Characterization of Surface Pretreatments on Al/Li Alloy and Related Mechanical Properties of Polysulfone Adhesive Bonds

An investigation of polysulfone-Al/Li alloy interaction involved single lap shear joints and wedge samples following an FPL etch, sulfuric acid anodization (SAA) and phosphoric acid anodization (PAA). The study of the Al/Li surfaces involved the determination of the elemental composition and morphological features of the pretreated adherend before bonding and following fracture. When polysulfone was either thermally pressed or primed onto the microporous surface, the polysulfone indeed penetrated into the porous oxide and thereby provided a mechanical means of adhesion. The wedge test results for the adherend pretreated by PAA and SAA were superior to those for the FPL etched adherend. The failure path for the FPL etched samples was at the adhesive/oxide interface whereas the failure path for the PAA samples was within the adhesive but with occasional divergence of the crack into the oxide. The porous oxides on Al/Li alloy formed after PAA and SAA treatment were shown to undergo dramatic changes in morphology on short term (< 95 hrs) exposure to 71°C and 100% R.H. environment. The mechanism of failure was due to moisture which caused hydration and subsequent weakening of the surface oxide layer and the bonded joint. Lithium was not surface concentrated in the PAA treated Al/Li alloy as shown by AES depth profiling and therefore the effect of Li on the durability of the bonded alloy is considered minimal.     

Adhesion Promotion by Silanes: A Study of their Interfacial Chemistry in a Model Polystyrene Coating by XPS and SIMS

Adhesion of a polystyrene coating to solvent cleaned steel is increased two-fold by addition of 0.5% wt/wt of aminosilane (A1120). A study has been carried out on the coating-substrate interfacial chemistry to gain an understanding of the mechanism of adhesion promotion. It is shown that in peel experiments the coating fails adhesively between the polystyrene and an adsorbed layer of aminosilane on the steel surface. The improvement in adhesion results from displacement by the silane of the 1.4 nm thick layer of residual carbonaceous contamination on the steel surface. It is proposed that this leads to a stronger substrate-coating interaction either through improved intermolecular contact between the segregated silane and the polymer or through secondary bonding between the amine groups of the silane and the polarisable aromatic rings of the polystyrene.     

Relaxation Properties and Chemical Nature of Polymer Surface Layers as Related to the Strength of Adhesive Joints with Metals

A new approach based on the theory of elasticity is proposed to study relaxation properties of adhesive transition layers. It involves experimental evaluation of the rate dependence of the fracture energy of the bulk polymer and its adhesive joint.

The investigation of the interaction of a polymer surface layer with electroplated copper by XPS using the effect of differential charging (the latter produced by potential shift of the sample by 10V), makes it possible to identify the functional groups of adhesive brought into contact with substrate surface. For ABS copolymers a bond of -O … Cu type was formed.

The mechanism of adhesive contact formation and factors affecting the strength of adhesive joints could be understood better by determining the properties of surface and transition layers.     

Adhesion Studies of Fluoropolymers

A comparative study of the treatment of polytetrafluoroethylene (PTFE) and poly(vinyl fluoride) (PVF) with “Tetra-Etch” has been carried out. The treatment of PTFE resulted in extensive changes in surface chemistry and topography, whereas with PVF there was no significant change in topography and the chemical changes were much less marked. However, treatment of both polymers resulted in large increases in bond strength.

Multiple bonding experiments in which samples are repeatedly fractured and re-bonded were carried out with untreated PTFE and PVF. These resulted in moderate increases in bond strength with PTFE and large increases with PVF. The results indicate that weak boundary layer (WBL) removal is a key element in adhesion improvement by “Tetra-Etch” on PVF. With PTFE, WBL removal also improves adhesion, but the chemical and/or topographical changes introduced by the “Tetra-Etch” are required for optimum performance.     

Interphase Formation and the Characterisation of Polymer/Ceramic Adhesion

The adhesion of photocured resins to ceramic substrates has been investigated using a variety of surface analytical techniques. Work has been aimed at establishing the physical and chemical interactions between resin and substrate in the interphase region and the effect of environmental exposure on these Analysis was aided by use of specially-designed, in-situ fracture facilities attached by an X-ray photoelectron spectrometer. Specific attention was focused on identification of localised regions of varying chemical composition in adhesive and adherend by imaging spectroscopies (imaging XPS and ToF SIMS imaging) and the study of the significance of such heterogeneities on adhesion and subsequent failure mechanisms.     

Surface Characterization of Chlorinated Synthetic Vulcanized Styrene-Butadiene Rubber Using Contact Angle Measurements,Infra-Red Spectroscopy and XPS

The surface of a sulfur-vulcanized synthetic styrene-butadiene rubber (SBR) was treated with ethyl acetate solutions containing different amounts of trichloroisocyanuric acid (TCI). The chlorinated SBR surfaces were characterized using contact angle measurements (water, ethane diol, n-hexadecane), infra-red (IR) spectroscopy and XPS. Chlorination produced an increase of surface free energy which was mainly due to the enhancement of the acid-base component of the surface free energy, which remained almost unchanged when the amount of TCI was increased. Depending on the amount of chlorination agent, several chemical species were present on the SBR surface: i) For low amounts of TCI (up to 2 wt%), mainly chlorinated hydrocarbon and C – O species were present on the surface; ii) For medium amounts of TCI (between 2 and 5 wt%), an excess of unreacted TCI remained on the surface and a relatively small amount of isocyanuric acid was deposited; iii) For high amounts of TCI (larger than 5 wt%), a weak boundary layer (mainly composed of isocyanuric acid) was formed on the surface and thus the effects due to chlorination were decreased. There was good agreement between the experimental results obtained with contact angle measurements and XPS because both provided information on a surface region close to 100 Å, whereas IR spectroscopy results showed deeper penetration of the chlorinating agent into the SBR surface. The estimated thickness of the chlorinated layer was near 5000 Å as estimated from XPS measurements of SBR surfaces modified by argon ion bombardment.     

Development of antimicrobial stainless steel via surface modification with N‐halamines: Characterization of surface chemistry and N‐halamine chlorination

N‐halamine modification of materials enables the development of antimicrobial materials whose activity can be regenerated after exposure to halogenated sanitizers. Surface and bulk modification of polymers by N‐halamines has shown great success, however, modification of inorganic substrates (e.g., stainless steel) remains an area of research need. Herein, we report the covalent surface modification of stainless steel to possess rechargeably antimicrobial N‐halamine moieties. Multilayers of branched polyethyleneimine and poly(acrylic acid) were immobilized onto the surface of stainless steel and the number of N‐halamines available to complex chlorine was quantified. Samples were characterized through contact angle, Fourier transform infrared spectroscopy, ellipsometry, dye assay for amine quantification, and X‐ray photoelectron spectroscopy. Increasing the number of multilayers from one to six increased the number of N‐halamines available to complex chlorine from 0.30 ± 0.5 to 36.81 ± 5.0 nmol cm^?2. XPS and FTIR confirmed successful covalent layer‐by‐layer deposition of the N‐halamine multilayers. The reported layer‐by‐layer deposition technique resulted in a greater than seven‐fold increase of available N‐halamine compared to prior reports of N‐halamine surface modifications. The N‐halamine modified steel demonstrated antimicrobial activity (99.7% reduction) against the pathogen Listeria monocytogenes. Such surface modified stainless steel with increased N‐halamine functionality, and therefore potential for rechargeable antimicrobial activity, supports efforts to reduce cross‐contamination by pathogenic organisms in the food and biomedical industries. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Surface oxidation of single-walled carbon nanotube paper with oxygen atoms

Single-walled carbon nanotube paper was surface oxidized with gaseous oxygen atoms produced by low-pressure: (1) vacuum UV (λ?=?104.8 and 106.7?nm) photo-oxidation and (2) downstream microwave plasma discharge of an Ar–O₂ mixture. X-ray photoelectron spectroscopy was used to detect the carbon- and oxygen-containing functional groups in the top 2–5?nm of the sample’s surface. Both methods produced a saturation level of ca. 12 at.% oxygen with the predominant formation of the epoxide/ether groups.     

Adhesion Performance and Microscope Morphology of UV-Curable Semi-interpenetrated Dicing Acrylic PSAs in Si-Wafer Manufacture Process for MCP

UV-curable acrylic pressure-sensitive adhesives (acrylic PSAs) have many applications in industry. As the Si-wafers become thinner, the acrylic PSAs for MCP need to show proper adhesion and leave little residue on the Si-wafer after UV irradiation when released from the dicing tapes. Strong adhesion is required in the dicing process to hold the Si-wafer before UV irradiation. On the other hand, weak adhesion strength is required after UV irradiation to prevent damage to the Si-wafers during the pick-up process. This study employed semi-interpenetrating polymer network-structured dicing of acrylic PSAs in the Si-wafer manufacture process. The binder PSAs contained 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AA). The adhesion performance of the peel strength on a Si-wafer was examined as a function of the UV dose. The results showed that the abovementioned two requirements were achieved using semi-IPN dicing acrylic PSAs using a hexafunctional acrylate monomer and a UV-curing system. FE-SEM and XPS revealed little residue on the wafer after removing the tape. This paper suggests the optimal conditions for the curing agent, the additional hexafunctional monomer, photoinitiator and the coating thickness.