Surface Properties Of Substrates Research Articles

Effect of wettability and surface free energy of collection substrates on the structure and morphology of dry-spun cellulose nanofibril filaments

Utilization of cellulose nanofibrils (CNF) for filament production is a comparatively new approach, which can broaden nanocellulose applications by providing continuous long filaments suitable for composite and textile applications. Methods are proposed for the spinning of filaments from cellulose nanofibril suspensions, which are mainly categorized into two groups, i.e. dry-spinning and wet-spinning. For the dry-spinning method, the substrate on which the filament is spun will have a significant influence on the properties of the filament because the as-spun CNF will initially contact it. In this work, the influence of different collection substrates on the properties of CNF filament was studied. Filaments with an average diameter of 0.1 mm were spun on different collection substrates including Teflon tape, Teflon film and glass. The influence of adding oil, as a friction modifier, on the surface properties of the substrate and the structure of the resultant filaments was evaluated. Wettability of each substrate in the absence of oil, and the presence of a thin layer and a thick layer of oil was studied. Circularity of the filaments was measured using image analysis of the cross sections and was correlated with the surface properties of the substrates. It was found that while the surface properties of the collection substrate were related to the uniformity and cross section circularity of the filaments, those spun on a thick layer of oil had the best circular shape irrespective of the substrate material. The results of this study can be used to optimize dry-spinning of CNF filaments.

Microstructure and Wear Behaviour of Ti Reinforced HVOF Coating

In order to improve the wear resistance and biocompatibility of titanium, which is well known as a common orthopaedic and dental implants material, aluminium oxide (Al2O3)-hydroxyapatite (HA) composite coatings were deposited onto titanium substrate using high velocity oxygen fuel (HVOF) thermal spraying process.The microstructure of the Ti reinforced HVOF coating was investigated by scanning electron microscopy (SEM) and phase identification was performed using X-Ray diffraction techniques (XRD). The surface properties of the titanium substrate before and after Al2O3-HA coating deposition in terms of roughness and wear resistance, using pin on disk method, were determined.The obtained results showed that Al2O3-HA coatings can extremely improve the wear resistance of the titanium substrate. A higher roughness of the coating evidently has a positive effect onto the adhesion of the implant osseointegration.

Another Approach to Characterize Particle Distribution during Surface Composite Fabrication Using Friction Stir Processing

Surface composite fabrication through Friction Stir Processing (FSP) is evolving as a useful clean process to enhance surface properties of substrate. Better particle distribution is key to the success of surface composite fabrication which is achieved through multiple passes. Multiple passes significantly increase net energy input and undermine the essence of this clean process. This study proposes a novel approach and indices to relate the particle distribution with the FSP parameters. It also proposes methodology for predicting responses and relate the response with the input parameter. Unit stirring as derived parameter consisting of tool rotation speed in revolutions per minute (rpm), traverse speed and shoulder diameter was proposed. The particle distribution was identified to be achieved in three stages and all three stages bear close relationship with unit stirring. Three discrete stages of particle distribution were identified: degree of spreading, mixing and dispersion. Surface composite on an aerospace grade aluminum alloy AA7050 was fabricated successfully using TiB2 as reinforcement particles. FSP was performed with varied shoulder diameter, rotational speed and traversing speed and constant tool tilt and plunge depth using single pass processing technique to understand the stages of distribution. Significant relationships between processing parameters and stages of particle distribution were identified and discussed.

Contact electrification efficiency dependence on surface energy at the water-solid interface

Liquid-solid contact electrification is a useful mechanism to harvest wasted micromechanical energy. In this study, we investigate how the surface properties of a solid substrate affect contact electrification efficiency. Substrate surfaces were modified from hydrophilic to hydrophobic by changing the density of self-assembled monolayers (SAMs) on a SiO2 surface. A substrate with a partially-covered SAM exhibited superior performance. The partially-covered SAM substrate is hydrophobic enough to induce quick dewetting of water from the surface and sufficiently electronegative to induce a high charge density on the surface. The quick dewetting results from the aliphatic tail groups of the SAM and -OH groups make the SiO2 surface electronegative; these two competing properties can be simultaneously obtained by optimizing the SAM density. Our findings contribute to the understanding of contact electrification in liquid-solid-type energy-harvesting devices and advance the strategies to maximize the electrification efficiency by optimizing surface geometries and properties.

Surfactant-Free Synthesis of Graphene Oxide Coated Silver Nanoparticles for SERS Biosensing and Intracellular Drug Delivery

Surface-enhanced Raman scattering (SERS) has attracted increasing attention in the field of biochemical sensing since its discovery in 1970s, in virtue of its ultrahigh sensitivity to extremely low concentration of analyte. The performance of SERS biosensing strongly relies on the surface properties of SERS substrates, which are generally noble metallic nanoparticles. Surfactants have always been used for the preparation of nanoparticles to maintain the stability of nanocolloids, which greatly affect the efficiency of SERS sensing due to the space blocking between SERS substrates and analytes, as well as the interference of intrinsic Raman signals from surfactant themselves. Herein, without adding any surfactant, we synthesized nanosized graphene oxide (NGO) coated silver nanoparticles (Ag@NGO), which were used as efficient SERS substrates, taking the advantages of surfactant-free surface with inert protective effect of the GO shell. The Ag@NGO nanoparticles demonstrated excellent SERS sensing capability ...

Microstructural control by substrate heating in Pulse-DC sputtering induced thermoelectric Ge2Sb2Te5 thin films

Optimization of substrate heating during sputtering processes is essential to obtain desired microstructures of deposited thin films, as it provides the required energy flux during the nucleation and growth. In this work, Ge2Sb2Te5 thin films were prepared by a pulsed-DC magnetron sputtering process at optimized plasma conditions (pulsed frequency and pulse reversal time). The effect of substrate heating, in temperature range of 250–450 °C, was systematically investigated on the process throughput and various properties i.e. microstructure, morphology, atomic composition, carrier concentration, mobility and Seebeck coefficient of deposited films. The substrate heating was found to be required to obtain films in cubic crystalline phase. Through the optimization of substrate temperature, process throughput and surface properties, electrical properties as well as thermoelectric power factors were enhanced. The maximum power factor value of thin films was achieved as 0.77 mW m–1 K–2 for the substrate temperature as 400 °C.

Solid-Surface Modification with Two-Dimensionally Ordered Oriented Molecular Films

The surface properties of solid substrates have a considerable impact on many physical, chemical, and electrochemical events occurring at a materials interface, and thus the control of chemical and physical properties of solid surfaces (e.g., surface morphology and energy, wettability, and adhesiveness) provides a key technology in many practical applications. As a useful approach for this purpose, the formation of self-assembled monolayers (SAMs) has widely been used, which relies on specific bonding between polar functional groups of organic molecules and outermost surface elements of inorganic substrates. However, this approach cannot be applied for the modification of polymer substrate surfaces, which are devoid of any effective binding site against polar functional groups. Here we report a new type of organic surface modifier consisting of a paraffinic tripodal triptycene, which undergoes controlled self-assembly not only on inorganic substrates but also on polymer substrates, resulting in a completely oriented molecular thin film like SAMs. The formation of this molecular film does not rely on specific chemical bonding but on a unique assembling property of the molecular building block capable of forming 2D (hexagonal triptycene array) + 1D (layer stacking) structure regardless of the types of substrates. In this presentation, an application of this molecular film to organic electronic devices, which can enhance device performances, will also be described.

The enhanced abrasion resistance of an anti-fingerprint coating on chrome-plated brass substrate by integrating sputtering and atmospheric pressure plasma jet technologies

We demonstrate the procedure of fabricating an anti-fingerprint coating on plated-Cr/brass substrates by the combination of two processes: (1) Sputtering and (2) Atmospheric pressure plasma jet (APPJ). APPJ surface treatment on sputtered-SiOx glue layer on plated-Cr/brass substrate is conducted to improve its surface property to be hydrophilic for chemical bonding with an anti-fingerprint agent (AF-C01). The results show that the surface energy of original substrate are evolving from 44.2 mN/m to 60.8 mN/m and 76.9 mN/m for the sputtered-SiOx film and APPJ-treated SiOx film, respectively. Subsequently, the spin-coating process using a commercialnt (AF-C01 agent for the prepared sample is implemented. The hydrophobicity of anti-fingerprint characteristics for all of the samples with a quite low surface energy around 10.5 mN/m are obtained. For practical evaluation of abrasion behavior, a good abrasion resistance of AF/APPJ-treated SiOx/plated-Cr/brass sample under 1000 g-steel wood loading is evidently obtained from the slow variation of water contact angle value. The results demonstrate that the feasibility of integrating APPJ process on the sputtered-SiOx film for improving the surface properties of chrome-plated brass substrate is practically achieved.

Tuning of elasticity and surface properties of hydrogel cell culture substrates by simple chemical approach

When designing materials for tissue engineering applications various parameters characterizing both materials and tissue have to be taken into account. The characteristics such as chemistry, elasticity, wettability, roughness and morphology of the substrate’s surface have significant impact on cell behavior. The paper presents biopolymer (collagen/chitosan) based hydrogel materials with tunable elasticity and surface properties useful for fabrication of substrates for cell culture. Using simple chemical approach involving the change in concentration of crosslinking agent (genipin) and composition of the reaction mixture the hydrogels characterized with various features were obtained. Detailed analysis of morphology, topography, roughness and elasticity of surface performed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and rheological measurements has shown that the topographical aspects and roughness parameter can be modulated in nanoscale regime (13–47 nm). Substrate’s elasticity could be modified in a wide range (0.2–270 kPa). Biological in vitro studies on fibroblasts behavior revealed that the materials prepared provide satisfactory conditions for cell culture, ensuring their high viability, good adhesion and normal morphology. The genipin crosslinked collagen-chitosan hydrogels characterized by denser fiber structure, higher elasticity and lower surface roughness are the most attractive supports for fibroblasts cultivation. The results obtained indicate that the properties of the materials developed can be easily tailored to the needs of the given type of cells.

Properties of Al-Ga co-doped ZnO semiconductor thin films deposited on polyethylene terephthalate substrates by radio frequency magnetron sputtering

Al and Ga co-doped ZnO (AGZO) semiconductor thin films were deposited on polyethylene terephthalate (PET) substrates by radio frequency magnetron sputtering. Prior to oxide thin film deposition, the hydrophilicity of the surface of the PET substrate was increased by corona discharge treatment. In this study, the influence of corona discharge power on the surface properties of the PET substrates and the effect of substrate temperature on the physical properties of PET/AGZO thin film samples were investigated. After corona discharge treatment to modify the surfaces of the PET substrates, drastic decreases in the contact angle of water on the PET substrates demonstrated that the corona discharge treatment changed the surface wettability of the PET substrates. Experimental results showed that increasing the substrate temperature from room temperature to 135 °C significantly enhanced the crystallinity, reduced the surface roughness, and improved the electrical properties of the AGZO thin films. The AGZO thin films deposited on PET substrates at 135 °C had the highest Hall mobility of 5.5 cm2/Vs.

Biofilm development, activity and the modification of carrier material surface properties in moving-bed biofilm reactors (MBBRs) for wastewater treatment

ABSTRACTIn the last decades, moving-bed biofilm reactors (MBBRs) have found a niche in the treatment of municipal and industrial wastewaters due to advantages of compactness, simplicity, stability and increased reaction rates. Recently, the material surface properties of MBBR carriers and their modification have been investigated, as reviewed herein, in order to enhance the control of microbial attachment and biofilm development, and MBBR performance by faster reactor startups or increased specific activity per surface area. Biofilm formation is a complex process influenced by the solid substratum surface properties and microbial composition and characteristics. MBBR carriers can be made to facilitate biofilm formation by modifying their physico-chemical surface characteristics using blended polymers, mixed materials, coatings and incorporating different chemical functional groups. The chemical modification of the substratum polymeric surface for biofilm treatment reactors has comprised plasma oxidation treatment, radiolysis in a gas phase, liquid-phase oxidative treatment and polymer grafting. This review focusses on carrier material surface properties, the modification of such properties and carrier material choices relevant to biofilm development and functionality of MBBRs, in order to identify opportunities and challenges in future biofilm carrier development.

Hydrophobic ultrathin films formed by fluorofunctional cage silsesquioxanes

The usefulness of fluorofunctional cage silsesquioxanes (POSS) as coating materials effectively changing the surface properties of model substrates was analyzed. Five fully condensed silsesquioxanes (containing two types of organic groups attached to the Si-O cage: octafluoropentyloxypropyl (OFP) and trimethoxysilylethyl (TMS) at different ratios, one monofunctional derivative with OFP groups only and one open cage POSS derivative with three OFP and seven isobutyl groups as organic substituents were investigated. All POSS derivatives were applied to enhance hydrophobicity of quartz or glass plates by deposition of thin LB film transferred from the water subphase. Then, by comparison of water contact angles (WCA) on modified surfaces the effect of silsesquioxane structure (i.e. the TMS and fluoroalkyl group contents as well as the structure of silicon-oxygen cage) on hydrophobic properties was determined. Moreover, the texture of LB films formed by POSS considered was analyzed using the AFM technique. It has been established that the hydrophobizing properties of silsesquioxanes are considerably influenced not only by the number of OFP groups, but also by the silsesquioxane structure. The most effective appeared to be the open cage OFP-POSS derivative which produced coatings with water contact angles (WCA) equal to about 100 deg. Additionally the POSS derivatives studied were also used for dip-coating and spin-coating surface modification. The study has shown that fluorofunctional POSS derivatives can be effective hydrophobizing agents. Additionally applying the LB technique for surface modification allows obtaining substrate of enhanced hydrophobicity by using vanishingly small amount of the modifying substance in comparison to the dip-coating and spin-coating method, which is especially important from the economic viewpoint.

AM metal substrates for inkjet-printing of smart devices

A study to characterize surface and structural properties of 3D-printed metal substrates for multilayer inkjet-printing is presented. Such substrates can enable and alleviate the fabrication of smart and functional packages, implants or spare parts. For the characterization, a multilayer structure composed of an insulating layer and a superposed conductive layer is inkjet-printed onto the various 3D-printed metallic substrates. The printing is done using equivalent settings for all substrates. The characterization is based on microscopic and Focused Ion Beam (FIB) images, as well as profilometer and contact angle measurements of the substrates. Furthermore, microscopic images and four-point-probe resistance- and profilometer measurements are carried out, to gain insight into the quality of the multilayer print. We show the diversity in surface and structural properties of 3D-printed substrates, also for those fabricated using the same process. Also, the 3D-printed samples exhibit different wettability properties than metals processed using standard processes. Finally, we can also demonstrate the suitability of selected substrates for inkjet-printing.

Ultra-high sensitive substrates for surface enhanced Raman scattering, made of 3 nm gold nanoparticles embedded on SiO2 nanospheres

The surface properties of substrates made of 3 nm gold nanoparticles embedded on SiO2 nanospheres enabled fingerprint detection of thiabendazole (TBZ), crystal violet (CV) and 4-Aminothiophenol (4-ATP) at an ultralow concentration of ∼10−18 M by surface enhanced Raman spectroscopy (SERS). Gold nanoparticles of an average size of ∼3 nm were synthesized and simultaneously embedded on SiO2 nanospheres by the electron irradiation method. The substrates made from the 3 nm gold nanoparticles embedded on SiO2 nanospheres were successfully used for recording fingerprint SERS spectra of TBZ, CV and 4-ATP over a wide range of concentrations from 10−6 M to 10−18 M using 785 nm laser. The unique features of these substrates are roughness near the surface due to the inherent structural defects of 3 nm gold nanoparticles, nanogaps of ≤ 1 nm between the embedded nanoparticles and their high number. These produced an abundance of nanocavities which act as active centers of hot-spots and provided a high electric field at the reporter molecules and thus an enhancement factor required to record the SERS spectra at ultra low concentration of 10−18 M. The SERS spectra recorded by the substrates of 4 nm and 6 nm gold nanoparticles are discussed.

Effect of Pulsed Current Frequency and Anodisation Time on Surface Properties of Electropolished and Nonelectropolished Titanium Substrates

Surface characteristics of anodic films formed on electropolished and nonelectropolished titanium substrates have been evaluated using different sets of anodisation parameters at room temperature. Surfaces were analysed by light microscopy, Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. The formation of TiO2anatase phase was only detected on nonelectropolished substrates and there seems to be a larger amount of anatase as samples are anodised; consequently, the smallest crystals were obtained at the highest frequency of pulsed current. EIS results showed that there is no difference in the degree of compactness along the layer thickness.

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films.

It is well-known that substrate surface properties have a profound impact on the morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution-coated semiconducting polymers, as the substrate-directed thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We perform in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing donor-acceptor (D-A) conjugated polymers. We find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering, and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate leads to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step toward establishing design rules and understanding the critical role of substrates in determining morphology of solution-coated thin films.

Effect of surface modifications by abrasive water jet machining and electrophoretic deposition on tribological characterisation of Ti6Al4V alloy

Abrasive water jet (AWJ) milling has speedily developed in popularity due to its adaptability and fast production of blind features like channels, pockets etc. But the surface property of AWJ-milled samples was found to be poor, restricting the process of being commercially used widely. In this work, a two-step methodology has been tried to modify the surface properties of Ti6Al4V substrate, which includes fast fabrication of miniaturised channel using AWJ technique followed by electrophoretic deposition (EPD) of hydroxyapatite-carbon nanotube (HAp-CNT) coating. The fretting wear test divulges the enhanced wear resistance of synergistically textured Ti6Al4V substrate with EPD HAp-CNT, due to its lower coefficient of friction (0.22 ± 0.0) and wear depth (− 18.1636 μm) when compared with that of textured Ti6Al4V (0.27 ± 0.005 and − 18.8221 μm, respectively). The coefficient of friction and wear depth were observed to be highest for bare Ti6Al4V sample (0.41 ± 0.007 and − 27.4985 μm, respectively). The observed increment in wear resistance is due to the textured channels trapping the wear debris and a decrease in the real contact area due to the coating of HAp-CNT. Thus, fabrication of micro-channels by AWJ combined with HAp-CNT coating may provide potential self-lubrication and enhance damage tolerance of Ti6Al4V alloy for biomedical and manufacturing applications.

Investigation of dielectric substrates on electrical and optical performance of wafer-scale graphene using non-contact methods

Here we systemically discussed the influence of dielectric substrates on the surface morphology, electrical and optical performance of transferred graphene. The electrical properties were investigated using a microwave-probing technique without metal-graphene contact. We found that a complex mechanism governed the influence of the surface properties of the dielectric substrates, such as morphology, hydrophilicity, crystallinity, and polarization, on the performance of the graphene. We also found that graphene on r-Al2O3 was more effective for graphene-based devices with a high carrier mobility of ∼5000 cm2 V−1 s−1. This provides a new method to choose the most suitable substrate for fabricating graphene-based devices.

Surface modification of β-phase Ti implant by hydroaxyapatite mixed electric discharge machining to enhance the corrosion resistance and in-vitro bioactivity

The study presented an innovative method for surface modification of β-phase titanium alloy using hydroxyapatite mixed electric discharge machining (HAM-EDM). The process enables one to deposit in-situ a biomimetic nano-porous HA-containing layer while shaping the base titanium, hence modifying the surface properties of the original substrate. A series of the dedicated HAM-EDM on titanium alloys have been conducted. Surface integrity, topography, and elemental composition of the modified surface were investigated by FE-SEM, EDS, XRD, and indentation techniques, while in vitro cell study was performed to evaluate biocompatibility and cell attachment of the treated surface. The morphology characterization results revealed that a natural bone-like nano-porous surface topography has been imparted on the β-phae Ti implant surface using the HAM-EDM. The EDS and XRD examinations showed that the deposited layer comprised of Ti, Nb, Ta, Zr, O, Ca and P elements and formed biocompatible phases such as Ca3(PO4)2, CaZrO3, Nb8P5, CaO, TiP, Nb4O5, and TiO2, TiH on the β-Ti implant surface, which improved the bioactivity of the alloy and beneficial for the promotion of osseointegration. The results revealed that a 18–20μm thick recast layer containing biocompatible phases was generated, which has excellent metallurgical bonding with the base surface and offered mechanical interlocking to delamination. The HA deposited surface shows am improved hardness of 1275HV which is 3-fold higher than the untreated surfaces; predominantly owing to the deposition of hard oxides on the modified surface. The HA-deposited bioceramic layer presented an excellent and higher corrosion resistance as compared to EDMed and un-treated specimens in simulated body fluid. The in-vitro bioactivity results confirmed that the nano-porous HA-containing layer exhibited the superior bioactivity and promotes adhesion, growth, proliferation, and differentiation of human osteoblastic MG-63 cells.

Micro- and nano-surface structures based on vapor-deposited polymers.

Vapor-deposition processes and the resulting thin polymer films provide consistent coatings that decouple the underlying substrate surface properties and can be applied for surface modification regardless of the substrate material and geometry. Here, various ways to structure these vapor-deposited polymer thin films are described. Well-established and available photolithography and soft lithography techniques are widely performed for the creation of surface patterns and microstructures on coated substrates. However, because of the requirements for applying a photomask or an elastomeric stamp, these techniques are mostly limited to flat substrates. Attempts are also conducted to produce patterned structures on non-flat surfaces with various maskless methods such as light-directed patterning and direct-writing approaches. The limitations for patterning on non-flat surfaces are resolution and cost. With the requirement of chemical control and/or precise accessibility to the linkage with functional molecules, chemically and topographically defined interfaces have recently attracted considerable attention. The multifunctional, gradient, and/or synergistic activities of using such interfaces are also discussed. Finally, an emerging discovery of selective deposition of polymer coatings and the bottom-up patterning approach by using the selective deposition technology is demonstrated.