Examination of polymer surfaces

We provided an overview of combinatorial and high-throughput methods research at NIST, with a focus on tools and application examples that are useful for the examination of polymer surfaces, interfaces and thin films. An examination of this body... 

The book covers not only instrumentation for the determination of metals, non metals, functional groups, polymer structural analysis and end-groups in the main types of polymers now in use commercially, but also the analysis of minor non-polymeric components of the polymer formulation, whether they be deliberately added, such as processing additives, or whether they occur adventitiously, such as residual volatiles and monomers and water. Fingerprinting techniques for the rapid identification of polymers and methods for the examination of polymer surfaces and polymer defects are also discussed. 

This technique has been applied to the examination of polymer surfaces [9]. 

The use of DIC in the study of polymers is particularly well suited to situations such as etched surfaces (see sections 10.3.2.2 and 10.4.2.3), which are macroscopically flat but which nevertheless contain fine topographic details [45]. However, the direct examination of polymer surfaces in reflection is not always entirely straightforward because of the low reflectivity exhibited by many systems. It is therefore often desirable to evaporate or sputter a reflective metallic coating on to the specimen surface prior to examination. While this improves the reflectivity of the sample it also has another less obvious benefit. In low-absorbance systems, the illumination may be reflected back into the objective lens not only from the surface of the specimen, but also from other boundaries within the sample. Particularly at low magnifications, where the depth of field may be considerable in comparison with the size of the surface features, such subsurface effects may give a false impression of the sample topography. 

FTIR-AFM examination of polymer surfaces, morphology, adhesion studies, photooxidative stability, particle size, and helix structure studies. 

It was observed elsewhere that plasma treatment of polymer macromolecules results in their cleavage, ablation, alterations of chemical structure and thus affects surface properties e.g. solubility [75]. The effects of the treatment in Ar plasma on the surface properties of PE were examined in [72]. The parameters of the plasma discharge (240 s, 8.3 W power) were chosen, on the basis of our previous experiments [70-74,78], to guarantee the most pronounced changes of polymer surface. Mean thickness of the ablated PE layer was calculated from the weight difference measured by gravimetry. By Ar plasma (8.3 W, 240 s) 30 8 nm thick surface layer is ablated and thickness of the surface layer removed from plasma-modified PE by 24 hour water etching is 21 5 nm [78]. 

Raman spectroscopy can offer vibrational information that is complementary to that obtained by IR. Furthermore, since the Raman spectrum reveals the backbone structure of a molecular entity [55], it is particularly useful in the examination of polymer film-coated electrodes. There are also some distinct advantages over in situ IR. For example, both the mid and far infrared spectral regions can be accessed with the same instrumental setup (in IR spectroscopy, these two regions typically require separate optics) [55]. Second, solvents such as water and acetonitrile are weak Raman scatterers thus the solvent medium does not optically obscure the electrode surface as it does in an in situ IR experiment. 

Modifications of polymer surfaces by exposure to electrical plasmas and discharges have also been subjected to XPS examination in several recent articles (4, , 7). An example is the plasma oxidation of polyethylene, polypropylene and polystyrene in a radiofrequency inductively coupled system ( ). Figure 14 shows the Cls and 01s spectra of a polyethylene film after... 

Several authors have reported that protein adsorption is a maximum on hydrophobic substrates whereas others claim that it is more pronounced on hydrophilic surfaces (15=12). In an attempt to clarify the situation and to elucidate the fundamental mechanisms involved in bioadhesion we have examined the adhesion of various biological cells to a number of polymer surfaces (28-33). The... 

All the methods described so far suffer from the disadvantage that they allow only the study of very thin films of polymer, by direct TEM, or of polymer surfaces, by replication. Thin enough films are difficult to make and neither they nor surfaces produced by casting or by fracture are necessarily typical of bulk material. It is therefore desirable to have a technique that can be used for any surface, including one cut from the interior of a larger sample. A technique that allows any type of surface to be prepared in a way suitable for the examination of the underlying structure is the use... 

Potts used the method in his screening of 31 commercially available polymers for biodegradability. Other studies, where the growth of either mixed or pure cultures of micro-organisms, is taken to be indicative for biodegradation, have been reported. The validity of this type of test, and the use of visual assessment alone has been questioned by Seal and Pantke for all plastics. They recommended that mechanical properties should be assessed to support visual observations. Microscopic examination of the surface can also give additional information. 

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