Adhesion and friction studies on silicon dioxide nanoparticle-textured surfaces prepared by the spin-coating process

Silicon dioxide nanoparticle-textured surfaces were prepared by the spin-coating process. The adhesion and friction properties of the nanoparticle-textured surfaces were investigated using an atomic force microscope colloidal probe. Experimental results revealed that the nanoparticle-textured surfaces can significantly reduce adhesive and friction forces compared with a flat surface. The main reason for this phenomenon was that the nanotexture can reduce contact area between the sample surface and the colloidal probe. The relationships between surface root mean square (RMS) roughness, packing density, and spinning rate were also discussed. The effects of surface RMS roughness and packing density on the adhesion and friction behaviors of the nanotextured surfaces were investigated. The adhesive and friction forces of the nanoparticle-textured surfaces decreased with increasing packing density. The friction forces of the nanoparticle-textured surfaces increased with increasing applied load and sliding velocity. This approach should be applied to new developments in nanosystems to reduce adhesive and friction forces between contact pairs.     

Simulation of the attachment system with various tip shapes contacting rough surface

In this paper, we investigate the effects of various contact shapes on the adhesion performance for the attachment system contacting rough surfaces. Four different tip shapes of sphere, flat punch, torus and tape are considered. We demonstrate the effect of the tip size and the elastic modulus on the adhesion force through the adhesion analysis for single tips with four different shapes. In order to investigate an effect of tip shape on adhesion performance for the attachment system contacting rough surface with different σ values, single level attachment system was simulated. The attachment system is modeled from the geometrical size of spatulae of Tokay gecko. The effect of tip shape on the adhesion enhancement and how far its effect can be reached for the surface roughness are investigated. It is shown that the effect of tip shape on the adhesion enhancement is limited to the surface roughness with smaller than several micrometers and further adhesion enhancement can not be expected at rougher surfaces.     

Direct adhesion measurements of pharmaceutical particles to gelatin capsule surfaces

Scanning probe microscopy (SPM) was used to measure directly the adhesion of individual lactose particles to the surface of gelatin capsules employed in dry powder inhalant drug delivery systems. In this study, SPM shows that gelatin capsule surfaces with high surface heterogeneity and high-contrast friction exhibit high adhesion and that gelatin capsule surfaces with low surface heterogeneity and low-contrast friction exhibit low adhesion. The adhesion of lactose particles to gelatin capsules was also determined by measuring the retention of lactose particles in the capsules. The adhesion trend obtained with individual lactose particles using the colloidal probe technique agrees with the macroscopic retention results. The adhesion appears to be proportional to the particle size for homogeneous capsule surfaces. In dry powder inhalation products, the Lifshitz-van der Waals forces and acid-base interactions appear to be the principal forces contributing to particle-surface adhesion. The physicochemical nature of the capsule surface seems to dictate the spatial variation of adhesion across the surface. The SPM results clearly show that the surface physicochemical properties depend on the gelatin and mold release agent utilized in the manufacture of gelatin capsules. One of the practical implications of this study is that extraneous surface contamination of gelatin capsules by chemical processing aids such as mold release agents appears to be a key factor affecting the respirable fraction in dry powder inhalation products.     

Characterization and adhesion testing of mixed silane-treated surfaces

Single silanes have been well studied as adhesion promoters, but there are areas of improvement that could use the properties of an additional silane. This research examines the combination of an adhesion promoter with a second silane of different chemical functionality in order, to increase the number of potential applications. Several techniques are investigated for producing mixed silane layers, including solution deposition, microcontact printing and vapor deposition. The second goal of this research is to determine the adhesion between polymers and heterogeneous micropatterned silanes. The two silanes used are n-octadecyltrichlorosilane (ODTS) and 3-aminopropyltriethoxysilane (APS). APS is an adhesion promoter between most polymers and oxide surfaces, while ODTS is very hydrophobic and has insignificant adhesion to polymers. Surfaces are characterized with an Atomic Force Microscope (AFM) with Pulsed Force Mode (PFM), allowing simultaneous topography, adhesion and stiffness measurements of the surface to be generated. In a 180°-peel test between poly(vinyl butyral) (PVB) and glass, the addition of ODTS results in the decrease of the surface energy and a dramatic decrease in adhesion. In a wedge test, the adhesion of APS is found to be proportional to the percent coverage.     

Peeling of PSAs on Viscoelastic Substrates: A Failure Criterion

This work deals with the study of the viscoelastic and adherence properties of pressure-sensitive adhesive (PSA) formulations dedicated to medical applications. We have developed a specific viscoelastic substrate to measure the adherence properties of PSAs that mimics adhesion on human skin. In the present article, we describe several experiments dedicated to a better understanding of adhesion on viscoelastic substrates without discussing specifically the case of human skin. In this way, we have studied different model adhesive formulations based on real medical formulations, and we have related the rheological behavior to the adherence properties obtained on different substrates to study the various specific effects due to the viscoelasticity of soft substrates. We propose from this study a failure criterion that allows one to derive a reasonable estimate of the peeling transition rate from cohesive to interfacial or stick-slip failure.     

Peeling of PSAs on Viscoelastic Substrates: A Failure Criterion

This work deals with the study of the viscoelastic and adherence properties of pressure-sensitive adhesive (PSA) formulations dedicated to medical applications. We have developed a specific viscoelastic substrate to measure the adherence properties of PSAs that mimics adhesion on human skin. In the present article, we describe several experiments dedicated to a better understanding of adhesion on viscoelastic substrates without discussing specifically the case of human skin. In this way, we have studied different model adhesive formulations based on real medical formulations, and we have related the rheological behavior to the adherence properties obtained on different substrates to study the various specific effects due to the viscoelasticity of soft substrates. We propose from this study a failure criterion that allows one to derive a reasonable estimate of the peeling transition rate from cohesive to interfacial or stick–slip failure.     

Aunps and Agμps-functionalized zirconia surfaces by hybrid laser technology for dental implants

This work presents innovative zirconia surfaces functionalized with gold nanoparticles (Aunps) and silver microparticles (Agμps) through versatile laser technology where laser parameters and subtractive/additive strategies were combined to apply in dental implant surfaces regarding antibacterial potentialities. Au_nps-functionalized zirconia surfaces were produced by a hybrid process starting with nanoparticles production by Nd:YAG laser ablation, followed by its deposition through spray system and its adhesion to the zirconia surface by the laser CO₂ action, varying laser power and scan speed parameters. Ag_μps-functionalized zirconia surfaces were obtained through a hybrid laser process starting by laser texturing of the compacted zirconia surface, followed by allocation of Ag powder into the texture and its subsequent laser sintering, varying laser power. The functionalized zirconia surfaces were analyzed through SEM/EDS. In order to mimic the implant screwing effect, the samples were subjected to reciprocating friction tests against bone. It allows to evaluate the adhesion of the zirconia surface to the bone and the resistance to surface detachment. A purple colloidal solution of spherical gold nanoparticles with an average size of 5 ± 3 nm was successfully produced by laser. The friction tests revealed a good behavior of both functionalized zirconia surfaces indicating that their integrity is not affected during implant screwing insertion. A good dispersion of nanoparticles on the zirconia surface was observed indicating that the spray system is an effective way to deposit nanoparticles on the surface. A high amount of agglomerates was found for samples where low laser power (P = 11W) and scan speed (v = 1000 mm/s) were applied, probably due to the high density of energy (E). A decrease of defects on the sintered Ag layer with increasing laser power from 3 to 6 W was found, mainly related with the amount of laser energy density. The ion release showed to be strongly dependent on particle size.     

Friction and wear of metals in contact with pyrolytic graphite

Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments including, vacuum, oxygen, water vapor, nitrogen and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. LEED, Auger spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.     

Poly(dopamine) assisted deposition of adherent PPy film on Ti substrate

This study aims to address an issue to a subject that is still less present in literature: the adherence of polypyrrole (PPy) films on bioinert substrate. The poly(dopamine) (PDA) assisted deposition of PPy film on titanium substrate was performed in two steps. The chemical self-polymerization of dopamine was performed as a preliminary step from dopamine in Tris buffer solution on titanium substrate. Then, the resulted poly(dopamine) layer consisting of anchors with strong interactions with Ti surface was a new suitable substrate for polypyrrole film electrochemical deposition. The new PDA–PPy films were characterized in terms of interest properties for the desired biomedical applications: adherence, electrochemical stability of PDA–PPy film, wettability, topography, morphology and antibacterial effect. The poly(dopamine) assisted deposition of PPy film has been shown to be a facile and efficient route to improve the adhesion of PPy film on titanium maintaining or improving the properties of polymeric film.     

The Effect of Silane Surface Treatment of Carbon Fiber on the Tribological Properties of Bismaleimide(BMI) Composite

Silane surface modification method was used for the surface treatment of carbon fiber to improve the interfacial adhesion of the carbon fiber reinforced bismaleimide(BMI) composite. The surface characteristics of untreated and treated carbon fiber were characterized by Fourier transform infrared (FT-IR) spectroscope. The friction and wear properties of the BMI composites filled with differently surface treated carbon fibers(20 vol%), were investigated on a ring-on-block tribometer. Experimental results revealed that silane treatment largely reduced the friction and wear of CF/BMI composites. Scanning electron microscope (SEM) of worn surfaces of BMI composites showed that surface treated CF/BMI composite had the strongest interfacial adhesion.     

类金刚石薄膜在人工关节摩擦副表面改性进展

类金刚石（DLC）薄膜由于其优异的减摩耐磨性以及良好的生物相容性被引入到人工关节材质中。该文综述了DLC薄膜在人工关节摩擦副表面改性的研究现状,包括DLC薄膜的分类和制备方法。尽管该薄膜已被研究数十年,但在人体复杂的生理力学环境中高负荷摩擦腐蚀等综合作用下,仍存在高内应力导致结合力不足,从而限制其在人工关节领域的应用。该文介绍了降低DLC薄膜内应力提高膜基结合力的方法和DLC薄膜生物相容性的研究进展。最后,对不同DLC薄膜人工关节摩擦副的研究进展进行了阐述。根据该综述,提出厚的无氢DLC涂层（高sp3含量）,且在两个滑动表面上均有DLC薄膜的人工关节副具有优异的耐磨性,对于承重植入体应用至关重要。     

Adhesion Mechanisms at Amine-Cured Epoxy/Aluminium Interfaces

Because the structure and the chemical composition of the interface can have a large effect on the adhesion properties of polymeric materials to metallic surfaces, many investigations have concentrated on the study of the interphase region. However, the complexity of the materials often leads to the use of model compounds to mimic the interfacial reaction. We have presented a critical discussion of three different approaches which have been used to understand the adhesion mechanism at amine-cured epoxy/aluminium interfaces: i) fracture of “real world” joints; ii) deposition of model (amino-alcohol) molecules on “real world” substrates; i) deposition of model (amino-alcohol) molecules on clean, oxidised and hydroxylated Al (100) surfaces. We have shown that model compounds can adequately duplicate the interface chemistry observed in “real world” joints. However, a detailed understanding of the exact nature of the interactions and of the role of the different reactive sites can only be achieved through studies performed on a model surface under controlled ultrahigh vacuum conditions.     

An efficient approach to control the morphology and the adhesion properties of anodized TiO2 nanotube arrays for improved photoconversion efficiency

We investigate an efficient approach to control the surface morphology and the geometrical parameter of TiO₂ nanotubes, while improving its adhesion to underlying titanium substrate, which is the key to successful fabrication of electro-optical devices. By controlling the water content and using the previously used electrolyte, nanotube arrays with surface morphology, geometrical parameters and adhesion properties relevant to required applications can be achieved. On the basis of these results, a mechanism of chemical dissolution rate is discussed in detail, in particular, with respect to the variation of nanotube length, presence of surface aggregation on the top surface, and the adhesion of nanotubes to underlying titanium substrate. It is found that the enhanced chemical dissolution rate can help to dissolve off the surface aggregation parts and reduce the internal stress at the barrier layer–metal interface. As a result this adhesion characteristic between the nanotubes and the underlying metal layer can be significantly improved. The contrastive photoelectrochemical experiments suggested that the photoconversion efficiency greatly depends on the geometric roughness factor of nanotubes and its adhesion to underlying metal layer. It shows that the 3.0% water content in previously used electrolytes has a combinative advantage to meet the optimal condition of photoconversion efficiency.     

Formation of epoxy-diamine/metal interphases

Epoxy-diamine networks are extensively used as adhesives or paints in many industrial applications. When the precursors are applied onto metallic substrates and cured, an interphase, having chemical, physical and mechanical properties quite different from that of bulk polymer, is created between the substrate and the polymer. Moreover, chemical reactions between diamine and metallic surfaces induce an increase in the practical adhesion (adherence). When the same epoxy-diamine mixtures are applied onto gold coated or polyethylene substrates, the interphase properties are the same as bulk ones. When epoxy-diamine mixtures are applied onto aluminum or titanium alloy surfaces, the glass transition temperature, amine and epoxy reaction extent, the interphase thickness, residual stresses within the interphase, Young's modulus of the interphase all depend on the amine nature (aromatic, aliphatic or cycloaliphatic), the stoichiometric ratio, the processing conditions (time and temperature), the organic layer thickness and the metallic surface treatment. Coating analyses (FTIR, FTNIR, DSC, DMTA, H⁺ and C¹³ NMR, SEC, ICP and POM) suggest that diamine monomers chemically react with and dissolve the metallic hydrated oxide layer. Then, metallic ions diffuse through the organic layer to form a complex by coordination with diamine monomers (chelate or ligand). Metal–diamine complexes are insoluble, at room temperature, both in diamine as well as in DGEBA monomers and they induce a phase separation during the curing cycle of the epoxy-diamine precursors. Furthermore, the chemical bonding of diamine monomers to the metallic surfaces and the diamine–metal crystal orientation parallel to the metallic surface within the interphase lead to chemical, physical and mechanical properties to the epoxy-diamine network which are different from those of the bulk.     

Effects of flow and geometrical parameters on the collection efficiency in cyclone separators

A mathematical model has been developed for calculation of cut-off size and fractional efficiencies in cyclone separators, by taking into account the effects of flow, particle and geometrical parameters, and acceleration assuming that the mixture of fluid and particles is homogenous, and acceleration diminishes depending on the friction and geometry. Collection efficiency curves and cut-off size values predicted by the proposed model showed a good agreement with experiments over a wide range of inlet velocities for different types of cyclones. Comparison of the obtained results with semi empirical models available in literature also indicated that the present model may be used successfully for determination of the performance of a tangential inlet cyclone. Analyses of the effects of various parameters reveals that, in addition to flow and geometrical parameters, surface friction, vortex length and flow regimes play an important role on cyclone performance especially in small cyclones.     

Effect of picosecond laser texturing on the friction behavior of silicon carbide in hybrid ceramic bearings under dry and water lubrication

Hybrid ceramic bearings consisting of silicon carbide (SiC) and GCr15 steel have a wide range of applications. However, under unlubricated and water lubricated conditions, friction between SiC and GCr15 steel inevitably occurs due to interfacial contact (e.g. dry friction and boundary friction). Laser surface texturing, as a promising surface modification technique, has a significant impact on the material friction and wear characteristics aspects. In this paper, the UV picosecond laser was used to process a groove-textured structure on the surface of silicon carbide ceramics with the aim of comparatively investigating the effect of frictional properties of textured SiC surfaces and untextured SiC surfaces under dry friction and water lubrication conditions. The results showed that the picosecond laser successfully machined surface textures on the hard-to-process SiC surface, and the picosecond laser texturing had a significant effect on the tribological behavior of SiC ceramics. Under dry friction conditions, the coefficient of friction (COF) of picosecond laser-textured SiC with GCr15 steel increased (from 0.249 to 0.296) due to the micro-cutting effect and high surface roughness caused by the texture. In contrast, the COF of picosecond laser-textured SiC with GCr15 was significantly reduced under water-lubricated conditions (from 0.22 to 0.167), due to the facilitated frictional chemical reaction on the laser-textured surface, which favors the improved tribological properties of the silicon carbide friction interface.     

AFM adhesion force measurements on conversion-coated EN AW-6082-T6 aluminium

Atomic force microscopy (AFM) has been used to measure the adhesion force between functionalised AFM tips and smooth surfaces of an EN AW-6082-T6 aluminium alloy, both before and after application of different conversion coatings. In addition, the surface of a sapphire sample was studied as a model aluminium surface. The results obtained for the sapphire surface were highly reproducible, and were used as a mean to establish proper routines for the more complex industrial surfaces. The adhesion force between a chromate conversion-coated (CCC) EN AW-6082-T6 aluminium alloy and a COOH functionalised tip was significantly increased compared to the uncoated surface, probably as a result of strong hydrogen bonding. However, the adhesion force decreased with time during the first 24 h after treatment due to aging of the CCC. Chromate-free Ti–Zr-based treatment also increased the adhesion, but the adhesion force varied significantly due to non-uniform deposition and composition of the conversion coating. The measured AFM adhesion forces correlated qualitatively with macroscopic adhesion test results obtained previously for these specific conversion coatings. The AFM technique may thus provide useful information on the adhesion behaviour of heterogeneous conversion-coated aluminium surfaces.     

Using Knock-Out Mutants to Investigate the Adhesion of Staphylococcus aureus to Abiotic Surfaces

The adhesion of Staphylococcus aureus to abiotic surfaces is crucial for establishing device-related infections. With a high number of single-cell force spectroscopy measurements with genetically modified S. aureus cells, this study provides insights into the adhesion process of the pathogen to abiotic surfaces of different wettability. Our results show that S. aureus utilizes different cell wall molecules and interaction mechanisms when binding to hydrophobic and hydrophilic surfaces. We found that covalently bound cell wall proteins strongly interact with hydrophobic substrates, while their contribution to the overall adhesion force is smaller on hydrophilic substrates. Teichoic acids promote adhesion to hydrophobic surfaces as well as to hydrophilic surfaces. This, however, is to a lesser extent. An interplay of electrostatic effects of charges and protein composition on bacterial surfaces is predominant on hydrophilic surfaces, while it is overshadowed on hydrophobic surfaces by the influence of the high number of binding proteins. Our results can help to design new models of bacterial adhesion and may be used to interpret the adhesion of other microorganisms with similar surface properties.     

The effect of irradiation surface treatment of UHMWPE fibre on the interfacial properties of PVC composite

Irradiation surface modification method was used for the surface treatment of ultrahigh molecular weight polyethylene (UHMWPE) fibre to improve the interfacial adhesion of the UHMWPE fibre reinforced PVC composite. The surface characteristics of untreated and treated UHMWPE fibre were characterised by XPS and Fourier transform infra-red spectroscope. The friction and wear properties of the PVC composites filled with differently surface-treated UHMWPE fibres (20?vol.-%), were investigated on a ring-on-block tribometer. Experimental results revealed that irradiation treatment largely increased the mechanical properties of UHMWPE fibre/neoprene/PVC (UF/N/PVC) composites. Scanning electron microscope investigation of worn surfaces of PVC composites showed that surface-treated UF/N/PVC composite had the strongest interfacial adhesion.     

Robust Non-Wetting PTFE Surfaces by Femtosecond Laser Machining

Nature shows many examples of surfaces with extraordinary wettability, which can often be associated with particular air-trapping surface patterns. Here, robust non-wetting surfaces have been created by femtosecond laser ablation of polytetrafluoroethylene (PTFE). The laser-created surface structure resembles a forest of entangled fibers, which support structural superhydrophobicity even when the surface chemistry is changed by gold coating. SEM analysis showed that the degree of entanglement of hairs and the depth of the forest pattern correlates positively with accumulated laser fluence and can thus be influenced by altering various laser process parameters. The resulting fibrous surfaces exhibit a tremendous decrease in wettability compared to smooth PTFE surfaces; droplets impacting the virgin or gold coated PTFE forest do not wet the surface but bounce off. Exploratory bioadhesion experiments showed that the surfaces are truly air-trapping and do not support cell adhesion. Therewith, the created surfaces successfully mimic biological surfaces such as insect wings with robust anti-wetting behavior and potential for antiadhesive applications. In addition, the fabrication can be carried out in one process step, and our results clearly show the insensitivity of the resulting non-wetting behavior to variations in the process parameters, both of which make it a strong candidate for industrial applications.