Surface Properties Of Substrates Research Articles

On the substantial mechanical reinforcement of Polylactic Acid with Titanium Nitride ceramic nanofillers in material extrusion 3D printing

Titanium nitride (TiN) is known as an ultra-hard ceramic, mainly deployed in thin hard coating applications for improving the substrate's surface properties. Therefore, investigating its effectiveness as a reinforcement for thermoplastics in material extrusion (MEX) 3D printing (3DP) has great potential for the development of materials with superior enhancements, which are sought after, as Additive Manufacturing (AM) continuously expands its field of applications. In this study TiN in nano-powder was induced into Polylactic Acid (PLA) thermoplastic and a thermomechanical process was used to produce nanocomposites at various concentrations for 3DP filament. 3D printed specimens using MEX were used for their mechanical characterization and for investigating the thermal, structural, and morphological properties of the nanocomposites. The new materials' performance was evaluated in terms of the TiN filler loading. It was found that Titanium Nitride nanoparticles can upgrade the mechanical response of PLA when used in MEX 3DP. A 43.4% improvement in the tensile strength and a 51.5% enhancement in the flexural strength is reported herein for 4 wt% TiN loading nanocomposite. The effect on the process cost from the addition of the filler was also evaluated, indicating that the process is cost-effective with no processability issues.

Influence of the crystallographic texture of ITO on the electrodeposition of silver nanoparticles.

The electrochemical control over nucleation and growth of metal nanoparticles on foreign substrates is an active field of research, where the surface properties of the substrate have a key role in nucleation dynamics. Polycrystalline indium tin oxide (ITO) films are highly desired substrates for many optoelectronic applications, for which the only parameter that is often specified is the sheet resistance. As a result, growth on ITO is highly irreproducible. Here, we show that ITO substrates with same technical specifications (i.e. sheet resistance, light transmittance and roughness) and supplier may still have different crystalline texture, which we find it has a strong impact on the nucleation and growth of silver nanoparticles during electrodeposition. We find that the preferential presence of lower index surfaces leads to few orders of magnitude lower island density, which is strongly dependent on the nucleation pulse potential. By contrast, the island density on ITO with preferential 〈111〉 orientation is barely affected by the nucleation pulse potential. This work highlights the importance of reporting the surface properties of polycrystalline substrates when presenting nucleation studies and metal nanoparticle electrochemical growth.

Peptide GL13K releasing hydrogel functionalized micro/nanostructured titanium enhances its osteogenic and antibacterial activity

Bacterial infection and the subsequent lack of osseointegration are two of the main problems encountered during the early stage of implantation. To resolve these issues, in this study, the micro/nanostructure on titanium surface was fabricated by dual-acid treatment and anodic oxidation, and then GelMA hydrogel loaded with GL13K was coated onto the micro/nanostructured titanium. The surface properties of different titanium substrates were characterized by scanning electron microscopy, atomic force microscope, water contact angle measurement, and in vitro release of GL13K. The results demonstrated that peptide GL13K releasing hydrogel was successfully modified onto the micro/nanostructured titanium and GL13K displayed an effective controlled release. In vitro cell experiments including cytoskeleton observation, cell viability, phosphatase activity, mineralization and the expression of osteogenic related genes proved that the peptide GL13K releasing hydrogel modified micro/nanostructured titanium had good biocompatibility, promoted osteoblast differentiation. In vitro antibacterial experiments showed that it also can prevent the growth of gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria by the release of GL13K. This study demonstrates titanium surface modification that allows for the development of anti-bacterial titanium implants.

Stable Ultrathin Ag Electrodes by Tailoring the Surface of Plastic Substrates for Flexible Organic Light-Emitting Devices.

Flexible transparent metal electrodes (FTMEs) have significant application potentials in the fields of flexible optoelectronic devices due to their outstanding optical transmittance and electrical conductivity. However, obtaining excellent optoelectrical properties and mechanical flexibility of FTMEs is challenging because ultrathin metal layers usually follow an island growth mode. In this paper, flexible transparent ultrathin Ag electrodes with high mechanical stability and good optoelectrical properties were exploited by tailoring the surface properties of plastic substrates with ultraviolet-ozone (UVO) treatment for regulating the nucleation and growth kinetics of Ag films. The composite transparent electrodes of Ag (9 nm)/MoO3 (20 nm) fabricated on the UVO-treated polyethylene terephthalate (PET) substrates possess a low sheet resistance of ∼7.9 Ω/sq, a high optical transmittance of ∼87.2% at 550 nm, a long-period environmental stability of 30 days (∼65 °C, ∼80% humidity), and excellent mechanical flexibility of 100,000 bending cycles at a bending radius of 1.5 mm. These properties are derived from the surface treatment of PET substrates by UVO, which increases substrate surface energy and produces chemical nucleation sites of the phenolic hydroxyl groups. The phenolic hydroxyl groups generated on the PET surface not only provided efficient nucleation sites for subsequent Ag film growth but also formed C-O-Ag bonds between the substrate surface and the Ag layer, which act as "anchor chains" to fix firmly the Ag atoms on the substrate surface. As a universal applicability strategy, the composite electrodes on the UVO-treated polyethylene naphthalate (PEN) and norland optical adhesive 63 (NOA63) substrates also possess excellent optoelectrical properties and mechanical flexibility. Based on the ultrathin Ag composite electrodes, the flexible white organic light-emitting devices with PET, PEN, and NOA63 as substrates present the maximum current efficiencies of 53.0, 77.0, and 65.2 cd/A, respectively.

Strategies for controlling biofilm formation in food industry

Foodborne pathogen poses a threat to the food industries as many outbreaks have been found to be associated with biofilm formation. The formation of biofilm is a self-protection growth pattern of bacteria, which increases post-processing contamination and risk to public health. It is difficult to eliminate the biofilm in the food industries, since the biofilm cells have a barrier preventing or lessening the contact with environmental stresses, antimicrobial agents and the host immune system. Bacterial biofilm formation is a complex process, including initial attachment stage, irreversible attachment stage, biofilm development stage, biofilm maturation stage, and biofilm dispersion stage. The genetic mechanism, substratum and bacterial cell surface properties involve in the biofilm formation. The biofilm inhibition methods studied are physical treatment, chemical and biochemical treatment. The potential green and safe biochemical method attracts more attention, especially, the novel strategies using the safe biochemical agents (essential oils, enzymes, biosurfactants, others) constantly emerged. The review emphasized on effective strategies for inhibiting biofilm formation in different stages (initial irreversible attachment, formation, and maturation) by use of biochemical agents, aiming to provide new insight into biofilm control in food industry thus improving food quality and safety.

Antimony selenide as a buffer layer for high-efficiency and highly crystalline germanium monoselenide thin-film solar cells

Germanium monoselenide (GeSe) is a photosensing material that has recently received considerable research attention. Crystallization of the GeSe absorption layer is the key to determining the power conversion efficiency (PCE) of GeSe thin-film solar cells, which is influenced by substrate surface properties. In this study, we prepared an antimony selenide (Sb2Se3) buffer layer on an electron-transport layer (ETL) to modulate the subsequent growth of the GeSe absorption layer. The results showed that increasing the preparation temperature of the Sb2Se3 buffer layer (TSbSe) can effectively promote its crystallization. A highly crystalline GeSe absorption layer could be heteroepitaxially grown on a highly crystalline Sb2Se3 buffer layer. When TSbSe was 275 °C, the PCE of the GeSe solar cell was enhanced to 2.673 %. Our results will enable the fabrication of high-performance GeSe optoelectronic devices.

Layer-by-layer assembly of alginate/Ca2+ as interlayer on microfiltration substrate: Fabrication of high selective thin-film composite forward osmosis membrane for efficient heavy metal ions removal

Forward osmosis (FO) technology has the merit potential to remove heavy metal ions from wastewater. However, the deficiency of FO membranes with low selectivity and permeability has hampered the scale-up and development of this technology. In this work, we coated a hydrophilic alginate/Ca2+ thin layer through the layer-by-layer (LbL) assembly as an interlayer on polyethersulfone (PES) microfiltration (MF) substrate to enhance the separation performance of the thin-film composite (TFC) membrane. The interlayer thickness was controlled by the LbL cycles (1–7 cycles), and its effect on surface properties of substrates in terms of hydrophilicity and pore size was investigated thoroughly. Then the influence of interlayer LbL cycles on the polyamide (PA) synthesis through interfacial reaction was studied. Results show that the interlayer prevents the PA layer's intrusion into the substrate pores and provides a hydrophilic and smooth surface to synthesize a defect-free PA layer. SEM images show that a dense, uniform, and defect-free PA rejection layer was formed on interlayer-coated MF substrates. FO performance result also verified the positive effect of interlayer on TFC membrane performance, where TFC-LbL.5 membrane (with 5 LbL cycles of alginate/Ca2+) showed 2 times higher water flux than control TFC membrane (23.3 LMH compared to 9.2 LMH). In the TFC-LbL.5 membrane, the defect-free PA active layer formed on the alginate/Ca2+ interlayer acted as a favorable barrier for different heavy metal ions (Cr3+, Co2+, and Hg2+) with the rejection of more than 99% under FO mode. This work offers a novel opportunity for the practical construction and development of high-efficiency TFC-FO membranes for heavy metal removal applications.

Plasma-Modified PI Substrate for Highly Reliable Laser-Sintered Copper Films Using Cu2O Nanoparticles.

Plasma modification of polyimide (PI) substrates upon which electrical circuits are fabricated by the laser sintering of cuprous oxide nanoparticle pastes was investigated systematically in this study. Surface properties of the PI substrate were investigated by carrying out atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Experimental results show that surface characteristics of PI substrates, including surface energy, surface roughness, and surface binding significantly affected the mechanical reliability of the sintered copper structure. Among the plasma gases tested (air, O2, Ar-5%H2, and N2-30%H2), O2 plasma caused the roughest PI surface as well as the most C=O and C–OH surface binding resulting in an increased polar component of the surface energy. The combination of all those factors caused superior bending fatigue resistance.

Self-Assembled 4-Aminopyridine Monolayer as a Nucleation-Inducing Layer for Transparent Silver Electrodes

The role of a self-assembled monolayer obtained by vacuum deposition of 4-aminopyridine (4-AP), a small organic molecule having amine and pyridine groups, as a metal nucleation inducer and adhesion promoter was verified, and the applicability was evaluated. 4-AP deposited to an extremely thin thickness effectively changed the substrate surface properties, increasing the nucleation density of silver (Ag) more than 3 times and eventually forming a more transparent, low-resistance Ag thin film. The optical transmittance of the Ag thin film, which was less than 60% when 4-AP was not applied, could be increased to about 77% by simply applying 4-AP, and the electrical resistance could be lowered from 37 to 14 Ω/square at the same time. Transmittance could be further improved to higher than 90% by depositing an antireflection layer for use as a transparent Ag electrode. It was also verified that 4-AP not only serves as a nucleation inducer but also contributes to improving interfacial adhesion. The Ag transparent electrode using 4-AP provided the improved performance of the organic light-emitting device due to higher transmittance, lower resistance, and surface roughness. Small organic molecules including functional groups that can be vacuum deposited, such as 4-AP, are expected to be used as surface pretreatment materials for various depositions because they can be easily patterned and can efficiently modify the surface even with extremely thin thickness.

Understanding the Formation Process of Perovskite Layers Grown by Chemical Vapour Deposition

This work aims at extending the understanding of the formation processes of (Cs0.07FA0.93)PbI3 perovskite layers deposited by a two-step vapour method. In a first step, an inorganic CsI/PbI2 precursor stack is deposited by thermal evaporation (TE). A chemical vapour deposition (CVD) is then used to convert the precursor into the perovskite layer by reaction with a chemical vapour of formamidinium iodide (FAI). Here we show how crystallinity and morphology of the TE precursor layer are both influenced not only by the substrate surface properties but also by the thermal treatment in the initial phase of the CVD process. Furthermore, we provide insights on the evolution of perovskite film formation and show how a uniform elemental composition is achieved by the diffusion of cesium through PbI2 during the CVD conversion reaction.

The concurrent enrichment of glycoproteins and phosphoproteins with polyoxometalate-covalent organic framework conjugate as the adsorbent

Polyoxometalates (POMs) have been explored to tailor the surface properties of substrates to satisfy the practical demands. Herein, the hydrophobicity of vinyl-containing covalent organic framework (COF) was regulated by modifying with 3-mercaptopropyltrimethoxysilane organofunctionalized tri-lacunary polyoxometalate (MPW9) through thiol-ene click reaction. The product was termed as COF-MPW9, with a specific surface area of 396 m2 g−1. The improved super hydrophilicity of COF-MPW9 provided favorable capability for the concurrent enrichment of glycoproteins and phosphoproteins. The adsorption capacities for the representative glycoprotein and phosphoprotein, i.e., immunoglobulin G (IgG) and β-casein (β-ca), were derived to be 378 mg g−1 and 740 mg g−1, respectively. Moreover, it was demonstrated that COF-MPW9 could selectively capture glycoproteins and phosphoproteins from human serum. This is potentially valuable for the ensuing study of glycoproteomics and phosphoproteomics.

Effect of PEG grafting density on surface properties of polyurethane substrata and the viability of osteoblast and fibroblast cells

The surface of Tecoflex SG-80A Polyurethane (PU) films was modified by grafting polyethylene glycol (PEG) chains at three different molar amounts (0.05, 0.10, and 0.15 mmol). The resulting substrata were characterized by FTIR-ATR, TGA, AFM, SEM and contact angle to assess the surface modifications occurred during the grafting reactions. Osteoblasts and fibroblasts were cultured with PU extracts for 24 h, and their cell viability and morphology were evaluated by CellTiterBlue assay, Crystal Violet staining and Live/Dead assay. FTIR and TGA results indicated that PEG chains were successfully grafted onto PU surfaces, specifically in the hard segment of PU forming allophanate groups as the PEG grafting density increased. SEM and AFM images suggest that PU substrata were partially covered by PEG, increasing the dispersive and basic components of the PU surface energy. It was found that extracts from PEG-grafted polyurethanes increased the osteoblast viability, although fibroblasts viability remained constant regardless PEG grafting density; in spite of this both cells presented a more spread morphology at the lower PEG grafting density. Our results showed that surface energy of PU substrata can be tuned by PEG grafting density; also, the PEG leached tends to increase the pH of culture medium which leads to a higher viability of osteoblasts; nevertheless, PEG grafting density should be optimized to promote a healthy cell morphology as alterations in its morphology were detected at higher concentrations.Graphical abstract

Titanium Surface Modification for Implantable Medical Devices with Anti-Bacterial Adhesion Properties.

Pure titanium and titanium alloys are widely used in dentistry and orthopedics. However, despite their outstanding mechanical and biological properties, implant failure mainly due to post-operative infection still remains a significant concern. The possibility to develop inherent antibacterial medical devices was here investigated by covalently inserting bioactive ammonium salts onto the surface of titanium metal substrates. Titanium discs have been functionalized with quaternary ammonium salts (QASs) and with oleic acid (OA), affording the Ti-AEMAC Ti-GTMAC, Ti-AUTEAB, and Ti-OA samples, which were characterized by ATR-FTIR and SEM-EDX analyses and investigated for the roughness and hydrophilic behavior. The chemical modifications were shown to deeply affect the surface properties of the metal substrates and, as a consequence, their bio-interaction. The bacterial adhesion tests against the Gram-negative Escherichia Coli and Gram-positive Staphylococcus aureus, at 1.5 and 24 h of bacterial contact, showed good anti-adhesion activity for Ti-AUTEAB and Ti-OA samples, containing a long alkyl chain between the silicon atom and the ammonium functionality. In particular, the Ti-AUTEAB sample showed inhibition of bacteria adhesion against Escherichia Coli of about one log with respect to the other samples, after 1.5 h. The results of this study highlight the importance of chemical functionalization in addressing the antimicrobial activity of metal surfaces and could open new perspectives in the development of inherent antibacterial medical devices.

Two Birds with One Stone: Using Indium Oxide Surficial Modification to Tune Inner Helmholtz Plane and Regulate Nucleation for Dendrite-free Lithium Anode.

Lithium metal has been considered as the most promising anode material due to its distinguished specific capacity of 3860mAh g-1 and the lowest reduction potential of -3.04V versus the Standard Hydrogen Electrode. However, the practicalization of Li-metal batteries (LMBs) is still challenged by the dendritic growth of Li during cycling, which is governed by the surface properties of the electrodepositing substrate. Herein, a surface modification with indium oxide on the copper current collector via magnetron sputtering, which can be spontaneously lithiated to form a composite of lithium indium oxide and Li-In alloy, is proposed. Thus, the growth of Li dendrites is effectively suppressed via regulating the inner Helmholtz plane modified with LiInO2 to foster the desolvation of Li-ion and induce the nucleation of Li-metal in two-dimensions through electro-crystallization with Li-In alloy. Using the In2 O3 modification, the Li-metal anode exhibits outstanding cyclic stability, and LMBs with lithium cobalt oxide cathode present excellent capacity retention (above 80% over 600 cycles). Enlightening, the scalable magnetron sputtering method reported here paves a novel way to accelerate the practical application of the Li anode in LMBs to pursue higher energy density.

Substrate-induced electrostatic potential varies composition of supported lipid bilayer containing anionic lipid

Supported lipid bilayers (SLBs) are artificial lipid bilayers at solid–liquid interfaces applied as cell membrane model systems. An advantage of the artificial system is that the lipid composition can be controlled arbitrarily. On the other hand, the SLB formation process and its efficiency are affected by the properties of the solid substrate surface. In this study, we investigated the effect of the electrostatic interaction between the negatively charged SiO2/Si substrate surface and the lipid bilayer membrane on the composition of binary SLBs comprising anionic and neutral lipids. The phase transition temperature and the area fraction of lipid domains of SLB were evaluated by fluorescence microscopy and the fluorescence recovery after photobleaching. The neutral lipid was preferably included in SLB, but the anionic lipid ratio increased with Ca2+ concentration during the SLB formation. The lipid composition in SLB can be controlled by modulating the substrate-induced electrostatic potential.

High-Efficiency Capture of Cells by Softening Cell Membrane.

The capture of circulating tumor cells (CTCs) by nanostructured substrate surface is a useful method for early diagnosis of cancer. At present, most methods used to improve the cell capture efficiency are based on changing substrate surface properties. However, there are still some gaps between these methods and practical applications. Here, a method is presented for improving cell capture efficiency from a different perspective, that is, changing the properties of the cells. Concretely, the mechanical properties of the cell membrane are changed by adding Cytochalasin D to soften the cell membrane. Furthermore, a corresponding theoretical model is proposed to explain the experimental results. It is found that cell softening can reduce the resistance of cell adhesion, which makes the adhesion ability stronger. The high-efficiency capture of cells by softening the cell membrane provides a potential method to improve the detection performance of CTCs.

Thermodynamic Modeling of Solvent-Assisted Lipid Bilayer Formation Process.

The solvent-assisted lipid bilayer (SALB) formation method provides a simple and efficient, microfluidic-based strategy to fabricate supported lipid bilayers (SLBs) with rich compositional diversity on a wide range of solid supports. While various studies have been performed to characterize SLBs formed using the SALB method, relatively limited work has been carried out to understand the underlying mechanisms of SALB formation under various experimental conditions. Through thermodynamic modeling, we studied the experimental parameters that affect the SALB formation process, including substrate surface properties, initial lipid concentration, and temperature. It was found that all the parameters are critically important to successfully form high-quality SLBs. The model also helps to identify the range of parameter space within which conformal, homogeneous SLBs can be fabricated, and provides mechanistic guidance to optimize experimental conditions for lipid membrane-related applications.

Instabilities of a shear-thinning fluid falling over an undulating porous layer

We investigate the stability of a fluid film with power-law rheology flowing down a porous nonplanar incline with periodic undulations. A model is implemented which accounts for filtration flow through the substrate. A reduction in dimensionality in the model is achieved by exploiting the assumed thinness of the liquid film relative to the wavelength of the bottom undulations. A steady flow is obtained and its linear stability determined through the application of Floquet–Bloch theory. A nonlinear stability analysis is also carried out by calculating the evolution of the perturbed steady flow by means of numerical simulations. • An investigation of instability of film flow down an uneven porous incline. • A power-law rheological model is implemented. • Film flow is coupled with the filtration flow through the porous medium. • Combined effects of surface tension, rheology and properties of substrate determined.

Local force titration of wood surfaces by chemical force microscopy

Chemical force microcopy, a variation of atomic force microscopy, opened the door to visualize chemical nano-properties of various materials in their natural state. The key function of this method is given by translating adhesion forces between a functionalized tip and the sample to chemical surface behavior. In force titration, these adhesion forces are studied in different pH buffers, which allows estimating the pKa value of the analyzed surface. Herein, we report the use of this method to study natural and chemically treated wood surfaces, which are of interest in sustainable material design. First, we show varying adhesion phenomena of OH- and COOH-functionalized tips on native spruce wood cells. Then, we demonstrate how peak force tapping with chemically functionalized tips can be used to estimate the pKa value of gold substrates (pKa ≈ 5.2) and different wood cell wall layers with high spatial resolution. Additionally, the swelling behavior of wood samples is analyzed in varying pH buffers. With the applied method, chemical surface properties of complex natural substrates can be analyzed.Graphical abstract

Influence of substrate surface roughness and moisture content on tensile adhesion performance of 3D printable concrete

3D concrete printing is of great potential to replace shotcrete for hard rock tunnel linings with the advantages of high surface quality and the avoidance of rebound. However, without spraying fresh concrete onto the excavated surface at a high speed, 3D printable concrete still faces challenges of achieving strong adhesion, which closely depends on the substrate surface properties. In this work, the influence of the substrate surface roughness and moisture content on the tensile adhesion of 3D printed concrete in the fresh and hardened state was studied. A tack test and a 3D concrete printing test were used to evaluate the tensile adhesion in the fresh state. Further, the tensile adhesion of 3D printed concrete in the hardened state was measured by a pull-off test and compared with that of mold cast samples. Results showed that the printed material could not completely fill macro rough textures due to the limited pressure at the nozzle. As a result, less contact at the interface was formed when the substrate surface roughness level increased, which subsequently compromised the tensile adhesion in the fresh and hardened state. Fortunately, the tensile adhesion in the fresh and hardened state can be improved by applying a coating onto the substrate beforehand. On the other hand, an increased moisture content enhanced the tensile adhesion in the fresh state due to surface tension, while it reduced the tensile adhesion in the hardened state in the context of 3D concrete printing which can be attributed to a higher water-to-cement ratio at the contact zone.