Modified polymer surface analysis

The application of modern surface analysis techniques, such as XPS, to the analysis of modified polymer surfaces, has demonstrated that in most of the above processes the polymer is oxidized. Many functional groups such as hydroxyl, carbonyl, ether, carboxyl, ester, peroxide, epoxide, etc., have been detected by direct XPS analysis or after derivatization of functional groups. The interaction between evaporated metal films and several of such functional groups has been clearly demonstrated (3). 

A surface analysis technique that has the potential to detect structural chemical changes in polymer surfaces, including low-molecular weight material formation, is static SIMS. Its capabilities for characterizing polymers by virtue of their fingerprint spectrum nave been amply demonstrated in recent years (5 6). The technique is more surface sensitive than XPS and can detect structural differences, even in hydrocarbons (7). It is, therefore, highly complementary to XPS. Nevertheless, only very few applications to the study of modified polymer surfaces have been published. Among these are reports on SIMS analysis of flame-treated polypropylene and plasma-fluorinated polyolefin surfaces (8 9). 

Explicitly developed are models of several theoretical multiphase distributions, with corresponding depth-profile results on thin-film plasma polymers, phase-separated block copolymers, and chemical reactions on fiber surfaces. Ion impact is treated from three points of view as an analytical fingerprint tool for polymer surface analysis via secondary ion mass spectroscopy, by forming unique thin films by introducing monomers into the plasma, and as a technique to modify polymer surface chemistry. 

In a pilot study, it was discovered that an ultraviolet zone (UVO) based method, which has been developed for surface treating wool fibers, could be used to oxidatively modify polymer surfaces. Electron spectroscopy for chemical analysis (ESCA) and contact angle results indicated that the treatment was effective on PE and a polyetheretherketone (PEEK). It produced changes in surface oxygen chemistry and free energy, which increased polarity and improved wettability of the surface. Composite lap shear tests showed that the treatment gave a marked improvement in adhesion and that an optimum joint strength is achieved at low treatment times (<1 min). 

Infrared spectroscopy, including Fourier-transform infrared (FTIR) spectroscopy, is one of the oldest techniques used for surface analysis. ATR has been used for many years to probe the surface composition of polymers that have been surface-modified by an etching process or by deposition of a film. RAIR has been widely used to characterize thin films on the surfaces of specular reflecting substrates. FTIR has numerous characteristics that make it an appropriate technique for... 

Adhesion of non-polar polymers is sometimes improved by oxidation, so essentially what is normally thought of as degradation may be used to introduce an enhancing surface property. Nevertheless, in both cases the oxidation process modifies the polymer surfaces, and the analysis tools can be rather similar, see, e.g., Ref. [101]. 

To characterize the properties of molecules and polymer films attached to an electrode surface, a wide variety of methods have been used to measure the electroactivity, chemical reactivity, and surface structure of the electrode-immobilized materials [9]. These methods have been primarily electrochemical and spectral as indicated in Table I. Suffice it to say that a multidisciplinary approach is needed to adequately characterize chemically modified electrodes combining electrochemical methods with surface analysis techniques and a variety of other chemical and physical approaches. 

The relative fragility and preparative difficulty associated with monolayer-modified electrode surfaces hampered significant analytical progress for some time, and it was not until polymer-film electrodes were developed that the utility of modified electrodes in analysis could be demonstrated. 

Polymer-based multicomponent systems are abundant in many applications. The properties and performance of particulate-filled systems, such as elastomers and impact modified polymers, and also polymer blends, block copolymers, and fiber reinforced systems, depend to a large extent on the distribution of the components. Hence the local analysis of these distributions down to sub-100 nm length scales (dictated, e.g., by the size of primary filler particles) is of considerable significance. Materials contrast in several AFM approaches offers the possibility to address these issues directly at the surface of specimens or on bulk samples that have been prepared correspondingly. 

It was demonstrated with surface analysis techniques that the polymer surface is modified selectively with different laser irradiation wavelengths. The two laser energy regimes, above and below the threshold for laser ablation, reveal pronounced differences. For both irradiation wavelengths (248 and 308 nm) the polymer surface modification is solely chemical after treatment with fluences below the threshold. Each irradiation wavelength leads to a surface oxidation, as shown with the contact angle and XPS measurements. The oxidation is a result of the radical pathway of photodecomposition of the triazene chromophore. 

The amount of bone nodule formation was quantified from the surfaces of unmodified and modified polymers at 28 and 35 days in culture under osteogenic conditions, for each of the three different pore-sized polymers. Histomorphometric analysis shows that the surfaces of modified polymers had significantly increased areas of Von Kossa staining (Figure 7.14) compared to unmodified polymers. Increased amounts of nodule formation can be observed for each of the different pore sizes between days 28 and 35 but this is only significant for 100-yum pore size. There was no evidence that nodule area was significantly influenced by the three pore sizes evaluated in this study. 

Both XPS and TOF-SIMS are nowadays standard analytical tools for the determination of biomaterials surface chemistry. Examples of the use of XPS or TOF-SIMS for the analysis of biomimetic polymers include the investigation of different protein " ° and phosphate group modified polymeric surfaces. 

FTIR spectroscopy was used for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) was used to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels. Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180 C, as evidenced by the frequency shift of the absorption band characteristic for nitrile groups. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 micrometers in diameter, indicate the presence of an ultrathin layer of modified polymer still covering the substrate. 28 refs. 

The adhesion power of metal electrode to perfluorosulphonic polymer is used to modify the surface of a single electrode for the analysis of electrochemical reactions of special interest. Nafion -coated electrodes have been developed by Rubinstein Bard" . Various electron-conducting materials (glassy carbon, gold, platinum) are used as support for the Teflon layer. With these coated electrodes, the mechanisms of mass and charge transfer in the perfluorosulphonic material have been investigated and also the catalytic and photochemical properties of polymer doped with various chemical species . ... 

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