New Pretreatment for Elastomers to Enhance Adhesion

The effects of various chemical pretreatments on the surface chemistry and adhesion performance of an additive-free styrene-butadiene block copolymer and an additive-free ethylene-propylene elastomer have been studied. Most of the powerful oxidising agents that are effective with hydrocarbon plastics were ineffective in enhancing the adhesion to elastomers despite causing major changes to their surface chemistries. The poor adhesion was attributed to the existence of weak boundary layers. Chlorinated agents were also examined and a new pretreatment for elastomers containing carbon-carbon double bonds has been identified. It was found that a mildly acidified dilute aqueous suspension of Chloramine-T was very effective at enhancing the adhesion performance of styrene butadiene copolymers.     

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.     

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.     

Experimental determination of solidified lithium disilicate crystal bandgap energy using EELS and XPS

Lithium disilicate (LS2) has been a crucial parent composition for glass-ceramics since the 1950s because of its excellent chemical and physical durability. In addition, a wide range of electrical properties can be obtained by changing the composition and crystallinity. Bandgap energy is one of the critical electrical properties for designing new lithium silicate-based materials. In this study, the bandgap energy of a synthesized LS2 crystal is evaluated using electron energy-loss spectroscopy and X-ray photoelectron spectroscopy. These two techniques unambiguously establish that the bandgap energy of LS2 is 7.7-7.8 eV, which is in the vacuum ultraviolet region. This confirms the insulating nature of the LS2 crystal.     

Film Structure and Adhesion

Paint films although attached to a substrate on one side only may be subjected to stresses, comparable to those in structural adhesives. These stresses result from shrinkage during film formation and subsequent ageing, mechanical strains, relative thermal movements of film and substrate and from osmotic pressure due to soluble material under or within the film. The adhesive strength required to prevent detachment varies from very little for weak, highly porous coatings to 10,000 lb/in² for tough coatings of high elastic modulus. Generally, adhesive strength both to the substrate and between coats in a paint system must exceed cohesive strength, under the conditions when failure is likely to develop. Dispersion and other forces, such as hydrogen bridging, between coatings and clean metal substrates should suffice to ensure adhesion but most practical surfaces carry contaminants, which interfere with wetting and intimacy of contact. Solvents and other low molecular weight components may also provide a weak interfacial layer, at least for a period after application. Modification of polymer structure to improve contaminant displacement and to increase polymer/substrate interaction forces, for example by the introduction of polar substituent or end groups will be discussed and potentialities of adhesion-promoting surface treatments reviewed.     

Surface segregation in blends containing poly(dimethylsiloxane)-polystyrene block copolymers

The surface composition of polystyrene blends containing poly(dimethylsiloxane)-polystyrene block copolymers have been analyzed using X-ray photoelectron spectroscopy (XPS), contact angle measurements, and time-of-flight secondary ion mass spectrometry (TOFSIMS). The three techniques showed the surface of the blend samples to be identical to pure poly(dimethylsiloxane) homopolymer, despite the fact that the systems each contained only a 2% bulk concentration of siloxane. The high surface sensitivity of TOFSIMS—which probes the samples to depths of a few angstroms—indicates an enrichment of-Si(CH₃)₃ groups at the surface. These are the terminal groups of the PDMS part of the block. Their enrichment at the surface of the samples is presumably due to their low surface energy, in addition to the tendency for end groups to be at the surface due to free volume considerations.Presented at the XXVIth Silicon Symposium, Indiana University-Purdue University at Indianapolis, March 26–27, 1993.     

A Study on Hydrophobic Surface Coatings with Abrasion Resistance Property

The aim of this study is to synthesize a hydrophobic surface coating with abrasion-resistant inorganic-organic hybrid materials. First, the copolymer of poly (MMA-co-MPTS)-colloid silica was synthesized by using the free radical polymerization of the methyl methacrylate (MMA) with γ-methacrylate propyltriethoxysilane (γ-MPTS). Next, the copolymer was hydrolyzed with tetraethoxylsilane (TEOS), fluoroalkylsilane (FAS), and colloid silica in the weak acid condition by a sol-gel process to obtain the surface coatings of hybrid material of poly (MMA-co-MPTS)-colloid silica. Finally, the effects of the colloid silica content on the optical properties, abrasion resistance, and morphology of the hybrid surface coatings were discussed in this study.     

Evaluation of the Interaction and Adsorption of γ-Glycidoxy propyl trimethoxy silane with Grit-Blasted Aluminium: A ToF-SIMS and XPS Study

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) have been employed to study the adsorption and interaction of γ-glycidoxy propyl trimethoxy silane (GPS) with grit-blasted aluminium.

GPS displaces adventitious hydrocarbon either by covalent bond formation between GPS and aluminium, or adsorption, when GPS is deposited on the aluminium. ToF-SIMS fragments present at a nominal mass m/z = 71 were peak-fitted to seven peaks by using CasaXPS Software. AlOSi⁺ and Si⁺ were used to establish a relationship between covalent bond formation and the adsorption process. It is found that the adsorption isotherms of Si⁺ relating to the adsorption of GPS were of the Langmuir type. The interfacial bonding between GPS and aluminium is mainly covalent at low solution concentrations. At higher concentrations (greater than 4.5 × 10^?4 M) all the sites for the covalent bond formation appear to be occupied while these for the acid-base interaction are still available and then become fully occupied at solution concentrations of 4.5 × 10^?2 M and above.     

强碱-阳极氧化法处理Ti片制备TiO_2薄膜的研究

本文利用强碱-阳极氧化法对钛片进行改性,制备TiO2薄膜;用扫描电镜（SEM）、X射线光电子能谱（XPS）考察了不同电解液浓度下氧化电压对TiO2氧化膜形貌及组成的影响。结果发现,在本实验条件下,该法制得的氧化膜是由三种钛氧化物组成的,主要成分是TiO2,此外还有低价钛氧化物Ti2O3及TiO;氧化电压的不同会对薄膜形貌产生重要的影响,当氧化电压较高时,氧化膜的厚度比较厚且致密;钛表面生成氧化膜大致过程可概括为：Ti→TiO→Ti2O3→TiO2,其中TiO转为为TiO2的几率依靠电势的大小及氧化时间的长短。     

Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.     

Adhesion Science and Surface Analysis. Typical Examples

A number of surface modification methods using mechanical, chemical, electrochemical or physical processes have commonly been employed to treat adherend surfaces and improve adhesion in various bi- or multi-layered systems which play a key role in many advanced technologies. Results reported in this review paper deal more particularly with components of polymer-metal systems and provide typical examples of surface analysis obtained by x-ray photoelectron spectrometry (XPS), ion scattering spectrometry (ISS), low-energy electron induced x-ray spectrometry (LEEIXS), optically stimulated electron emission (OSEE) and Fourier transform infra-red spectrometry (FTIR). These examples concern, on the one hand, metallic adherends (aluminum, stainless steel, zinc-coated steel, gold) the surfaces of which were modified by cleaning, etching, oxidation, conversion or chemical grafting and, on the other hand, bonded joints (polyester-steel and epoxy-aluminum systems) which were delaminated using a peel test and a three-point flexure test, respectively.     

New developments in polymer surface analysis

Surface and interface characterization of polymeric materials has not enjoyed the multi-technique approach which typifies other types of materials. X-ray photoelectron spectroscopy (XPS) has dominated, despite several major disadvantages. New approaches are discussed which either improve XPS (particularly derivatization techniques) or utilize ‘static’ secondary ion mass spectrometry (SIMS) to overcome these limitations, with examples of their application in materials problem solving.     

Structural and Optical Studies on Sol-gel Composites of Nickel-Doped Nanocrystalline Zinc Oxide/Polyvinylidene Fluoride

Nickel-doped nanocrystalline ZnO with three different Ni concentrations was incorporated in polyvinylidene fluoride thin film for obtaining free-standing flexible film by sol-gel technique. The effect of Ni–ZnO loading on the optical and microstructural properties of the Ni–ZnO/polyvinylidene fluoride composite films was studied. X-ray photoelectron spectroscopy and Raman studies were performed to characterize the bonding environment. Fluorine-terminated surface showed a strong F1?s peak located at ～695?eV arising out of C–F bonds. Existence of β phase of polyvinylidene fluoride along with the presence of ZnO nanocrystals were indicated by Raman studies. Secondary ion mass spectrometry studies indicated the distribution of Ni–ZnO particles in the polyvinylidene fluoride matrix.     

The oxidation of carbon monoxide on Rh(100) under steady state conditions: An FT-IR study

The steady-state oxidation of CO on clean Rh(100) at low pressures has been investigated using in-situ infrared spectroscopy and mass spectrometry. The results show that at a fixed CO pressure, the temperature at which the CO₂ formation rate maximizes decreases as a function of increasing O₂ pressure. Vibrational data indicate that this maximum rate coincides with a CO coverage of less than 0.01 monolayers.     

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.     

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.     

Adhesion Between Plasma-Treated Polypropylene Films and Thin Aluminum Films

Polypropylene (PP) film was treated with radio-frequency-induced oxygen plasma, followed by the vacuum deposition of aluminum (Al) thin film, and the peel strength of the Al deposited PP film (Al/PP) was examined. The peel strength of plasma-treated PP film varied widely in the range of 6.7 to 157 N/m depending upon the plasma treatment conditions, whereas that of the untreated PP was 5.2 N/m. The peel strength was minimized at oxygen pressure near 13.3 Pa (0.1 Torr), and decreased with increasing discharge power. The peel strength rapidly increased at the initial stage of plasma treatment (∼ several seconds), decreased at the second stage, and slightly increased again at the third stage. A good agreement was found between the peel strength of Al/PP and the amounts of oxygen introduced onto the PP surface at the initial stage. A short-time treatment was very effective to improve the adhesion of Al/PP. At the end of the second stage, a large amount of carbon was detected by XPS on the Al layer of the peeled interface of Al/PP, which gave a minimum peel strength. Cohesive failure of PP film might have occurred. SEM photograph showed that PP surface was etched by oxygen plasma at the thrid stage. These peel behaviors of Al/PP were explained by the chemical and physical changes of the PP surface caused by oxygen plasma treatment: (1) introduction of O-functional groups onto the PP surface at the initial stage, (2) formation of weak booundary layers resulting from the partial scission of PP molecules at the second stage, and (3) plasma etching of the PP surface at the third stage.     

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.