Filled polymethylsiloxane (PDMS) composites are used for a number of important commercial and technological applications ranging from electronics to medicines and cosmetics. Even though PDMS itself is hydrophobic and lacks binding sites, the silica fillers used for mechanical strength in modified PDMS provide binding sites for moisture. Moisture outgassing from these filled PDMS materials may be responsible for the corrosion of other components in vacuum packages. Thus, it is important to understand the mechanism of interactions of moisture with polysiloxane materials as well as the subsequent outgassing in long-term storage, which is necessary for lifetime prediction of these materials.<br/>A filled PDMS, M9787, was investigated to get insight on the water interactions mechanism with temperature programmed desorption (TPD) and the first principles density functional theory (DFT) methods. Vacuum heat treatment of materials prior to application as it relates to long term outgassing was probed by a comparative study on M9787 with/without such treatment. The outgassing kinetic parameters were extracted using the isoconversional and/or the iterative regression methods where appropriate. The amount of water outgassing expected during long-term vacuum/dry storage of the materials is predicted from the extracted outgassing kinetics. Utilizing the kinetic models, it is predicted that ~20 % of the total moisture outgassing from untreated samples happens quickly within the first few hours under vacuum before the rate slows down substantially as shown in the Fig. 1. Moreover, DFT calculations of water interactions with a silica surface provide some insights into the structural motifs and activation energy barriers that contribute to these different kinetics parameters.

Understanding moisture outgassing kinetics of a silica reinforced polydimethylsiloxane using experimental and first-principles modeling

253rd National Meeting (2017)

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