Hydrophobic polymers, surface contamination

For hydrophobic polymers, which are non polar and are characterized by a low surface energy, the surface contamination does not seem to be a problem. The situation is less clear in the case of organic surfaces that expose polar groups such as OH- or COOH-terminated self-assembled monolayers. It is indeed difficult to decide whether unexpected results should be attributed to preparation failure or to contamination subsequent to preparation (unpublished results). 

Alternate explanations for the loss of hydrophilicity upon aging include the blooming of hydrophobic impurities in the polymer to the surface (30), or the deposition of ubiquitous airborne contaminants onto the surface. However, since the (TD)2DPM surfaces can remain relatively hydrophilic for up to 1 year, these are probably not significant factors in the loss of hydrophilicity. It should be noted that oxidized polydiene films (exposed to air 1 year) can display contact angles as low as 65°. 

Most silicone polymers act as very good insulators. Polarity of the slloxane backbone apparently is shielded by methyl groups. In addition, the hydrophobic nature of the surface helps to repel water (and dissolved ionic contaminates) which assures the retention of insulation properties under difficult conditions. One application where these properties have found recent importance has been for insulator sheds. Even after repeated exposure to salt fog and high voltage stress, the materials retain their resistance to conductive and arc failure (33). 

Metal-polymer nanocomposites can be obtained by two different approaches, namely, in situ and ex situ techniques. In the in situ methods, metal particles are generated inside a polymer matrix by decomposition (e.g., thermolysis, photolysis, radiolysis, etc.) or chemical reduction of a metallic precursor dissolved into the polymer. In the ex situ approach, nanoparticles are first produced by soft-chemistry routes and then dispersed into polymeric matrices. Usually, the preparative scheme allows us to obtain metal nanoparticles whose surface has been passivated by a monolayer of -alkanethiol molecules (i.e., Crfiin+i-SH). Surface passivation has a fundamental role since it avoids aggregation and surface oxidation/contamination phenomena. In addition, passivated metal particles are hydrophobic and therefore can be easily mixed with polymers. The ex-situ techniques for the synthesis of metal/polymer nanocomposites are frequently preferred to the in situ methods because of the high optical quality that can be achieved in the final product. 

C7H7O3 ), and 193 (unknown). These peaks were indicative of HEMA with little resemblance to MA. If MA was present, there would be a predominant peak at 158 amu. In addition, the negative ion spectra are typically considered more sensitive to the methacrylate polymer structure than positive ion spectra. Thus, there would be no spectroscopic evidence to suggest that MA was present on the surface of the dry cast-molded lenses analyzed here. It may be that the MA rearranged upon drying of this polymer. The spectra obtained in the ToF SIMS for the lathed Eta-filcon-A revealed a surface dominated by the presence of contamination from processing aids. The use of isopropyl alcohol (IPA) extraction removed the residual silicone and the hydrophobic pitch or wax. 

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