize the surface finishing of the coatings based on surface finish and time required. Machined samples were then examined using stylus roughness testers. Surface roughness parameters R_a and R_q were measured using various cut-off lengths, sampling lengths, and numbers of sampling and cut-off lengths to characterize the scaling behavior of the surfaces. Diamond turning of WC–Co demonstrated the advantage of high material removal rates, and diamond grinding of WC–Co produced good surface finish with relatively high material removal rates. Precision-machined WC–Co and Alloy-625 surfaces could be identified as self-affine fractals in a statistical sense within the correlation length, i.e. within the length scales studied from 0.08 to 8 mm. The surface roughness heights of the machined surfaces were found to be dependent on the scale of cut-off length as a power law.     

Surface activity of perfluoropolyalkylether <Emphasis Type="Italic">N,N</Emphasis>-diphenylamide (PFPEA)

A functional derivative of perfluoropolyalkylether, perfluoropolyalkylether N,N-diphenylamide (PFPEA) was synthesized and characterized by FT-IR, ¹H and ¹⁹F NMR, and the thermo stability was determined by TG analysis. The surface activity of PFPEA was characterized by the determination of surface tension of organic solvents and the adsorption behavior on the surfaces of solids such as Fe, Al, Cu plates. PFPEA reduced the surface tension of organic solvents greatly such as benzene, toluene, hexane, and cyclohexane. PFPEA was adsorbed on surfaces of solids to form molecular thin films through the end groups. Surface properties of thin films of PFPEA formed by adsorption in organic solutions were characterized using contact angle measurements and X-ray Photoelectron Spectrum (XPS) analysis. The anti-wear performances of adsorbed thin films of PFPEA were determined on a four-ball tribo-tester under the lubrication of liquid lubricants. Films preadsorbed on the substrate surfaces could improve the anti-wear properties of liquid lubricants.     

Adhesive interactions of geckos with wet and dry fluoropolymer substrates

Fluorinated substrates like Teflon^® (poly(tetrafluoroethylene); PTFE) are well known for their role in creating non-stick surfaces. We showed previously that even geckos, which can stick to most surfaces under a wide variety of conditions, slip on PTFE. Surprisingly, however, geckos can stick reasonably well to PTFE if it is wet. In an effort to explain this effect, we have turned our attention to the role of substrate surface energy and roughness when shear adhesion occurs in media other than air. In this study, we removed the roughness component inherent to commercially available PTFE and tested geckos on relatively smooth wet and dry fluoropolymer substrates. We found that roughness had very little effect on shear adhesion in air or in water and that the level of fluorination was most important for shear adhesion, particularly in air. Surface energy calculations of the two fluorinated substrates and one control substrate using the Tabor–Winterton approximation and the Young–Dupré equation were used to determine the interfacial energy of the substrates. Using these interfacial energies we estimated the ratio of wet and dry normal adhesion for geckos clinging to the three substrates. Consistent with the results for rough PTFE, our predictions show a qualitative trend in shear adhesion based on fluorination, and the quantitative experimental differences highlight the unusually low shear adhesion of geckos on dry smooth fluorinated substrates, which is not captured by surface energy calculations. Our work has implications for bioinspired design of synthetics that can preferentially stick in water but not in air.     

3D Printing of Bioinspired Liquid Superrepellent Structures

Bioinspired re‐entrant structures have been proved to be effective in achieving liquid superrepellence (including anti‐penetration, anti‐adhesion, and anti‐spreading). However, except for a few reports relying on isotropic etching of silicon wafers, most fluorination‐dependent surfaces are still unable to repel liquids with extreme low surface energy (i.e., γ < 15 mN m^?1), especially those fluorinated solvents. Herein, triply re‐entrant structures, possessing superrepellence to water (with surface tension γ of 72.8 mN m^?1) and various organic liquids (γ = 12.0–27.1 mN m^?1), are fabricated via two‐photon polymerization based 3D printing technology. Such structures can be constructed both on rigid and flexible substrates, and the liquid superrepellent properties can be kept even after oxygen plasma treatment. Based on the prepared triply re‐entrant structures, micro open capillaries are constructed on them to realize directional liquid spreading, which may be applied in microfluidic platforms and lab‐on‐a‐chip applications. The fabricated arrays can also find potential applications in electronic devices, gas sensors, microchemical/physical reactors, high‐throughput biological sensors, and optical displays.     

Hydrophobic treatment enabling analysis of wettable surfaces using a liquid microjunction surface sampling probe/electrospray ionization-mass spectrometry system

An aerosol application procedure involving one or more commercially available silicone-based products was developed to create hydrophobic surfaces that enable analysis of otherwise wettable, absorbent surfaces using a liquid microjunction surface sampling probe/electrospray ionization mass spectrometry system. The treatment process resulted in a hydrophobic surface that enabled formation of the requisite probe-to-surface liquid microjunction for sampling and allowed efficient extraction of the analytes from the surface, but did not contribute significant chemical background in the mass spectra. The utility of this treatment process was demonstrated with the treatment of wettable high-performance thin layer chromatography plates, post-plate development, and their subsequent analysis with the sampling probe. The surface treatment process for different surface types was described and explained and the effectiveness of the treatment and subsequent analysis was illustrated using alkaloids from goldenseal (Hydrastis canadensis) root separated on a normal phase silica gel 60 F(254S) plate and peptides from protein tryptic digests separated on a ProteoChrom HPTLC Silica gel 60 F(254S) plate and a ProteoChrom HPTLC Cellulose sheet. This simple surface treatment process significantly expands the analytical surfaces that can be analyzed with the liquid microjunction surface sampling probe, and therefore, also expands the analytical utility of this liquid extraction based surface sampling approach.     

Influence of plastic deformation in flexible pad laser shock forming – experimental and numerical analysis

Flexible Pad Laser Shock Forming (FPLSF) is a new microforming process using laser-induced shock pressure and a hyperelastic flexible pad to induce high strain-rate (~10⁵ s^?1) plastic deformation on metallic foils to produce 3D microcraters. This paper studies the effect of two significant process parameters of FPLSF, flexible pad material and its thickness, on the deformation characteristics of the metal foils using experiments and finite element analysis. A finite element model is developed to simulate the FPLSF process. The stress-strain distribution across the foil and the flexible pad at different process stages of FPLSF are studied using FE analysis. Flexible pad materials including silicone rubber, polyurethane rubber, and natural rubber with thicknesses ranging between 300 μm and 3000 μm have been investigated in detail. Experimental results highlight that both the hardness and thickness of the flexible pad significantly influence the deformed crater geometry, thickness distribution across the formed crater and surface hardness at the crater surfaces. The experimental results are correlated with the stress-strain distributions from finite element analysis to study the underlying behaviors.     

Removal of surface contamination and self-assembled monolayers (SAMs) from silver (Ag) nanorod substrates by plasma cleaning with argon

Surface contamination of surface-enhanced Raman (SERS)-active metallic substrates has been a limitation to the utility of SERS as an analytical technique, potentially affecting surface coverage, spectral reproducibility, and analytical limits of detection. We have developed a simple and versatile cleaning method for SERS-active Ag nanorod arrays that consists of a short (4 min) exposure of the substrate to an Ar(+) plasma in a low-pressure environment. The findings presented here demonstrate that this cleaning procedure essentially eliminates organic background contamination. This procedure works equally well for self-assembled monolayers of thiolates that strongly adsorb onto Au and Ag surfaces. For SERS-active surfaces composed of arrays of Ag nanorods prepared by oblique-angle vapor deposition, we investigated the (1) Raman band intensities, (2) nanorod morphology via scanning electron microscopy, and (3) surface hydrophobicity via static contact angle measurements, as a function of exposure time of the Ag nanorods to the Ar(+) plasma. Short (4 min) exposure to Ar(+) plasma eliminated background contamination but decreased the observed SERS intensity for re-adsorbed analytes by approximately a factor of 2 while leaving the nanorod morphology essentially unchanged. Prolonged exposure to Ar(+) plasma (>10 min) resulted in substantial morphological changes of the Ag nanorod lattice and led to a decrease in the observed SERS intensities by a factor of 10. The results presented here suggest that Ar(+) plasma cleaning is an efficient process for removing carbonaceous and organic contamination as well as thiolate monolayers from SERS-active Ag surfaces, as long as the plasma conditions and exposure times are carefully monitored.     

NURBS曲面的过渡曲面生成

曲面过渡是几何造型的关键技术之一，本文提出的ＮＵＲＢＳ曲面的过渡曲面生成方法，能够处理曲面内具有不同连续性的情况，解决了ＮＵＲＢＳ曲面的等半径，变半径过渡及三面过渡问题，并在超人ＣＡＤ／ＣＡＭ系统中实现。     

Scanning and surface alignment considerations in chemical imaging with desorption electrospray mass spectrometry

The effects of surface scanning mode (raster vs unidirectional scanning) and the constancy of spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances on chemical image quality using desorption electrospray ionization mass spectrometry were investigated. Unidirectional scanning was found to provide a spatially and a quantitatively more precise chemical image of the surface as compared to raster scanning. Maintaining constant spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances during an imaging experiment was found to also be critical. An automation process was implemented using a custom image analysis software (HandsFree Surface Analysis) to keep these distances constant during the surface sampling experiment. Improved chemical image quality afforded through this software control was illustrated by imaging printed objects on normal copy paper.     

Solid‐Supported Biomolecules on Modified Silica Surfaces—A Tool for Fast Physicochemical Characterization and High‐Throughput Screening

Biofunctionalization for a wide variety of applications can be achieved by coating silica surfaces with biomolecules such as lipids or proteins. However, specific surface optimization of the inorganic SiO₂ is necessary to achieve biocompatible surfaces. Surface shielded porous silica beads can be non‐covalently coated with a single lipid bilayer. The lipids retain their fluidity in this handy solid‐supported system, perfectly mimicking the soft‐surface properties of cellular membranes. A supramolecular architecture can also be used for functional immobilization of membrane proteins: An artificial cytosolic compartment can be created with the aid of polymers; coating by lipid membranes and integration of membrane proteins results in a solid‐supported biofunctional cellular surface. Another surface modification enables a direct immobilization of human serum albumin (HSA) molecules onto silica surfaces. The HSA on this otherwise passivated surface provides a convenient material for the investigation of unspecific protein binding of pharmaceuticals on a high‐throughput scale.     

Comparative investigation of the surface properties of commercial titanium dental implants. Part I: chemical composition

The surfaces of five commercially available titanium implants (Brånemark Nobel Biocare, 3i ICE, 3i OSSEOTITE, ITI-TPS, and ITI-SLA) were compared by scanning electron microscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy. All five implant types were screw-shaped and fabricated from commercially pure (cp) titanium, but their surface properties differed both as regards surface morphology and surface chemical composition. The macro- and microstructure of the implant surfaces were investigated by scanning electron microscopy. The surfaces chemical composition was determined using the surface-sensitive analytical techniques of X-ray photoelectron spectroscopy and time-of-flight secondary ion spectrometry. Surface topographies were found to reflect the type of mechanical/chemical fabrication procedures applied by the manufacturers. The titanium oxide (passive) layer thickness was similar (5–6 nm) and typical for oxide films grown at or near room temperature. A variety of elements and chemical compounds not related to the metal composition were found on some implant types. They ranged from inorganic material such as sodium chloride to specific organic compounds believed to be due to contamination during fabrication or storage. The experimental findings are believed to make a contribution to a better understanding of the interplay between industrial fabrication procedure and physico-chemical implant surface properties.     

Superwetting Surfaces under Different Media: Effects of Surface Topography on Wettability

Superwetting surfaces in air, such as superhydrophobic and superoleophobic surfaces that are governed by surface chemical compositions and surface topographies, are one of the most extensively studied topics in this field. However, it is not well‐understood how surface topographies affect the behaviors of immiscible liquids and gases under other kinds of media, although it is significant in diverse fields. The main aim of this work is to systematically investigate the wetting behaviors of liquids (water and oil) and gas (air) on silicon surfaces with different topographies (i.e., smooth, micro, nano, and micro‐/nanostructures) under various media (i.e., air, water, and oil). The contact angles, as well as contact‐angle hysteresis, sliding angles, and adhesive forces, were utilized to evaluate the wettability of these surfaces. As a result, the microstructured surfaces typically exhibit high contact‐angle hysteresis, high sliding angles, and high adhesive forces, whereas the micro‐/nanostructured surfaces display low contact‐angle hysteresis, low sliding angles, and low adhesive forces, even if they have high (>150°) and similar contact angles. Furthermore, when transferring the same surface from one kind of medium to another, different superwetting states can be reversibly switched.     

In vivo synthesis of calcium oxalate whiskers on CoCrMo alloy surfaces via biomineralization

Surface treatments using bio-technology are valuable and fascinating in the sense that such treatments are natural and yield good biocompatibility. Calcium oxalate whiskers for biomedical applications were successfully synthesized on the CoCrMo alloy surfaces implanted in Aloe leaves which consist of many active bio-chemical elements. The effect of surface wettability and surface morphology on the formation of whiskers was investigated using four differently treated CoCrMo surfaces: (i) smoothly polished surface, (ii) electrochemical etched surface, (ii) textured surface with dimples, and (iv) parallel orientated-grooved surface. Results showed that the formed whiskers had a length ranging between 100 μm and 600 μm, and a diameter in the range of 2 μm to 5 μm. Electrochemically etched surfaces had better wettability and were favorably for growing whiskers. Surface morphology with (i) dimple textures or (ii) parallel grooves facilitated the effective control of the size and amount of the grown whiskers.     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

The paper is concerned with the surface chemistry of several different carbon fibres subjected to various surface treatments. The microstructure and nanostructures of these fibres were investigated in the Part I of this series of papers. For analysis of the surface chemistry of the fibres, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) were employed; the first method was used for identification and semi-quantitative determination of functional surface groups, while the second method was used for a quantitative determination of these groups. The possible interactions of the various carbon-fibre surfaces due to different surface treatments (and therefore to different functional groups) were analysed by wetting studies using the Wilhelmy technique and aqueous solutions of different pH values as test liquids. By variation of the pH value of the test liquids, the distinct acid-base complexes that formed with the functional groups were identified. The same test liquids were used for characterization of the surface chemistry of the high-temperature thermoplastics (polycarbonate and polyethersulphone) used as matrix materials in the fabrication of the composites in this study. Acid-base interactions at the carbon-fibre surfaces are mainly determined by carboxylic groups of different acidity. The concentration of these groups as determined by desorption of carbon dioxide up to 500 °C is shown to be directly proportional to the measured work of adhesion of each group.     

Observation and analysis of the detachment frequency of coalesced bubbles in pool boiling liquid nitrogen

The detachment frequency of coalesced bubbles is one of the important parameters in the boiling heat transfer model at high heat flux. Although some researches on detachment frequency of coalesced bubbles have been done for common liquids, the work on cryogenic liquids is relatively insufficient. A visual experimental apparatus was built for observing the boiling in liquid nitrogen. The growth process of coalesced bubbles was recorded by a high-speed camera, emphasizing on the detachment frequency of coalesced bubbles from the circular, horizontal heating surfaces. The effects of the heating surface material, the surface diameter and the heat flux on the detachment frequency were analyzed. The available empirical correlations from common liquids are compared with our experimental data to check their applicability in liquid nitrogen, where the detachment frequency is 13.47 s⁻¹.     

Surface characterization of GaN and AlGaN layers grown by MOVPE

Surface properties of GaN and Al_0.17Ga_0.83N materials grown by metal organic vapor phase epitaxy (MOVPE) were systematically investigated by X-ray photoelectron spectroscopy (XPS). Air-exposed samples showed highly non-stoichiometric surfaces, which included a large amount of natural oxides. Deposition of Al on the air-exposed GaN surface caused interfacial reactions, resulting in the formation of oxide layers including Al₂O₃ and Ga oxide at the interface. A natural oxide layer of AlGaN surface possessed a complicated composition distribution in depth where the Al-oxide component was dominant on the topmost layer. Such natural oxide layers were found to be removed from GaN and AlGaN surfaces after the treatment in an NH₄OH solution at 50°C for 10 min, resulting in oxide-free and well-ordered surfaces.