Contact Atomic Force Microscopy Research Articles

Detection of Gadolinium with an Impedimetric Platform Based on Gold Electrodes Functionalized by 2-Methylpyridine-Substituted Cyclam.

Gadolinium is extensively used in pharmaceuticals and is very toxic, so its sensitive detection is mandatory. This work presents the elaboration of a gadolinium chemical sensor based on 2-methylpyridine-substituted cyclam thin films, deposited on gold electrodes, using electrochemical impedance spectroscopy (EIS). The 2-methylpyridine-substituted cyclam (bis-N-MPyC) was synthesized in three steps, including the protection of cyclam by the formation of its CH2-bridged aminal derivative; the product was characterized by liquid 1H and 13C NMR spectroscopy. Spin-coated thin films of bis-N-MPyC on gold wafers were characterized by means of infrared spectroscopy in ATR (Attenuated Total Reflectance) mode, contact angle measurements and atomic force microscopy. The impedimetric chemical sensor was studied in the presence of increasing concentrations of lanthanides (Gd3+, Eu3+, Tb3+, Dy3+). Nyquist plots were fitted with an equivalent electrical circuit including two RC circuits in series corresponding to the bis-N-MPyC film and its interface with the electrolyte. The main parameter that varies with gadolinium concentration is the resistance of the film/electrolyte interface (Rp), correlated to the rate of exchange between the proton and the lanthanide ion. Based on this parameter, the detection limit obtained is 35 pM. The bis-N-MPyC modified gold electrode was tested for the detection of gadolinium in spiked diluted negative urine control samples.

Effect of surface roughness and temperature on stainless steel - Whey protein interfacial interactions under pasteurisation conditions

The effects of the surface characteristics of 316L stainless steel (SS316L), including chemical composition before and after foulant deposition, surface roughness, and wall temperature, on both the liquid-solid and the solid-solid interfacial interactions have been investigated using contact angle measurements and atomic force microscopy respectively. Wettability of the metal surface was favoured by increased surface roughness (in the range-limited for food contact applications) and wall temperature (within the temperature range used for pasteurisation). A fine surface finish (i.e. mirror) could be an effective intervention to reduce liquid adhesion and the subsequent foulant deposition, especially under thermal treatment. The surface free energy (SFE) of SS316L and its polar and disperse components remained constant from ambient to pasteurisation temperatures (<80°C). However, as fouling develops, the surface free energy evolved: upon foulant deposition, SFE decreased. An increased polarity (3.4% from 25 to 80°C) of the fouled surface could be related to the exposure the hydrophobic core of reversibly adsorbed β-Lactoglobulin toward the foulant-air interface. Both surface adhesion and Young's modulus at sub-micron spatial resolution confirmed that the packing within the foulant and molecular orientation on the foulant surface were affected by the temperature of the underlying substrate. Temperature also affected the wetting behaviour of cleaning solutions on surface foulant; as the surface temperature increased from 25°C to 75°C, the contact angle on WPC increased, suggesting an enhanced surface hydrophobicity. Overall, this work highlights the importance of surface parameters on governing the interfacial interactions that are competing for the control of the complex fouling phenomena.

Mg:TiO2 alloy thin films based MOS capacitors grown on GaAs substrates

Electron beam evaporation technique is employed to synthesise TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 thin films (TFs) grown on (100) n-type GaAs substrates. Field emission gun-scanning electron microscope (FEG-SEM) results show that the TFs have a thickness of ~225 nm. The non- contact atomic force microscopy (NC-AFM) images shows the pore volume of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 TFs enhanced gradually. UV-Vis absorption measurements are performed on the samples to determine the main bandgap and defect level transition of the material. A unique modified Urbach theoretical model has been introduced to simulate the experimental absorption spectrum. The main bandgap energy of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 samples are calculated to be ~3.45 eV, 3.85 eV and 4.30 eV respectively. A gradual enhancement in main bandgap transition probability and decrease in defect level transition of the material has been observed with enhanced incorporation of Mg into the TiO2 host material. X-ray diffraction (XRD) is performed, which shows a continuous change in lattice constant of TiO2 with Mg. Current (I)-voltage (V) characteristics of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 Schottky devices revealed that the leakage current at −1 V was 1.28 × 10−6 A, 1.46 × 10−9 A and 2.44 × 10−10 A respectively. Capacitance (C)–voltage (V) measurements are performed on the devices at different frequencies. A theoretical simulation has been adopted by amending the delta depletion model at 1 MHz. The dielectric constant and the flat band voltage of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 devices are found to be 100, 120 and 160 and 16.1 V, 14.7 V and 9.7 V respectively. Hill-Coleman’s method shows a gradual enhancement of the density of interface states (Dit) with Mg concentration. The calculated Dit value of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 TF devices are ~6.16 × 1010 eV−1 cm−2, 6.44 × 1010 eV−1 cm−2 and 1.11 × 1011 eV−1 cm−2 respectively. The observed C-V hysteresis confirms an enhancement in the charge retention into the film with increasing Mg concentration, which in turn improves the memory window (MW) from ~0.36 V (at±7 V) to ~0.67 V (at±7 V) and ~0.87 V (at±10 V) to ~1.0 V (at±10 V) with sweeping voltage.

Surface Modification of PDMS-Based Microfluidic Devices with Collagen Using Polydopamine as a Spacer to Enhance Primary Human Bronchial Epithelial Cell Adhesion.

Polydimethylsiloxane (PDMS) is a silicone-based synthetic material used in various biomedical applications due to its properties, including transparency, flexibility, permeability to gases, and ease of use. Though PDMS facilitates and assists the fabrication of complicated geometries at micro- and nano-scales, it does not optimally interact with cells for adherence and proliferation. Various strategies have been proposed to render PDMS to enhance cell attachment. The majority of these surface modification techniques have been offered for a static cell culture system. However, dynamic cell culture systems such as organ-on-a-chip devices are demanding platforms that recapitulate a living tissue microenvironment’s complexity. In organ-on-a-chip platforms, PDMS surfaces are usually coated by extracellular matrix (ECM) proteins, which occur as a result of a physical and weak bonding between PDMS and ECM proteins, and this binding can be degraded when it is exposed to shear stresses. This work reports static and dynamic coating methods to covalently bind collagen within a PDMS-based microfluidic device using polydopamine (PDA). These coating methods were evaluated using water contact angle measurement and atomic force microscopy (AFM) to optimize coating conditions. The biocompatibility of collagen-coated PDMS devices was assessed by culturing primary human bronchial epithelial cells (HBECs) in microfluidic devices. It was shown that both PDA coating methods could be used to bind collagen, thereby improving cell adhesion (approximately three times higher) without showing any discernible difference in cell attachment between these two methods. These results suggested that such a surface modification can help coat extracellular matrix protein onto PDMS-based microfluidic devices.

Nanomechanical characterisation of a water-repelling terpolymer coating of cellulosic fibres

Polymer coatings on cellulosic fibres are widely used to enhance the natural fibre properties by improving, for example, the hydrophobicity and wet strength. Here, we investigate the effects of a terpolymer P(S-co-MABP-co-PyMA) coating on cotton linters and eucalyptus fibres to improve the resistance of cellulose fibres against wetness. Coated and uncoated fibres were characterised by using scanning electron microscopy, contact angle measurements, Raman spectroscopy and atomic force microscopy with the objective of correlating macroscopic properties such as the hydrophobicity of the fleece with microscopic properties such as the coating distribution and local nanomechanics. The scanning electron and fluorescence microscopy results revealed the distribution of the coating on the paper fleeces and fibres. Contact angle measurements proved the hydrophobic character of the coated fleece, which was also confirmed by Raman spectroscopy measurements that investigated the water uptake in single fibres. The water uptake also induced a change in the local mechanical properties, as measured by atomic force microscopy. These results verify the basic functionality of the hydrophobic coating on fibres and paper fleeces but call into question the homogeneity of the coating.Graphic abstract

Mechanical characterization of P2 bacteriophage by using Young’s modulus measurements

The bacteriophage P2 capsids have been characterized by transmission electron microscopy and atomic force microscopy (AFM). Studies have been carried out on fully filled and 2/3 filled capsids containing dsDNA genomes. In order to get the quantitative information of the capsid, a nanoindentation technique depending on the tip-shape and an effective spring constant technique with a homogeneous capsid shell model were adopted. The contact region of the AFM contact force curve in an approach mode has been used for the calculation of Young’s moduli as well as the internal pressures of the capsids. By using the continuum theory of elasticity of thin homogeneous capsid shells, Young’s moduli of fully filled and 2/3 filled phage capsids are measured to be 1.17 ± 0.10 GPa and 0.87 ± 0.10 GPa, respectively. These values are close to other reported results. Analysis of the force curves also presented that a fully filled capsid reveals a higher internal pressure than that of a 2/3 filled capsid.

Facile Li-Al layered double hydroxide films on Al alloy for enhanced hydrophobicity, anti-biofouling and anti-corrosion performance

In this work, lithium (Li)-aluminum (Al) layered double hydroxide (LDH) films modified by 4-amino-2-((hydrazine methylene) amino)-4-oxobutanoic acid (denoted as AOA acid) and/or 1H,1H,2H,2H-perfluorooctyltriethoxysilane were prepared on 6N01 Al alloy by a facile, in-situ growth method with enhanced hydrophobicity, anti-biofouling and anti-corrosion performance. The preparation is low energy consumptive and environment friendly, relying on self-assembly at ambient temperature. The structure, molecular weight and functional groups of the synthesized AOA acid were characterized by NMR spectrometer, ESI-MS spectrometer and Fourier transform infrared (FT-IR) spectroscopy. And the compositions, structure and morphology of the films were characterized by Fourier transform infrared (FT-IR) spectroscopy, glancing-angle X-ray diffraction (GA-XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and energy-dispersive x-ray spectrum (EDS). Water contact angle measurements (CA) and atomic force microscopy (AFM) characterization show that the films possess a micro/nanostructure with an improved hydrophobicity. Immersion test, neutral salt tests (NSS) and electrochemical impedance spectroscopy (EIS) conducted in 3.5 wt.% NaCl solutions demonstrate the improved corrosion resistance of the films over bare Al alloy. Meanwhile, the films also possess an excellent anti-bacterial property to Escherichia coli, Bacillus subtilis and sulfate-reducing bacteria.

Atomic force microscopy for nanoscale mechanical property characterization

Over the past several decades, atomic force microscopy (AFM) has advanced from a technique used primarily for surface topography imaging to one capable of characterizing a range of chemical, mechanical, electrical, and magnetic material properties with subnanometer resolution. In this review, we focus on AFM as a nanoscale mechanical property characterization tool and examine various AFM contact and intermittent contact modes that add mechanical contrast to an imaged surface. Through detailed analysis of the tip-sample contact mechanics, this contrast can be converted into quantitative measurements of various nanomechanical properties including elastic modulus, shear modulus, wear rate, adhesion, and viscoelasticity. Different AFM modes that provide such measurements are compared and contrasted in this work on a wide range of materials including ceramics, metals, semiconductors, polymers, and biomaterials. In the last few years, considerable improvements have been made in terms of fast imaging capabilities, tip preservation, and quantitative mechanics for multifrequency measurements as well as well-known AFM modes like amplitude modulation and peak-force tapping. In line with these developments, a major highlight of this review is the discussion of the operation and capabilities of one such mode, namely, intermittent contact resonance AFM (ICR-AFM). The applications of ICR-AFM to nanoscale surface and subsurface quantitative mechanical characterizations are reviewed with specific examples provided for thin polymeric films and patterned nanostructures of organosilicate dielectric materials. The combination of AFM-based mechanical characterization with AFM-based chemical spectroscopy to allow nanoscale structure-property characterization is also discussed and demonstrated for the analysis of low-k dielectric/copper nanoelectronic interconnect structures and further highlights synergistic advances in the AFM field.

Effect of the feeding mode of cross-linker and microcapsule on the corrosion resistance and hydrophobicity of composite coatings

The interface combination of anti-corrosive materials and polymer matrix has a significant effect on the overall performance of the composite coating. However, past research has focused on blending anti-corrosive materials to improve the performance of the polymer matrix. Herein, we proposed a layer-by-layer spray-coating process to further enhance the reinforcing effect of anti-corrosive materials on the polymer matrix by changing their feeding modes. In this paper, taking waterborne polyacrylate (WPA) as an example, two kinds of reinforcement materials commonly used to improve the corrosion resistance of polymer matrix were introduced into the coating system and then applied to the tinplate: cross-linker and microcapsule. Firstly, five types of WPA composite coating systems were designed according to the feeding mode of aziridine cross-linker and the position of benzotriazole@zinc oxide microcapsules (BTA@ZnO MCs). Electrochemical impedance spectroscopy (EIS) and electrical equivalent circuits were used to evaluate the corrosion resistance of these composite coating systems and analyze their electrochemical processes. By spraying the mixture of WPA and aziridine crosslinker as the bottom layer and BTA@ZnO MCs as the top layer, the resulting composite coating exhibited higher corrosion resistance and hydrophobic properties. Scanning electron microscope (SEM) and contact angle tests indicated that the feeding mode of aziridine cross-linker and the position of BTA@ZnO MCs played important roles in the compactness and hydrophobicity of the composite coating. Subsequently, the effects of the amount of aziridine cross-linker and BTA@ZnO MCs on the corrosion resistance and physical properties of the composite coating were further analyzed by EIS, water absorption test, contact angle test and atomic force microscopy (AFM). The significant improvement in the corrosion resistance of this composite coating was mainly attributed to the synergistic effect of highly cross-linked network structure and superhydrophobic surface.

Influence of pH on Acidic Oil–Brine–Carbonate Adhesion Using Atomic Force Microscopy

Wettability alteration seems to be the main physicochemical process during low salinity water injection in carbonate formations. A pH increase due to calcite dissolution during low salinity water injection may affect oil–brine–rock interaction and thereby wettability. However, far too little attention has been paid to quantifying the impact of such an pH increase on acidic oil–carbonate adhesion. Therefore, we measured contact angles between acidic oil (−COOH) and calcite crystal in the presence of 10 000 ppm NaCl solutions at different pHs (6.5, 9.5 and 11) at ambient conditions. Furthermore, we used atomic force microscopy (AFM) to measure the adhesion force between acidic oil groups (−COOH) and calcite substrate at different pHs (9.5 and 11) at similar conditions of the contact angle experiments. Moreover, to confirm the contact angle and AFM results, we measured the zeta potential of acidic oil−brine and calcite−brine interfaces at the same condition and calculated the thermodynamic isotherm disjoining pressure. Our results show that the contact angle reduces from 134 to 95° as the pH increases from 6.5 to 11, increasing hydrophilicity. Adhesion force measurements show that increasing pH reduces the adhesion force between the acidic oil and carbonate in line with contact angle results. Zeta potential results show that increasing the pH increases the negativity of the zeta potential of acidic oil–brine and calcite–brine interfaces, implying the increase of the electrical double layer force. Furthermore, the total disjoining pressure isotherm becomes less negative with increasing pH, implying an increase of hydrophilicity. Taken together, our results confirm that a local pH increase due to calcite dissolution during low salinity water injection would prevail in the wettability alteration process in particular for high acidic oil bearing carbonate reservoirs.

Robust three‐dimensionally printed polypropylene/highly sulfonated polysulfone composites for potential applications in fuel cells

Advanced ion-conducting composites were prepared by ionomer synthesis, fused deposition modeling (FDM) 3D-printing, surface modification, and pore-filling. The cost-effective, mechanically robust, and inert microporous substrates of polypropylene were made by FDM printing. Three infill contents of 30, 50, and 70 vol% of polypropylene were designed. A synthesized highly sulfonated hydroquinone-based polysulfone, with 80% degree of sulfonation (DS), was used as the pore material. Nucleophilic aromatic substitution on difluorodiphenyl sulfone was used to synthesize the highly sulfonated ionomer. Pore-filling of the designed printed substrate was done via 10 w/v% of the ionomer solution. Oxygen plasma treatment was applied to enhance the compatibility of the substrate and the pore material's interfaces. Modification of porous substrate was confirmed by alteration of surface polar characteristics and roughness from contact angle measurements and atomic force microscopy, respectively. Confinement of highly sulfonated ionomer by the robust structure resulted in the preparation of electrolyte with controlled water uptake, no in-plane swelling, high conductivity (up to 0.417 S/cm at 60°C under 100% relative humidity), and current density of about 836 mA.cm−2 at 60°C under 100% relative humidity. Regarding the presence of commodity polypropylene in the structure, the performance was good, compared to commercial Nafion membrane, with a cell current density of about 1120 mA.cm−2.

Epitaxial Nanostructured α-Quartz Films on Silicon: From the Material to New Devices.

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of α-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 °C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO2 between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever's dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 µm large and 100 µm long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 µm, respectively) epitaxially grown on a 2 µm thick Si device layer. Themeasuredresonance frequency was267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Hydrophobic behavior of fluorite surface in strongly alkaline solution and its application in flotation

Normally fluorite was collected by fatty acid collectors at pH 5–11, rendering the surface to be hydrophobic. In this study, we found that fluorite surfaces are naturally hydrophobic at high pH without any surfactant, which is beneficial for the selective flotation separation of fluorite from calcite. In a flotation test, fluorite recovery showed a decreasing trend at alkalescent pH but increased at high pH. Sum-frequency generation spectroscopy spectrum confirmed that the orientation and hydrogen bonding structure of the water molecules are dramatically changed at fluorite/water interface. Moreover, a new signal peak, wavenumber of 3657 cm−1, appeared under strongly alkaline conditions; this peak is normally attributed to free OH stretching region and indicates a hydrophobic surface. Meanwhile, the results of contact angle and atomic force microscopy measurements show that the hydrophobicity obviously increases at pH 13. Therefore, the surface structure of fluorite must undergo some significant changes, which will play an important role in the flotation of fluorite.

Effect of Pre-treatment on Roughness and Hydrophobicity of Electro-Etched Steel with Improved Corrosion Resistance

A hydrophobic steel surface was created by a simple electro-etching technique using a cobalt sulfate bath. The effect of surface pre-treatment on the hydrophobicity and surface roughness was investigated. The wettability and roughness of the surface were determined by water contact angle (WCA) and atomic force microscopy (AFM), respectively. Accordingly, the sample abraded with 800 grit sandpaper followed by electro-etching process was selected as the optimum sample with the highest roughness and WCA (Sa = 28.4 nm, Ra = 35.4 nm, and WCA = 144 ± 1.6°, respectively). The morphology and cross-sectional images of the hydrophobic surface were investigated using field-emission scanning electron microscopy (FESEM). FESEM images showed a micro/nanostructured surface. The resulted hydrophobicity was attributed to the high roughness and overhanging structure obtained through this method. Furthermore, by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the corrosion behavior of the samples was investigated. It was revealed that the surface hydrophobicity improved the corrosion resistance by increasing the polarization resistance (from 726 to 1598 Ω cm2) and decreasing the corrosion current density (from 0.025 to 0.012 mA cm−2). The simplicity of creating a hydrophobic surface with the improved corrosion behavior, the availability, and the low cost of the materials used to develop this approach makes it a proper candidate for large-scale and industrial applications.

Characterizing liver sinusoidal endothelial cell fenestrae on soft substrates upon AFM imaging and deep learning

BackgroundLiver sinusoidal endothelial cells (LSECs) display unique fenestrated morphology. Alterations in the size and number of fenestrae play a crucial role in the progression of various liver diseases. While their features have been visualized using atomic force microscopy (AFM), the in situ imaging methods and off-line analyses are further required for fenestra quantification. MethodsPrimary mouse LSECs were cultured on a collagen-I-coated culture dish, or a polydimethylsiloxane (PDMS) or polyacrylamide (PA) hydrogel substrate. An AFM contact mode was applied to visualize fenestrae on individual fixed LSECs. Collected images were analyzed using an in-house developed image recognition program based on fully convolutional networks (FCN). ResultsKey scanning parameters were first optimized for visualizing the fenestrae on LSECs on culture dish, which was also applicable for the LSECs cultured on various hydrogels. The intermediate-magnification morphology images of LSECs were used for developing the FCN-based, fenestra recognition program. This program enabled us to recognize the vast majority of fenestrae from AFM images after twice trainings at a typical accuracy of 81.6% on soft substrate and also quantify the statistics of porosity, number of fenestrae and distribution of fenestra diameter. ConclusionsCombining AFM imaging with FCN training is able to quantify the morphological distributions of LSEC fenestrae on various substrates. SignificanceAFM images acquired and analyzed here provided the global information of surface ultramicroscopic structures over an entire cell, which is fundamental in understanding their regulatory mechanisms and pathophysiological relevance in fenestra-like evolution of individual cells on stiffness-varied substrates.

Near-zero contact force atomic force microscopy investigations using active electromagnetic cantilevers

Atomic force microscopy (AFM) belongs to the high resolution and high sensitivity surface imaging technologies. In this method force interactions between the tip and the surface are observed to characterize sample properties. In the so-called contact AFM (C AFM) mode the tip is brought into continuous contact with the sample. Significant progress in the AFM technology can be obtained, when the so-called active cantilever technology is implemented in the surface measurements. The built-in deflection actuator enables very precise excitation of the cantilever. Moreover, as the mass of the beam is very small the static beam displacement can be controlled in the wide frequency range. In the experiments, which we describe in this article, we applied the so called active electromagnetic cantilevers. They integrate a conductive loop which, when immersed in the magnetic field and biased with electric current, acts as an electromagnetic deflection actuator. The induced and precisely estimated Lorentz force, which is a function of bias current, cantilever geometry and magnetic field makes the cantilever deflect. Moreover, the probe stiffness can be calibrated with lower uncertainty as in the case of standard thermomechanical analysis. NZ AFM technology required application of a novel control algorithm, called PredPID, in which the cantilever bending caused by a proportional-integral-derivative (PID) block maintaining the constant load force was predicted.

Improvement on UHMWPE and PMMA Surface Flashover Under Atmospheric Pressure Using PIII Processing

Polymers are plastic materials used as insulators in power supplies, pulsers, transformers, etc., because of their low cost and excellent insulating properties. However, in several applications, the insulating performance of these materials is limited by the surface flashover instead of the dielectric bulk breakdown (BD). On the other hand, many works have demonstrated that the material hydrophobicity has a huge effect on the increase of resistance to surface flashover in polymers. In this article, to change this material property, the plasma immersion ion implantation (PIII) technique has been used for the treatment of sample surfaces of two important polymers: ultrahigh molecular weight polyethylene (UHMWPE) and poly-methyl-methacrylate (PMMA) used in medical and industrial applications, respectively. By means of the PIII treatment, it was shown that the surface BD voltage of such polymers has increased, improving the resistance to surface flashover. Contact angle diagnostic and atomic force microscopy (AFM) were measured, respectively, for the surface hydrophobicity and roughness to correlate with the increase of the surface BD voltage. Moreover, a special BD testing pulser is employed to assess the polymer resistance to surface flashover by measuring the corresponding BD voltage under atmospheric pressure.

Effect of plasma carrier gas on the moisture barrier properties of plasma-enhanced chemical vapor deposited (PECVD) polyorganosiloxane thin film

A polyorganosiloxane thin film was deposited on an optically transparent poly(ethylene 2,6-naphthalate) (PEN) film using plasma-enhanced chemical vapor deposition (PECVD) at room temperature to improve the moisture barrier property of the PEN film. In the PECVD process, hexamethyldisiloxane (HMDSO) was used as the monomer. Argon or oxygen and their mixture gases were used as the plasma carrier gas. Poly(HMDSO) thin film was successfully deposited through plasma-induced radical polymerization reaction on the surface of PEN film. It was observed that the mixture ratio of argon-oxygen carrier gas significantly affected the surface and the moisture barrier properties of the resulting poly(HMDSO) film. Chemical structures of the poly(HMDSO) were confirmed using FT-IR analysis. Surface properties of the poly(HMDSO) thin film were investigated by water contact angle measurement and atomic force microscopy (AFM). Water vapor transmission rate (WVTR) value was obtained by an electrical calcium test (Ca test) at 85 °C and 85% relative humidity condition. It was confirmed that the poly(HMDSO) thin film exhibited excellent water vapor barrier capability. WVTR value of the PEN film coated with poly(HMDSO) deposited with a mixture of argon and oxygen (Ar: O2 = 2: 8) was 5.09 g/m2-day, which is much lower than 18.4 g/m2-day of a bare PEN film.

Wrinkling poly(trimethylene 2,5-furanoate) free-standing films: Nanostructure formation and physical properties

Polymer nanostructures were developed on fully bio-based poly(trimethylene furanoate) (PTF) films, by using the technique of Laser Induced Periodic Surface Structures (LIPSS). We found that irradiation times between 1 and 8 min allowed the formation of periodic and nanometric ripples, when using an UV pulsed laser source at a fluence of 8 mJ/cm2. The wrinkled surfaces were studied by a combined macro- and nanoscale approach. We evaluated possible physicochemical changes taking place on the polymer surface after irradiation by infrared spectroscopy, contact angle measurements and atomic force microscopy. The macroscopic properties of PTF showed almost no changes after nanostructure formation, differently from the results previously found for the terephthalic counterparts, as poly(ethylene terephthalate), PET, and poly(trimethylene terephthalate), PTT. At the nanoscale, the surface mechanical properties of the nanostructured PTF were found to be improved, as evidenced by force spectroscopy measurements. In particular, stiffer surfaces characterized by an increased Young's modulus were measured for the nanostructured sample.

Facile Method of Solvent-Flushing To Building Component Distribution within Photoactive Layers for High-Performance Organic Solar Cells.

Suitable donor and acceptor distribution in the blended photoactive layer benefits the charge transfer and exciton separation to boost the performance of organic solar cells (OSCs). Herein, we propose a universal solvent-flushing method for building component distribution in photoactive layers based on the different solubilities of the donor and acceptor in acetylacetone (Acac). The donor and acceptor concentration distribution through the photoactive layers is investigated by the time-of-flight secondary-ion mass spectroscopy, and the surface concentration changes are examined by contact angle measurements and atomic force microscopy tests. The charge-transfer properties of OSCs before and after Acac flushing are further investigated by the rectification ratio and light intensity-dependent Jsc and Voc measurements. For inverted OSCs based on PBDB-TF:IT-4F, the power conversion efficiency (PCE) enhances from 12.87 to 14.05%, and for a PBDB-TF:Y6-based device, the PCE also significantly increases from 15.40 to 16.51% because of greatly enhanced Jsc and FF, benefited from enhanced charge transport and suppressed charge recombination by solvent-flushing. Our findings suggest that solvent-flushing is a simply processed and easily controlled method to achieve vertical component distribution in photoactive layers to boost the performance of OSCs.