Effect of end‐tethered polymers on surface adhesion of glassy polymers

The adhesion between a glassy polymer melt and substrate is studied in the presence of end‐grafted chains chemically attached to the substrate surface. Extensive molecular dynamics simulations have been carried out to study the effect of the areal density ∑ of tethered chains and tensile pull velocity v on the adhesive failure mechanisms. The initial configurations are generated using a double‐bridging algorithm in which new bonds are formed across a pair of monomers equidistant from their respective free ends. This generates new chain configurations that are substantially different than the original two chains such that the systems can be equilibrated in a reasonable amount of cpu time. At the slowest tensile pull velocity studied, a crossover from chain scission to crazing is observed as the coverage increases, while for very large pull velocity, only chain scission is observed. As the coverage increases, the sections of the tethered chains pulled out from the interface form the fibrils of a craze that are strong enough to suppress chain scission, resulting in cohesive rather than adhesive failure. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 199–208, 2004     

Surface treatment of polymers by an ultraviolet laser to improve adhesion quality

The results of studies on the use of an excimer laser with a wavelength of 193 nm are presented for the treatment of surface of polymers to improve adhesion. It is shown that the radiation of coherent waves in the ultraviolet range leads to a change in surface topography and increase in its specific area, which contributes to increasing the mechanical adhesion; in addition, laser exposure activates the surface of the polymers, intensifying adsorption adhesive interaction.     

Functional microdomains of glycolipids with partially fluorinated membrane anchors: impact on cell adhesion.

Functional microdomains of glycolipids were designed by mixing neoglycolipids with partially fluorinated alkyl (F-alkyl) chains and matrix lipids with alkyl chains. Fluorescence images of the mixed lipid monolayers at the air-water interface demonstrated that it is possible to control both size and distribution of the microdomains by means of the strong demixing of alkyl and F-alkyl membrane anchors, while the carbohydrate head groups seemed to play a rather minor role. These microdomains in monolayers could be transferred onto hydrophobized substrates and subjected to experiments in a dynamic flow chamber. The results obtained here clearly indicated that the dynamic adhesion of Chinese hamster ovarial cells expressing E-selectin (CHO-E cells) on a lipid monolayer containing microdomains of sialyl Lewisx (sLex) can be both enhanced and reduced by controlled demixing of ligands and matrices. Moreover, the same clusters of sLex could also be formed in giant lipid vesicles, which can be used as a model cell that locally expresses biospecific functions.     

Surface modification of polyethylene for improving the adhesion of a highly fluorinated UV-cured coating

The surface of low density polyethylene (LDPE) was modified by grafting a photoinitiator on it, after an Ar plasma treatment. The functionalisation was characterized by contact angle measurements, XPS analyses and AFM. The grafted LDPE was then coated with a UV-curable formulation based on highly fluorinated oligomers. Although the surface tension of the coating is very low, a good adhesion onto the substrate was obtained due to the surface treatment which was applied.     

Surface modification and adhesion characteristics of polycarbonate films after graft copolymerization

The surfaces of ozone-pretreated polycarbonate films were subjected to further modification by thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrene sulfonic acid (NaSS), N,N-dimethylacrylamide (DMAA), N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-dimethyl(methacryloyl ethyl)-ammonium propanesulfonate (DMAPS) monomers. The structure and composition at the copolymer interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For polycarbonate films with a substantial amount of grafted polymer, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This microstructure was further supported by the water contact angle measurements. Adhesive-free adhesion studies revealed that the AAc, DMAA or DMAPS graft copolymerized polycarbonate film surface adhered strongly to another similarly modified surface (homo-interface) when brought into direct contact in the presence of water and subsequently dried. The development of the lap shear strength is dependent on the concentration of the surface graft, the microstructure of the grafted surface, the adhesion (drying) time, and the nature of the interfacial interaction. The simultaneous presence of chain entanglement and electrostatic interaction readily results in substantially enhanced adhesion strengths between two DMAPS graft copolymerized surfaces or between an AAc and a DMAA graft copolymerized surface (hetero-interface). XPS analyses of the delaminated surfaces suggest that failure occurred cohesively below the graft-substrate interface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 357–366, 1998     

Surface modification of PVC endotracheal tubes by oxygen glow discharge to reduce bacterial adhesion

A d.c. oxygen glow discharge was used to modify medical‐grade poly(vinyl chloride) (PVC) to study how surface chemistry and hydrophilicity influence Pseudomonas aeruginosa adhesion. The effects of plasma exposure time on the resulting surface, including chemical composition, wettability and roughness, were assessed using x‐ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy analysis. A significant alteration in the hydrophilicity of the native PVC surface was observed after oxygen glow discharge treatment. The water contact angle decreased from ～80° to 8–20°, with a weak dependence of the exposure time used. The change in surface wettability resulted from the incorporation of oxygenated functional groups, including esters, ketones and acids, as indicated by XPS analysis. The amount of oxygen incorporation was shown to be essentially independent of plasma exposure time. However, prolonged plasma exposure resulted in increased surface roughness. Bacterial adhesion efficiency was evaluated for PVC modified by 120 s of plasma exposure, because this exposure time was determined to yield the maximum decrease in contact angle. Oxygen plasma treatment of native PVC was found to yield a 70% reduction in bacterial adhesion for the four strains of Pseudomonas aeruginosa tested. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of an avidin-biotin binding system on chondrocyte adhesion and growth on biodegradable polymers

Cell adhesion to a scaffold is a prerequisite for tissue engineering. Many studies have been focused on enhancing cell adhesion to synthetic materials that are used for scaffold fabrication. In this study, we applied an avidin-biotin binding system to enhance chondrocyte adhesion to biodegradable polymers. Biotin molecules were conjugated to the cell membrane of chondrocytes, and mediated cell adhesion to avidin-coated surfaces. We demonstrated that immobilization of biotin molecules to chondrocyte surfaces enhanced cell adhesion to avidin-coated biodegradable polymers such as poly(L-lactic acid), poly(D,L-lactic acid), and polycaprolactone, compared to the adhesion of normal chondrocytes to the same type of biodegradable polymer. The biotinylated chondrocytes still maintained their proliferation ability. This study showed the promise of applying the avidin-biotin system in cartilage tissue engineering. [diagram in text].     

Surface energy of fluorinated surfaces

By fluorinating the surface of a polymer, the hydrogen bonding energy of a polar surface has been defined. The contact angles for three solvent classes; nonpolar, polar and hydrogen bonding, on a polar surface results in the separation of dispersion, polar, and hydrogen bonding energies. Both critical surface tension plots and theoretical calculations were used to define the surface energy for fluorinated polyethylene.     

An image analysis strategy to study cell adhesion

A semi-automated in situ technique has been developed for the study of the extent and kinetics of cell adhesion at the individual cell level. Our investigation involves the static sedimentation of glutaraldehyde-fixed human erythrocytes suspended in 10 mM NaCl or 10 mM NaCl containing 2% (v/v) 1-propanol onto flat, horizontal, and transparent surfaces. The surfaces used are glass, poly(ethylene terephthalate), polystyrene, and fluorinated ethylene propylene. An inverted microscope is utilized for observations. Brownian motion is used as the distinguishing criterion between adherent and non-adherent cells. The extent of adhesion is expressed as the percentage of adherent cells. Two digital image processing techniques, image averaging and image subtraction, are presented for automation of the methodology. Although all non-adherent cells undergo Brownian motion, they exhibit this behavior to varying degrees. Factors under consideration are the liquid medium's surface tension (γ_LV) and the solid substrate surface tension (γ_SV). Preliminary results reveal that, in general, variations of γ_SV and γ_LV have a statistically significant effect on the extent of adhesion at the 99% and 96% confidence levels, respectively. A time depepdence for the adhesion of populations of cells is observed. However, individual cells either instantly or gradually adhere. Image subtraction generally overestimates the number of adherent cells due to the difficulty in detection of minute oscillations. The deviation between the adhesion percentage obtained from visual observations of the monitor and image subtraction is less than 10%.     

Surface characterization of fluorinated polymers (PTFE, PVDF, PFA) for use in ultratrace analysis

Surface characterization of new unused PTFE, PFA and PVDF labware has been carried out by light microscopy, scanning electron microscopy, profilometry and atomic force microscopy. It has been found that in spite of higher micro-roughness, PFA exhibits the lowest nano-roughness and hence seems best suited as vessel material for relatively mild pressureless chemical operations for sample preparation of ultrapure substances, as container material for storage of ultrapure liquids, and for transport of such liquids, e.g., from the producer in the chemical to the end user in the microelectronics industry. This suitability refers only to the surface quality of the investigated materials. PTFE-surfaces, due to the sintering process of production, exhibit the most unfavourable surface quality of the investigated fluorinated polymers.     

Enhanced adhesion of polypropylene to copper substrates

Varying concentrations of maleic anhydride (MAH) were grafted onto three types of polypropylene (PP) in the presence of dicumyl peroxide (DCP). Pull-off adhesive strength from a copper substrate, tensile Young's modulus, and tensile strain-at-break were determined and SEM observations made as a function of the MAH concentration for each PP. One of the PPs plus 3 wt% MAH provides a high value of the adhesive strength along with the Young modulus and the strain-at-break sufficient for the use as a coating for copper wires and cables.     

Surface characterization of fluorinated polymers (PTFE,PVDF, PFA) for use in ultratrace analysis

Surface characterization of new unused PTFE, PFA and PVDF labware has been carried out by light microscopy, scanning electron microscopy, profilometry and atomic force microscopy. It has been found that in spite of higher micro-roughness, PFA exhibits the lowest nano-roughness and hence seems best suited as vessel material for relatively mild pressureless chemical operations for sample preparation of ultrapure substances, as container material for storage of ultrapure liquids, and for transport of such liquids, e.g., from the producer in the chemical to the end user in the microelectronics industry. This suitability refers only to the surface quality of the investigated materials. PTFE-surfaces, due to the sintering process of production, exhibit the most unfavourable surface quality of the investigated fluorinated polymers.     

Surface modification of titanium with thermally treated polydimethylsiloxane coating and the effect on resin to titanium adhesion

In this study, titanium surface modification by a thermal treatment using a polydimethylsiloxane (PDMS) coating was investigated. The surfaces of four titanium samples were surface treated by polishing, sandblasting, and coating with a PDMS with a thermal treatment at 800 and 1100 °C. The titanium surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy. The effect of the surface treatments on adhesion of resin to titanium was assessed by shear adhesion strength test. XPS analysis showed that there was a change of elemental composition of titanium surfaces after surface treatment. Binding energy shifts for Si2p and O1s were observed after sandblasting and thermally treated PDMS. Therefore, chemical states of Si and O were changed. Atomic force microscopy analysis revealed that the surface topography of the Ti samples was different, and surface roughness was increased after sandblasting and thermal treatment of PDMS coating. Shear adhesion strength test results showed that the adhesion between resin and titanium is affected by the treatment temperature of PDMS coating. The highest adhesion is obtained at 1100 °C (14.7 ± 1.57 MPa). Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular and nanoscale factors governing pressure‐sensitive adhesion strength of viscoelastic polymers

Pressure‐sensitive adhesives (PSAs) are finding increasing applications in various areas of industry and medicine. PSAs are a special class of viscoelastic polymers that form strong adhesive joints with substrates of varying chemical nature under application of light external bonding pressures (1–10 Pa) over short periods of time (1–5 s). To be a PSA, a polymer should possess both high fluidity under applied bonding pressure, to form good adhesive contact, and high cohesive strength and elasticity, which are necessary for resistance to debonding stresses and for dissipation of mechanical energy at the stage of adhesive bond failure under detaching force. For rational design of novel PSAs, molecular insight into mechanisms of their adhesive behavior is necessary. As shown in this review, strength of PSA adhesive joints is controlled by a combination of diffusion, viscoelastic, and relaxation mechanisms. At the molecular level, strong adhesion is the result of a narrow balance between two generally conflicting properties: high cohesive strength and large free volume. These conflicting properties are difficult to combine in a single polymer material. Individually, high cohesive interaction energy and large free volume are necessary but insufficient prerequisites for PSA strength. Evident correlations are observed between the adhesive bond strengths of different PSAs, and their relaxation behaviors are described by longer relaxation times. Innovative PSAs with tailored properties can be produced by physical mixing of nonadhesive long‐ and short‐chain linear parent polymers, with groups at the two ends of the short chains complementary to the functional groups in the recurring units of the long chains. Although chemical composition and molecular structure of such innovative adhesives are unrelated to those of conventional PSAs, their mechanical properties and adhesive behaviors obey the same general laws, such as the Dahlquist's criterion of tack. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Surface graft polymerization of glycidyl methacrylate onto polyethylene and the adhesion with epoxy resin

Surface graft polymerization of glycidyl methacrylate (GMA) was carried out onto a high- density polyethylene (PE) sheet pretreated with corona to introduce peroxides onto the PE surface. Graft polymerization of GMA was effected by UV irradiation of the coronatreated PE in the presence of monomer solution without the use of any photosensitizer. The graft layer was found by staining the PE cross section to localize in the surface region of PE. The physical change in the PE surface was characterized by scanning electron microscopy, while the chemical changes due to the GMA graft polymerization were assessed by the dynamic contact angle, FT-IR, and x-ray photoelectron spectroscopy (XPS) measurement. The peroxide formation by corona exposure was confirmed by the XPS measurement after derivatization with SO₂. The epoxy groups introduced onto the PE surface by the GMA graft polymerization were reactive with water (in the presence of HCI) and amines. The adhesion between the GMA-grafted PE and an epoxy resin was studied by means of a shear strength test method. The GMA-grafted PE exhibited strong interfacial adhesion with the epoxy resin, compared to the original and corona-treated PE. The adhesion strength of the GMA-grafted PE was nearly two times higher than that of the corona-treated PE. This strongly suggests that the enhanced adhesion between the surface-grafted PE and the epoxy resin is ascribed to covalent bonding of the epoxy groups on the GMA-grafted surface to the amines in the epoxy resin. © 1995 John Wiley & Sons, Inc.     

Surface chemistry studies in relation to adhesion

Summary The paper reviews recent surface chemistry studies, concerning aluminium adhesive joints. The work of adhesion corresponds to breaking stresses ten times those observed. This result may point to the effect of stress concentrations. Actually work of adhesion is still relevant to joint stress in so far as it effects spreading of the adhesive, and thereby a) contact area, b) contact angle at the free meniscus, c) radii of trapped air bubbles. The enthalpy of adhesion may be evaluated for cases where the work of adhesion is inaccessible (i. e. contact angle equal zero). It has been determined for a range of liquids and epoxypolymers with aluminium powder. When compared with results on the failure load of aluminium epoxy-polymer joints, it is inferred that the latter was not determined byinterfacial crack propagation in this instance, but more probably by cohesive failure. The results point to the importance of oxide film structure in determining heats of wetting.

---

Zusammenfassung Es wird ein Überblick über die Grenzflächenstudien gegeben, der Aluminiumklebverbindungen betrifft. Die Adhäsionsarbeit entspricht Bruchspannungen, zehnmal größer als beobachtet. Dieses mag auf dem Effekt von Spannungskonzentrationen beruhen. Die tatsächliche Adhäsionsarbeit bleibt noch insofern bedeutsam für Festigkeit von Klebung, als sie das Spreiten des Klebstoffes beeinflußt, a) die Kontaktfläche, b) den Kontaktwinkel am freien Meniskus, c) den Radius von eingeschlossenen Luftblasen. Die Adhäsionsenthalpie kann für Fälle, in denen die Adhäsionsarbeit unzulänglich ist, ausgewertet werden (z. B. für den Kontaktwinkel 0). Sie wurde für eine Reihe von Flüssigkeiten und Epoxyharzen und Aluminiumpulver bestimmt. Verglichen mit den Ergebnissen der Bruchlast von Aluminium-Epoxyharz-Klebstellen läßt sich schließen, daß letztere nicht durch Ausbreitung des Oberflächenbruches, sondern wahrscheinlicher durch Klebfehlstellen bestimmt wird. Die Ergebnisse weisen auf die Wichtigkeit der Oxidfilmstruktur beim Bestimmen von Benetzungswärmen hin.

     

Synthesis of fluorinated polymers via ROMP: a review

This review is concerned with the work conducted in the Durham group during the last twenty years. It is specifically concerned with ROMP of fluorinated monomers with classical and well-defined initiators, with the synthesis of stereoregular polymers, block and stereoblock copolymers.     

Microbial adhesion to zirconium alloys

We present data and analyses concerning the adhesion of clinically relevant Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa (bacteria) and Candida albicans (yeast) to Zircaloy-2 (Zry-2) and Zircadyne-705 (Zr705) surfaces. These zirconium-based materials are similar to those now being used in total hip and knee replacements. Here we study clinical strains of microbes under shaken and stationary exposure conditions, and their ability to adhere to Zr surfaces having different oxide thicknesses. We use X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), viable counts, endotoxin assays, and statistical analysis methods, and demonstrate a predictive model for microbial adhesion based on XPS data.     

Surface properties of fluorinated single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) were fluorinated at several different temperatures. The change of atomic and electronic structures of fluorinated SWCNTs was investigated using X-ray photoelectron spectroscopy (XPS), electrical resistivity measurements and transmission electron microscopy (TEM). The amount of doped fluorine increases with increasing doping temperature, and the fluorine atoms are covalently attached to the side-wall of the SWCNTs. From Raman spectra and HRTEM study, the strong fluorination on the SWCNTs leads to the breaking of carbon–carbon bonds and the disintegration of tube structure. Several intermediate phases of fluorinated SWCNTs are observed during e-beam irradiation in HRTEM.