James Tonge

Behavior of plasma-treated elastomeric polydimethylsiloxane coatings in aqueous environment

Plasma treatment is a useful way of enhancing the wettability of polydimethylsiloxane (PDMS). The subsequent recovery of hydrophobicity in air once treatment is discontinued is well known, but less has been reported about the effect of the storage environment. Water storage is the most relevant, with some reports that this stops the hydrophobic recovery of plasma-treated Medical Grade PDMS elastomer. This is not our experience with a commercial industrial PDMS sealant that had been treated by a helium radio-frequency plasma and stored in pure water and in artificial sea water. Substantial hydrophobic recovery occurs on storage in these environments. The commercial sealant is likely to have more low molecular weight diffusible species and more pre-existing silanol groups than the Medical Grade material. Both of these factors could affect the recovery mechanism by diffusion of untreated polymer chains to the surface or reorientation of polar and non-polar groups in the surface region.

Reliability of Silicone Encapsulants in high Pollution Environments.

Photovoltaic cells and their encapsulants are subjected to harsh environments with extremes in solar radiation, thermal/humidity cycling, mechanical stress, electrical bias and increasing levels of pollution. Volcanic action and the escalating use of fossil fuels have increased the threat of atmospheric sulfurous gaseous on silver and other metal contact materials. Twenty years ago Cuddihy et. al., concluded that elastomeric silicone encapsulants were the only technology to meet all the physical, chemical, spectral, and mechanical demands of photovoltaic modules. In the decades since the decision to excluded silicone in this application for cost reasons, the thermal and photo-degradation of Ethylene Vinyl Acetates, EVAs, continues to be well documented. It can be concluded from recent work on water vapor transmission rates that sufficient water can penetrate todays EVA cells to fuel the corrosion processes mitigating hard fought efficiency gains. Today silicones are in wide-spread use as frame or junction-box sealants in the PV industry to protect against water/moisture ingress into EVA or electrical connections, as well as to protect bypass diodes and soldering points in junction box potting applications. Future forecast are cure speeds will be ramped up, and PV module prices will be progressively driven down, is it time to reconsider this proven silicone technology? Dow Corning Corporation has expanded their studies to include the growing list of sulfur-based industrial pollutants. The results of continuous corrosion rate monitoring of silicone encapsulated silver circuits on glass substrates reconfirms the benefits of silicone encapsulants in this application

Silicon-acrylic sol-gel modified automotive clear topcoats for etch and scratch resistance

SummariesAutomotive clear topcoats must provide superior resistance against mechanical and chemical damage to guarantee long-term aesthetic appearance. Vehicle manufacturers have extended coating warraties while the performance demands have increased. Reported here are etch and scratch resistant clear topcoat formulations of silicon-acrylic sol-gels with acrylic-melamine and acrylic-isocyanate systems. These one and two-part thermally-cured formulations were applied to typical automotive melamine basecoats. Industry standard performance testing and micro and nanoscratch evaluations are compared, and contrasted with non sol-gel-containing formulations.RésuméLes finitions claires pour automobiles doivent assurer de meilleure résistance à des dégâts et mécaniques et chimiques afin d’assurer à long terme l’aspectes ésthétiques. Les fabricants de véhicules ont prolongé des garanties concernant la peinture, tandis que les exigences à l’égard du rendement ont augmentées. Ici on donne un compte rendu de la résistance au mordançage et à la rayure des finitions à base des sol-gel modifiées résines de silicon-acrylique avec des systèmes acrylique-mélamines et acrylique-isocyanates. Les revêtements mono ou à deux composants thermodurscissables ont été appliqués aux usuelles peintures de fond de mélamine pour automobiles. Des méthodes d’essai normalisées en l’industrie et également les évaluations de la rayure et micro et nano sont comparées et contrastées auprès des finitions exemptes des constituants sol-gel.ZusammenfassungKlarautodecklacke müssen bessere Fähigkeit gengen mechanische und chemishe Shaden, um langfristig ästhetisches Aussehen zu garantieren, liefern. Fahrzeughersteller haben Lackgarantien verlängert, indem Leistungsbedürfnisse haben zugenommen. Hier wurden ätz-und kratzfestige Klarautodecklacke basiert auf sol-gelmodifizierte Silicium-Acrylmelamin und Acryl-Isocryanatsysteme berechtet. Diese thermohartenden Ein- und Zweikomponentenlacke wurden auf typische Melamin-Autobasislack angewandt. Die Normprüfungsmethoden für die Autoindustrie und Mikro-und Nanokratzauswertungen wurden mit den sol-gelfreien Beschichtungen verglichen und kontrastiert.