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Chemically modified polymer coatings have been synthesized using a blend of soft polymeric material polydimethylsiloxane (h-PDMS) incorporated with stiff polymer epoxy resin (EP) and was cross-linked using silane compatibilizer 3-aminopropyltriethoxysilane (APTES). A comparative analysis has been carried out between neat epoxy coating (N-EP) and epoxy–hydroxy-terminated polydimethylsiloxane (EP-hPD) blends to study the influence of blending ratio on various properties to cater marine applications. An increase of 144.4% in the Young’s modulus (E) and 37.5% increment in adhesion strength at 30 wt% h-PDMS content was observed as compared with N-EP. The water contact angle results demonstrated a substantial increase in contact angle from 52.3° to 90.1° at 30 wt% h-PDMS content as compared to N-EP. Taber abrasion results revealed a decrease in weight loss (mg/1000 cycles) by 24.1 and 17.7% at 10 and 30 wt% loading of h-PDMS in comparison to N-EP. The surface roughness of N-EP and 30 wt% EP-hPD blend were found to be 33.4 nm and 41.4 nm, respectively. To determine the applicability of the developed blend coatings obligatory tests such as field immersion study and chemical resistance evaluation were conducted, and optimum performance was manifested by EP-hPD blend at an EP:h-PDMS ratio of 70:30.
Cu films are widely used in electronics for interconnections. In some applications, reliable thin-film connecting elements having high electrical conductivity, mechanical stability and adhesion to a glass substrate are required. In this case the length of the elements amounts to tens of centimetres. In this paper, Cu was used as the basis for the connecting elements. To ensure high adhesion Cr was used as an underlayer. The paper investigates the structure, electrical conductivity, adhesion, defect formation of Cu, Cu-Cr, Cr-Cu-Cr thin-film conductors. As a result of the performed research, the regularities of changes of the film structure, electrical conductivity, adhesion, defect formation depending on the technological process parameters were established. Physical and technological mechanisms determining the observed patterns are considered. The research results are used in the device production technology.
A kind of novel Ni–P gradient coating/stannate conversion film was deposited on AZ91D magnesium alloy (AZ91D alloy) by an integrative method involved stannate conversion and electroless plating. The results indicated that using sodium hypophosphite concentrations varied as 5, 10, 22, 46, and 60 g/L in the bath, the electroless Ni–P gradient coating with typical cell morphologies was successfully prepared, and the structures transited from crystalline → microcrystalline → amorphous were obtained as increasing P content from 3.31 to 12.58 wt%. Furthermore, the corrosion morphologies, polarization curves, and the electrochemical impedance spectroscopy result indicated that the corrosion resistance of AZ91D alloy substrate was significantly improved and the corrosion resistance of Ni–P gradient coating was superior than that of stannate conversion film, which might be attributed to the gradient structure and rising P content with unique function.
Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things’ sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
The intracellular concentration of calcium ion ([Ca2+]i) is a critical regulator of cell signaling and contractility of vascular smooth muscle cells (VSMCs). In this study, we employed an atomic force microscopy (AFM) nanoindentation-based approach to investigate the role of [Ca2+]i in regulating the cortical elasticity of rat cremaster VSMCs and the ability of rat VSMCs to adhere to fibronectin (Fn) matrix. Elevation of [Ca2+]i by ionomycin treatment increased rat VSMC stiffness and cell adhesion to Fn-biofunctionalized AFM probes, whereas attenuation of [Ca2+]i by 1,2-Bis (2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid tetrakis (acetoxymethyl ester) (BAPTA-AM) treatment decreased the mechanical and matrix adhesive properties of VSMCs. Furthermore, we found that ionomycin/BAPTA-AM treatments altered expression of α5 integrin subunits and α smooth muscle actin in rat VSMCs. These data suggest that [Ca2+]i regulates VSMC elasticity and adhesion to the extracellular matrix by a potential mechanism involving changing dynamics of the integrin–actin cytoskeleton axis.
The aim of this research was to investigate the influence of substrate roughness on the adhesion and tribological performance of thin TiN coatings obtained by physical vapor deposition. For that purpose, substrates of AISI H13 steel with surface finishes of 0.06, 0.28 and 0.90 μm in Ra were coated with TiN under the same coating conditions. The chemical composition of the steel, as well as that of the TiN coating, were obtained using EDS analysis. Adhesion tests were carried out following the procedure of BSi 1071-8 standard while hardness was evaluated by ASTM C 1327-03. On the other hand, dry sliding friction tests were conducted with a pin-on-disk tribometer, according to the ASTM G 99-05 standard. This study showed that the roughness of the coating increases as the substrate roughness increases. Regarding adhesion and hardness, all the samples showed an adhesion class 1 according to the standard and a hardness value of 14.51 GPa. Nevertheless, the highest substrate roughness produced the best adhesion. On the other hand, the lowest values for the friction coefficient and wear behavior were obtained by the sample with the lowest substrate roughness of 0.06 µm. In addition, it was found that friction and wear increase when the substrate roughness increases.
The exotic characteristics of nanoscopic metallic materials bestows diverse functionalities that are increasingly being utilized for a broad range of applications. Polymer substrates present robust architectures for nanoparticle anchoring as well as modulating attendant size-induced aggregation. However, in principle, interfacial adhesion of a polymer-metal material system is weak, making the susceptibility to delamination a challenge. We have deposited copper particles on model polymer thin film and fibrous architectures to study adhesion behavior on these distinct geometries. The average sizes of copper nanoparticles deposited on electrospun fibers for metallization times of 3 and 5 minutes were 13 and 10 nm, whereas the metal island sizes under same metallization times on thin films was 79nm and 81nm. Scratch tests using a nanoindentation system were unable to generate macroscopic film delamination, but did exhibit apparent removal of individual particles, with adhesion forces of 14.9μN, 36μN, and 28.8μN obtained for films metallized for 1, 3, and 5 minutes respectively. Macroscopic tensile testing of fiber mats showed the metallization maintains conformity with the polymer ligament, albeit, with intermittent fracture of the conformal metal coating, signifying substantial adhesion exists between the metallic layer and the PAN fiber.
Evaluation of eleven candidate probiotic Lactobacillus strains isolated from human milk showed that some of the strains were well endowed with desirable cell surface and attachment attributes. The cell surface properties (hydrophobicity, auto-aggregation, attachment to collagen and HT-29 monolayer) of probiotic Lactobacillus species of human milk origin were compared with reference probiotic/ non-probiotic species and pathogenic strains. The bacterial adhesion to hydrocarbons (BATH) was determined using three aliphatic (Chloroform, n-Hexane and n-Octane) and two aromatic (Toluene and Xylene) solvents. Maximum affinity of Lactobacillus strains towards chloroform and toluene indicated the presence of low electron acceptor/ acidic surface components on cell surface of most of the strains. The highest value of per cent hydrophobicity was recorded with chloroform in HM1 (L. casei) (97·10 ± 3·35%) and LGG (98·92 ± 1·24%). A moderate auto-aggregation attribute was observed in all of our Lactobacillus isolates. Only HM10, HM12 and HM13 exhibited comparatively enhanced precipitation rate after 7 h of incubation period. The adhesion potential to collagen matrix was highest in LGG (26·94 ± 5·83%), followed by HM1 (11·07 ± 3·54%) and HM9 (10·85 ± 1·74%) whereas, on HT-29 cells, HM8 (14·99 ± 3·61%), HM3 (13·73 ± 1·14%) and HM1 (11·21 ± 3·18%) could adhere effectively. In this manner, we noticed that although the cell surface properties and adhesion prospective of probiotic bacteria were strain dependent, five of our isolates viz. HM1, HM3, HM8, HM9 and HM10 exhibited promising cell surface properties, which could be further targeted as indigenous probiotic.
Demand for newer, stronger, stiffer, yet lighter-weight and environmental friendly (biodegradable) materials in the fields such as automobile for non-structural applications are ever increasing. The principal reasons for using natural (cellulosic) fibers is they possess several attractive properties such their economic feasibility, enhanced sustainability, good specific mechanical properties, and desirable aspect ratio for good performance after melt-processing. Natural fiber composite materials are now being rapidly utilized in automobile industries, and they have become the forefront of research and development activity. An interesting alternative for reinforcing soft polymeric matrices with short fibers is the use of cellulose fibers which show remarkable reinforcing effects in thermoplastics such as polypropylene. The current study made an attempt to investigate the suitability of sisal fibers for automobile industry for non-structural and low-strength interior applications. In this work native sisal fibers were extracted and the effect of alkali treatment on their morphological, tensile, moisture absorption and thermal properties were studied. Scanning electron micrographs indicated roughening of the surface of the fiber strands due to the removal of the hemicellulose layer on alkali treatment. The maximum weight-gain for the composite prepared from treated fibers was 2.12 %, while that for the composite prepared from untreated fiber was 4.33 %. From the thermograms, the results indicate initial degradation for the treated fiber to have improved from 174 °C to 230 °C (56 °C shift) when compared to the untreated fiber. This fiber has competitive advantages when evaluated with other natural fibers. A polymer composite was processed from the chemically modified fiber, profiled against equivalent material systems in Ashby material property charts exhibited its suitability for light, low strength and low flexure material applications which can use a potential replacement of fibres being used currently.
A novel and efficient scheme for evaluating the work of adhesion between a liquid and a polymer-grafted surface is proposed. A set of spherically symmetric potentials are gradually inserted at the interface to separate the liquid molecules from the surface according to its shape. This method is applied to the interface between the water and the gold substrate modified by poly(ethylene glycol). We find that the work of adhesion becomes maximum at the intermediate density of grafted poly(ethylene glycol). This is attributed to penetration of the water molecules into grafted poly(ethylene glycol) and hydrophilic interaction between them.
In this paper, a multilayer CNx/TiN composite film on high-speed steel substrate was prepared by using a multi-arc assisted DC reactive magnetron sputtering system. The cross-section observations of the fracture surface reveal that the films show a pure cleavage fracture due to its super-high hardness, and the interfacial strength between the film and substrate is associates with the film thickness, i.e., 2μm is a critical thickness for the present deposition. That is to say, there is no disbonding or cracking at the interface when the film thickness is less than 2μm, while the interfacial failure is generated if the film thickness is larger than 2μm. This direct SEM observation of the fracture surface provides a distinct image for evaluating the mechanical property and also analyzing the failure mechanism of the films.
Adhesion between cells and other cells (cell–cell adhesion) or other tissue components (cell–matrix adhesion) is an intrinsically non-local phenomenon. Consequently, a number of recently developed mathematical models for cell adhesion have taken the form of non-local partial differential equations, where the non-local term arises inside a spatial derivative. The mathematical properties of such a non-local gradient term are not yet well understood. Here we use sophisticated estimation techniques to show local and global existence of classical solutions for such examples of adhesion-type models, and we provide a uniform upper bound for the solutions. Further, we discuss the significance of these results to applications in cell sorting and in cancer invasion and support the theoretical results through numerical simulations.
Polyurethane-based bioadhesive was synthesized with polyols derived from castor oil (chemically modified and unmodified) and hexamethylene diisocyanate with chitosan addition as a bioactive filler. The objective was to evaluate the effect of type of polyols with the incorporation of low-concentrations of chitosan on the mechanical and biological properties of the polymer to obtain suitable materials in the design of biomaterials. The results showed that increasing physical crosslinking increased the mechanical and adhesive properties. An in vitro cytotoxic test of polyurethanes showed cellular viability. The biocompatibility of the polyurethanes favors the adhesion of L929 cells at 6, 24, and 48 h. The polyurethanes showed bacterial inhibition depending on the polyol and percentage of chitosan. The antibacterial effect of the polyurethanes for Escherichia coli decreased 60–90% after 24 h. The mechanical and adhesive properties together with biological response in this research suggested these polyurethanes as external application tissue bioadhesives.
A new waterborne acrylic (WAC) hybrid adhesive was evaluated for an untreated polypropylene lamination. The WAC hybrid adhesive was formulated with a new class of porous clay heterostructure (PCH), which was modified with 3-(trimethoxysilyl)propyl methacrylate (as a coupling agent) to promote chemical bonding with the acrylic matrix to form a methacrylate-functionalized PCH (MPCH). The WAC hybrid adhesive was based on copolymers (2-ethylhexyl acrylate, ethylene glycol methyl ether acrylate, 2-(hydroxyethyl) methacrylate, styrene and acrylic acid) with varying amounts of MPCH. The scanning electron microscopy micrographs revealed the presence of a well dispersed MPCH distributed throughout the matrix. The optimal adhesive performance, in terms of the 180° peel strength of bonded joints, of 140.2 N/m was achieved using 1.5 wt% of MPCH, while the thermal stability of the adhesives was improved with increasing MPCH loading levels.
Recent advances in alumina ceramics are focused toward innovative processing routes to improve their mechanical reliability while retaining their superior wear resistance, which might be possible if a thin layer of dense alumina can be formed on a metallic substrate such as Ti–6Al–4V with high mechanical strength. For this purpose, we propose a new two-step process in which a dense layer of Al deposited on the Ti alloy by cold metal transfer method, formed a dense Al3Ti gradient reaction layer at their interface to improve adhesion in a single step. Subsequent micro-arc oxidation treatment transformed Al layer to a graded alumina layer in which γ-alumina decreased and α-alumina increased with increasing depth. Abrasion of outer regions revealed underlying pure α-alumina regions with high Vickers hardness matching with that of sintered alumina. The designed alumina/Ti alloy hybrid can be a potential candidate for wear resistance applications.
Human dental pulp stem cells (DPSCs) can differentiate, showing potential for regenerative medicine. Designing artificial surfaces with properties appropriate for the initiation of extracellular matrix (ECM) adsorption and organization is a critical step in tissue engineering and can greatly impact protein adhesion. Sulfonated polystyrene (SPS), used as a scaffold for tissue development, stimulates protein adsorption due to the increased negative charge of sulfonate.
Graphene and graphene oxide (GO) sheets enhance stem cell growth and differentiation because they are soft membranes with “high in-plane” stiffness and have the potential to be transferable and implantable platforms. This project functionalized GO and reduced GO (RGO) with gold or silver nanoparticles, mixing with SPS to investigate their combined impact on DPSC differentiation and protein adsorption, hypothesizing that this combination supplies more charges to better absorb the proteins to the surface and stimulate differentiation.
Results indicate that proteins of cells plated on the gold-RGO/SPS surfaces were the most highly adsorbed and most densely packed. Additionally, the cell moduli data indicated that the metal-RGO solutions substantially induced a change in modulus even more than Dexamethasone, a glucocortoid known to enhance this process in DPSCs. This suggests that the metal-RGO solutions may be instrumental in osteogenic induction.
Given the lack of satisfying treatments for consolidating marble affected by thermally induced grain detachment (the so-called "sugaring"), the use of aqueous solutions of diammonium hydrogen phosphate (DAP) has recently been proposed. The idea is to form a new binding mineral (hydroxyapatite, HAP) as the reaction product between the DAP solution and the calcitic substrate. In this study, we investigated the effects of adding small quantities of ethanol (EtOH) to the DAP solution, with the aim of favoring HAP formation. The results of the study indicate that, when a 0.1 M DAP and 0.1 mM CaCl2 solution in 10 vol% EtOH is used, complete coverage of marble surface with a crack-free coating with reduced porosity is achieved (whereas no coating is formed without EtOH addition). This is thought to be a consequence of the weakening of hydration shells of phosphate ions in the DAP solution, thanks to the presence of ethanol molecules. When used to restore mechanical properties of weathered marble, the treatment with 10 vol% EtOH was found to significantly improve the dynamic elastic modulus after a single application and to completely restore it after a second application.
Mechanical integrity of the interfacial region between ceramic coatings and substrates is critical to high performance coated mechanical components and manufacturing tools. Mechanical failure of the coating/substrate interfacial region often leads to catastrophic failure of the coated system as a whole. Despite extensive research over the past two decades, quantitative assessment of the mechanical response of coating/substrate interfacial regions remains a challenge. The lack of reliable protocols for measuring the mechanical response of coating/substrate interfacial regions quantitatively hampers the understanding of key factors controlling the mechanical integrity of coating/substrate interfaces. In this paper, we describe a new micro-pillar testing protocol for quantitative measurement of critical stresses for inducing shear failure of interfacial regions in ceramic-coating/metal-adhesion-layer/substrate systems. We observe significant differences in the critical stress for shear failure of interfacial regions in CrN/Cu/Si, CrN/Cr/Si, and CrN/Ti/Si systems. The present testing protocol has general applicability to a wide range of coating/interlayer/substrate systems.
Nanoindentation testing of compliant materials has recently attracted substantial attention. However, nanoindentation is not readily applicable to softer materials, as numerous challenges remain to be overcome. One key concern is the significant effect of adhesion between the indenter tip and the sample, leading to larger contact areas and higher contact stiffness for a given applied force relative to the Hertz model. Although the nano-Johnson–Kendall–Roberts (JKR) force curve method has demonstrated its capabilities to correct for errors due to adhesion, it has not been widely adopted, mainly because it works only with perfectly spherical tips. In this paper, we successfully extend the nano-JKR force curve method to include Berkovich and flat indenter tips by conducting numerical simulations in which the adhesive interactions are represented by an interaction potential and the surface deformations are coupled by using half-space Green’s functions discretized on the surface.
In this study, three types of graphene films—hydrothermal reduced graphene oxide (GO) film, thermal reduced GO film, and GO film—on silicon substrate by using 3-aminopropyl triethoxysilane (APTES) as the interface adhesive layer were prepared for investigation. The chemical compositions of the samples were characterized by x-ray photoelectron spectroscopy (XPS). Surface morphologies, adhesive forces, and nano friction forces in air and aqueous solutions with different pH values were investigated by atomic force microscopy (AFM). Results showed that capillary force dominated the adhesive force in air condition, and adhesive force was much smaller in aqueous solution than in air due to the disappearance of the capillary force. Adhesive force and friction coefficient of the three samples slightly decreased with the increase of pH values. Hydrothermal reduced GO film exhibits the best lubricity both in air and in liquids among those three films.