Higher Work Of Adhesion Research Articles

Plasma effect on polyhydrosilane/metal interfacial adhesion/cohesion interactions

Interactions between a polyhydrosilane film and some metals – gold, silver, aluminum – were theoretically estimated from the work of spreading. This parameter was calculated from disperse and polar components of surface tension corresponding to the polymer and metal. The polyhydrosilane surface properties were experimentally determined from contact angle measurements introduced in the Fowkes relation. To enhance the polymer/metal compatibility, nitrogen plasma exposure was applied, revealing that after this treatment the cohesion interactions are lower than the adhesion ones. An increase in surface polarity was reflected in a higher work of adhesion between metal and polymer substrates, particularly with gold. To confirm the theoretical results regarding the adhesion properties, an atomic force microscopy experimental method was applied in order to determine the adhesion between a gold covered tip and a polyhydrosilane film surface. These results are essential for optimizing polymer surface features for designing reliable electronic components.

Gas discharge plasma treatment of poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) for enhanced paint adhesion

Low-energy hydrogen-ions and tetrafluoromethane-ions produced from a gas discharge ion source were irradiated to poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) (PETG) sheets for enhancing paint adhesion. The ion beams were characterized using a cast steel mass spectrometer, while the untreated and treated samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, contact angle measurements, and profilometry. The paint adhesion was determined by using the standard method for evaluating adhesion by knife [ASTM D6677-07, Standard Test Method for Evaluating Adhesion by Knife (ASTM International, West Conshohocken, PA, 2012)] and was correlated with the calculation of the work of adhesion derived from the Young–Dupré equation. After plasma treatment, a significant decrease in the contact angle was observed in all samples, except for the CF4 ion-treated samples with the discharge current of 3 mA and an irradiation time of 30 min. At longer irradiation times, the treated samples showed lesser changes in the contact angle measurement. The increase in the average and root-mean-square surface roughness was observed on the samples after plasma treatment. The samples treated with either H2 or CF4 ions for 15 min showed a direct correlation between the discharge current and surface roughness. The samples treated for 30 min showed no significant correlation between the surface roughness and discharge current, which can be attributed to the possible melting of the samples since PETG has a low melting point. The observation made in this study on the relationship of wettability and surface roughness is consistent with the Wenzel wetting mode. Scanning electron micrographs showed surface etching on the hydrogen ion-treated samples while no significant surface changes were observed for the CF4 ion-treated samples. In general, paint adhesion was stronger for samples that exhibited enhanced wettability and high work of adhesion. The optimal work of adhesion to double the paint adhesion performance was at least 84.79 mN/m. The increase in the surface roughness after the treatment provided an increased friction between the paint and the PETG surface. The increase in the paint adhesion was also due to the covalent, hydrogen, and van der Waals bonding that are typically observed for highly wettable surfaces.

Electric and adhesion properties of an interface between Sn1 − x Mn x Te single crystals and Bi–Sn alloys

The adhesion and electric properties of an interface between Sn1 − xMnxTe single crystals and a 57 wt % Bi and 43 wt % Sn alloy in a temperature range of ∼77–300 K are studied. It is shown that the Bi–Sn alloy and the above single crystals form an ohmic contact that exhibits fairly high work of adhesion and strength of adhesion, along with low contact resistance. The deposition of the Bi–Sn alloy on the end faces of the crystals results in the formation of such intermediate phases as Bi2Te3 and SnTe at the interface, the doping of the near-contact region of the crystal, and the filling of vacancies in the tin sublattice in this region with diffusing atoms of the contact alloy components.

Molecular adhesion at clay nanocomposite interfaces depends on counterion hydration-molecular dynamics simulation of montmorillonite/xyloglucan.

Nacre-mimetic clay/polymer nanocomposites with clay platelet orientation parallel to the film surface show interesting gas barrier and mechanical properties. In moist conditions, interfacial adhesion is lowered and mechanical properties are reduced. Molecular dynamic simulations (MD) have been performed to investigate the effects of counterions on molecular adhesion at montmorillonite clay (Mnt)-xyloglucan (XG) interfaces. We focus on the role of monovalent cations K(+), Na(+), and Li(+) and the divalent cation Ca(2+) for mediating and stabilizing the Mnt/XG complex formation. The conformation of adsorbed XG is strongly influenced by the choice of counterion and so is the simulated work of adhesion. Free energy profiles that are used to estimate molecular adhesion show stronger interaction between XG and clay in the monovalent cation system than in divalent cation system, following a decreasing order of K-Mnt, Na-Mnt, Li-Mnt, and Ca-Mnt. The Mnt clay hydrates differently in the presence of different counterions, leading to a chemical potential of water that is highest in the case of K-Mnt, followed by Na-Mnt and Li-Mnt, and lowest in the case of Ca-Mnt. This means that water is most easily displaced from the interface in the case of K-Mnt, which contributes to the relatively high work of adhesion. In all systems, the penalty of replacing polymer with water at the interface gives a positive contribution to the work of adhesion of between 19 and 35%. Our work confirms the important role of counterions in mediating the adsorption of biopolymer XG to Mnt clays and predicts potassium or sodium as the best choice of counterions for a Mnt-based biocomposite design.

Adhesion anisotropy between contacting electrospun fibers.

The mechanical properties of electrospun fiber networks are critical in a range of applications from filtration to tissue engineering and are dependent on the adhesion between contacting fibers within the network. This adhesion is complex as electrospun networks exhibit a variety of contacts, including both cross-cylinder and parallel fiber configurations. In situ atomic force microscopy (AFM) was used to quantify the work of adhesion between a pair of individual electrospun polyamide fibers using controlled orientations and measurable contact areas. The work of adhesion was found to depend strongly on the fiber-fiber contact, with the separation of fibers in a parallel fiber configuration exhibiting considerably higher work of adhesion across a range of contact lengths than a cross-cylinder configuration. Our work therefore highlights direction-dependent adhesion behavior between electrospun fibers due to a suggested polymer chain orientation mechanism which increases net van der Waals interactions and indicates the variability of adhesion within a random electrospun fiber network.

Wetting behaviour and interfacial microstructure of Sn–Ag–Zn solder alloys on nickel coated aluminium substrates

Wetting behaviours of two lead free solders (Sn–2·625Ag–2·25Zn and Sn–1·75Ag–4·5Zn) on nickel coated aluminium substrates were investigated. Sn–2·625Ag–2·25Zn exhibited better wettability compared to Sn–1·75Ag–4·5Zn solder. Contact angles of the solders increased with increasing roughness of the substrate. The Young–Dupre equation was used to evaluate the work of adhesion of solder on the substrate. Sn–2·625Ag–2·25Zn solder exhibited higher work of adhesion than Sn–1·75Ag–4·5Zn. A thin continuous layer of Ni3Sn was detected at the interface between Sn–2·625Ag–2·25Zn solder and nickel coated Al substrate. Sn–1·75Ag–4·5Zn solder exhibited scallop intermetallic compounds (IMCs) growing into the solder field as well as a thin continuous IMC in some cases. Ni3Sn and Ni3Sn4 IMCs were observed at the interface of Sn–1·75Ag–4·5Zn solder and nickel coated Al.

Surface properties and bond strength measurements of N-vinylcaprolactam (NVC)-containing glass-ionomer cements

N-vinylcaprolactam (NVC)-containing glass ionomers are promising dental restorative materials with improved mechanical properties; however, little information is available on other physical characteristics of these types of modified glass ionomers, especially their surface properties. Understanding the surface characteristics and behavior of glass ionomers is important for understanding their clinical behavior and predictability as dental restorative materials. The purpose of this study was to investigate the effect of NVC-containing terpolymers on the surface properties and bond strength to dentin of GIC (glass-ionomer cement), and to evaluate the effect of NVC-containing terpolymer as a dentin conditioner. The terpolymer of acrylic acid (AA)-itaconic acid (IA)-N-vinylcaprolactam (NVC) with a molar ratio of 8:1:1 (AA:IA:NVC) was synthesized by free radical polymerization and characterized using nuclear magnetic resonance ((1)H-NMR) and Fourier transform infrared spectroscopy (FTIR). The synthesized terpolymer was used in glass-ionomer cement formulations (Fuji IX GP). Ten disc-shaped specimens (12 × 1 mm) were mixed and fabricated at room temperature. Surface properties (wettability) of modified cements were studied by contact angle measurements as a function of time. Work of adhesion values of different surfaces were also determined. The effect of NVC-modified polyacid on the bond strength of glass-ionomer cement to dentin was investigated. The mean data obtained from contact angle and bonding strength measurements were subjected to t test and 2-way ANOVA (α=.05). NVC-modified glass-ionomer cements showed significantly (P<.05) lower contact angles (46 degrees) and higher work of adhesion (W(A)=60.33 erg/cm(2)) in comparison to commercially available Fuji IX GP (57 degrees and W(A)=53.01 erg/cm(2)). The wettability of dentin surfaces conditioned with NVC-containing terpolymer was significantly higher (P<.05) (22 degrees, WA=73.77 erg/cm(2)) than dentin conditioned with GC dentin conditioner (29 degrees, W(A)=70.52 erg/cm(2)). The experimental cement also showed significantly higher values for shear bond strength to dentin (8.7 ±0.15 MPa after 1 month) when compared to the control group (8.4 ±0.13 MPa after 1 month). NVC-containing terpolymers may enhance the surface properties of GICs and increase their bond strength to the dentin. Furthermore, NVC-containing polyelectrolytes are better dentin conditioners than a commercially available dentin conditioner (GC dentin conditioner).

Effects of N-vinylpyrrolidone (NVP) containing polyelectrolytes on surface properties of conventional glass-ionomer cements (GIC)

It has been found that polyacids containing an N-vinylpyrrolidinone (NVP) comonomer produces a glass inomer cement with improved mechanical and handling properties. The objective of this study was to investigate the effect of NVP modified polyelectrolytes on the surface properties and shear bond strength to dentin of glass ionomer cements. Poly(acrylic acid (AA)-co-itaconic acid (IA)-co-N-vinylpyrrolidone) was synthesized by free radical polymerization. The terpolymer was characterized using 1H NMR, FTIR spectroscopy and viscometry for solution properties. The synthesized polymers were used in glass ionomer cement formulations (Fuji II commercial GIC). Surface properties (wettability) of modified cements were studied by water contact angle measurements as a function of time. Work of adhesion values of different surfaces was also determined. The effect of NVP modified polyacid, on bond strength of glass-ionomer cement to dentin was also investigated. The mean data obtained from contact angle and bonding strength measurements were subjected to one- and two-way analysis of variance (ANOVA) at α = 0.05. Results showed that NVP modified glass ionomer cements showed significantly lower contact angles ( θ = 47°) and higher work of adhesion (WA = 59.4 erg/cm 2) in comparison to commercially available Fuji II GIC ( θ = 60° and WA = 50.3 erg/cm 2, respectively). The wettability of dentin surfaces conditioned with NVP containing terpolymer was higher ( θ = 21°, WA = 74.2 erg/cm 2) than dentin conditioned with Fuji conditioner ( θ = 30°, WA = 69 erg/cm 2). The experimental cement also showed higher but not statistically significant values for shear bond strength to dentin (7.8 MPa), when compared to control group (7.3 MPa). It was concluded that NVP containing polyelectrolytes are better dentin conditioners than the commercially available dentin conditioner (Fuji Cavity Conditioner, GC). NVP containing terpolymers can enhance the surface properties of GICs and also increase their bond strength to the dentin.

Physicochemical processes at the boundary between some semiconducting solid solutions and contact alloys

Some adhesion and electric properties of boundaries between Bi2Te3-Sb2Te3-Gd2Te3 solid solution crystals and Bi-Pb-Sn and Bi-Sn alloys and the formation of various intermediate phases in these systems were studied. When the alloys are applied to crystal end faces, crystals are dissolved in contact material melt and contact material components diffuse into crystals. This is accompanied by the formation of intermediate phases such as PbTe and SbTe at the boundary. The 57 wt % Bi + 43 wt % Sn alloy was found to form contacts with the systems studied with fairly low contact resistances and wetting angles and high work of adhesion and adhesion strength.

Room Temperature Detachment Nanolithography Using a Rigiflex Polymeric Mold

We report on detachment nanolithography of an organic thin film at room temperature mediated by ultraviolet (UV) exposure. A nanopatterned, UV curable polyurethane acrylate (PUA) mold was placed on a spin-coated organic film made of 4,4'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) under a low pressure (1-2 bar). A higher work of adhesion at the organic/mold interface induced detachment of the contacting layer on silicon or gold substrate, resulting in well-defined nanopatterns without a residual layer. The detachment was highly improved by a short-term UV exposure, rendering the film surface free from contaminant hydrocarbons with a lower cohesive force, as confirmed by Fourier transform infrared (FTIR) spectroscopy and measurements of contact angle of water.

The effects of Zn and Mg on the mechanical properties of the Al/TiN interface: afirst-principles study

The adhesion and tensile behaviours of Zn and Mg contaminated Al/TiN(001) interfacesare investigated by first-principles calculations. The structures of the monolayer andhalf-monolayer Zn and Mg at the interface are studied. The results show that Zn and Mggreatly affect the adhesion and mechanical properties of the Al/TiN(001) interface. BothZn and Mg increase the interfacial separation and decrease interface adhesion. Duringthe tensile simulation, fractures of the Zn and Mg contaminated Al/TiN(001)interfaces are caused by the rupture of interface Zn–N and Mg–N bonds. The tensilestrengths of them are smaller than that of the clean Al/TiN(001) interface. The Mgcontaminated interfaces have higher work of adhesion and larger tensile strength than theZn contaminated ones. The calculations are consistent with the experimentalresults and provide an insight from the atomic and electronic points of view.

Estimating the Polymer−Metal Work of Adhesion from Molecular Dynamics Simulations

The thermodynamic concept used to quantify adhesion on a fundamental molecular level is the work of adhesion. However, most of the experimental techniques give no, or very limited information about its magnitude. In this paper, a way to estimate the work of adhesion for copper−(acrylonitrile-butadiene-styrene) (ABS) interface using molecular dynamics simulations is presented. The work of adhesion is calculated from the interactions between single molecules constituting the ABS polymer (poly(styrene-co-acrylonitrile) and polybutadiene molecules) and copper (oxide) surface, using their van der Waals contact area. The calculated work of adhesion seems to be independent of the number of polymer molecules present on the copper surface, monomer residue unit sequence within the polymer molecule, and the type of copper surface. Introduction of oxygen atoms to the metallic surface and the polymer molecules significantly increases the work of adhesion. The highest work of adhesion was found between the oxidized copper surface and high oxygen content copolymer poly(styrene-alt-maleic anhydride). Results are shown to qualitatively correspond to previously reported experimental observations.

Transfer fabrication technique for embedded and inverted micro/nanostructures

A transfer fabrication technique is developed to construct embedded and inverted micro/nanostructures that cannot be readily built by other methods. Transfer patterning/printing is used for the fabrication, which involves transferring a patterned layer on a flat substrate to another substrate that has a higher work of adhesion with the layer than the flat substrate. The technique is relatively simple and fast (∼10s). Inversion of a shape that is made possible by the transfer is the basic concept. This inversion allows fabrication of three-dimensional embedded structures through multiple stacking. The technique could open new avenues for various applications.

Complex Adhesion Effects of Inorganic Nanofillers vs Microfillers in Polymer Composites

AbstractThe adhesion parameters of fillers in composites, coefficient of wetting, interfacial free energy and work of adhesion, were calculated in order to evaluate the difference between the effects of selected microfillers vs nanofillers in polyacrylate (PA) and poly (vinyl acetate)(PVAc) matrix. The results showed that the improved fundamental adhesion, i.e. higher work of adhesion in nanocomposites resulted in the improved practical adhesion i.e. higher mechanical properties. The interfacial region was additionally modified by the controlled pre‐treatment of calcium carbonate micro‐ and nanofillers by sodium stearate that lowered the interactions with PVAc matrix. The composite morphological and mechanical properties changed accordingly. The lowered coefficient of interactions explained the pronounced composite failure at the interphase by dewetting and finally lead to the composite weakening. The conclusion about the complex relationship between the composite properties and engineering the interphase was confirmed.

Bioadhesive grafted starch copolymers as platforms for peroral drug delivery: a study of theophylline release

Nonirritant bioadhesive drug release systems based on starch–acrylic acid graft copolymers prepared by radiation of starch and acrylic acid mixtures with 60Co were developed for buccal application. The release rate of theophylline (TPL), used as a model drug, depended on the ratio of starch to acrylic acid and on the presence of cations in the graft copolymers, but was practically not affected by the pH (between pH 3 and 7) of the dissolution medium nor by the type of starch used (corn, rice, or potato). Possible release mechanisms are discussed for specific conditions. In general, the release behavior of the graft copolymers was found to be non-Fickian, n value being between 0.6 and 0.96, suggesting that the release was controlled by a combination of tablet erosion and the diffusion of the drug from the swollen matrix. Incorporation of divalent cations into the graft copolymers led to a significant decrease in swelling erosion of the tablets as well as a substantial retardation of drug release. Highest work of adhesion was obtained with graft copolymers containing calcium ions as well as longer time of adhesion on dogs' gingiva.

Wettability and surface charge of Si 3N 4–bioglass composites in contact with simulated physiological liquids

Wettability and surface charge studies were performed on a novel Si 3N 4–30 wt% bioglass biocomposite. Contact angle and surface tension variation with time were determined at 25°C, respectively, by the sessile and pendant drop techniques, for distinct testing liquids: water, diiodomethane, simulated body fluid (SBF) and bovine serum albumin (BSA) dissolved in SBF solution. This biocomposite revealed a hydrophilic character ( θ=26.6±2.0°) and a surface tension value (66.6 mJ m −2) comparatively higher than those of the most common bioceramics. An important characteristic is the high work of adhesion towards SBF+BSA (96.4±0.2 mJ m −2) that was measured. The Si 3N 4–bioglass material is negatively surface charged above the pH IEP=2.5 in aqueous SBF+BSA solution, as a result of the presence at the surface of unsaturated Si–O bonds and Si–OH groups. The very high negative zeta potential at pH∼7 (−58.6±5.5 mV) influenced albumin adsorption and mechanisms are discussed in terms of entropy and enthalpy gains from conformational unfolding and cations coadsorption.

Morphology and failure in nanocomposites. Part II: surface investigation

Polymer composites filled with calcium carbonate (CaCO3) nanofillers (<100 nm), and kaolin filler of layered structure, both well suited to create nanocomposites, were analysed. The aim of this study was to investigate the influence of surface properties of the filler and matrix on the adhesion parameters at the interface in composites. The inverse gas chromatography, contact angle and capillary measurements were used for the surface characterization of filler and matrix. Although these methods are based on different assumptions, we found the same trends in the effects of filler surface treatment and/or matrix chemical structure on the changes in the dispersive and polar components of the surface energy. The energetics of the filler and matrix was varied in order to investigate the work of adhesion, interfacial energy and coefficient of spreading, and their influence on the composite properties. We found that the surface treatment of calcium carbonate filler lowered the filler surface energy and the work of adhesion in the composite with poly (vinyl acetate) matrix. The mechanical, thermal and morphological properties of the composite with treated CaCO3, measured in the first part of this paper, indicated a weak and thin interphase. In the composite with kaolin filler the higher interaction with the polyacrylate copolymer matrix based on styrene as compared to the one based on methyl methacrylate, was confirmed by the higher work of adhesion in the interphase, resulting in a stronger reinforcing of the composite.

The mechanism of destruction of a-C:H films under the action of aggressive liquids

Abstract The a-C:H films were deposited on monocrystalline silicon (001) substrates from RF (13.56 MHz) discharge plasma in a capacity-type reactor. The stability of a-C:H films in different aggressive liquids was investigated by the methods of wettability and thermodesorption (TD) using a mass spectrometer to detect particles being desorbed in the temperature range 20–800°C. Comparative analysis of the data on film wettability and TD has allowed us to suggest the mechanism of a-C:H film destruction. The mechanism is based on the catalytic activity of ions in solution, which interact intensively with surface carbon atoms. The highest destabilisation of carbon bonds in the film near-surface layer, which causes film destruction to form CO2, is found to occur in contact with an alkali solution. In this case the CO2 ion flow intensity is two orders of magnitude higher than that from the initial film surface. This finding corresponds to the best wettability (wetting angle θ=10–12°) and the highest work of adhesion (Wa=158.5 mJ/m2) of alkali solution to a-C:H film surface. The replacement of hydrogen by nitrogen in the film structure increases its chemical stability when contacting with aggressive media.

Adsorption of proteins to surfaces in seawater

Adsorption of two proteins, bovine serum albumin and ribulose-1,5-bisphosphate carboxylase, (RuBPcase), onto a variety of surfaces was examined. Protein adsorption was rapid, but was irreversible in seawater only when bulk protein concentrations were low (<10 μg ml −1). Adsorption was consistently higher onto Parafilm (a surface with a low work of adhesion and high hydrophobicity) than onto glass (high work of adhesion and low hydrophobicity). When a variety of surfaces were tested, there was a significant negative relationship between RuBPcase adsorption and work of adhesion. For all surfaces, adsorption was higher in seawater than in low ionic strength buffer. The high adsorption in seawater was a result of the high salt concentration of seawater. Low concentrations of both NaCl and MgCl 2 increased adsorption, but MgCl 2, was more effective. The relationship between work of adhesion and adsorption indicates that hydrophobic interactions are important in determining protein adsorption, especially at high salinities.