The moisture outgassing kinetics of a silica reinforced polydimethylsiloxane

Abstract

A silica-filled polydimethylsiloxane (PDMS) composite M9787 was investigated for potential outgassing in a vacuum/dry environment with the temperature programmed desorption/reaction method. The outgassing kinetics of 463 K vacuum heat-treated samples, vacuum heat-treated samples which were subsequently re-exposed to moisture, and untreated samples were extracted using the isoconversional and constrained iterative regression methods in a complementary fashion. Density functional theory (DFT) calculations of water interactions with a silica surface were also performed to provide insight into the structural motifs leading to the obtained kinetic parameters. Kinetic analysis/model revealed that no outgassing occurs from the vacuum heat-treated samples in subsequent vacuum/dry environment applications at room temperature (∼300 K). The main effect of re-exposure of the vacuum heat-treated samples to a glove box condition (∼30 ppm by volume of H2O) for even a couple of days was the formation, on the silica surface fillers, of ∼60 ppm by weight of physisorbed and loosely bonded moisture, which subsequently outgasses at room temperature in a vacuum/dry environment in a time span of 10 yr. However, without any vacuum heat treatment and even after 1 h of vacuum pump down, about 300 ppm by weight of H2O would be released from the PDMS in the next few hours. Thereafter the outgassing rate slows down substantially. The presented methodology of using the isoconversional kinetic analysis results and some appropriate nature of the reaction as the constraints for more accurate iterative regression analysis/deconvolution of complex kinetic spectra, and of checking the so-obtained results with first principle calculations such as DFT can serve as a template for treating other complex physical/chemical processes as well.

Moisture outgassing from siloxane elastomers containing surface-treated-silica fillers

“…Silica-reinforced siloxane elastomers are of interest in many applications (medical, electronics, food, aerospace) [1][2][3][4][5][6][7] due to their tunable mechanical properties, as well as excellent thermal and chemical stabilities. 1,8 These materials are used as adhesives, potting agents, optical materials, and serve as structural materials for biocompatible applications. Recently, they have been employed as additively manufactured (AM) foams of tailorable compositions and engineering properties.…”

“…In addition, moisture outgassing may result in degradation of interfacial polymer structures, lead to material incompatibility in the system, and compromise the mechanical properties of composite materials. 1,16,17 Prior work has shown that the interaction of a silica filler surface and water dominate the sorption and outgassing processes 1,18 wherein the thermal and chemical history of the filler is directly associated with the activation energy barrier of water release. 1 We have recently developed a suite of 3D-printed siloxanes (LL50) wherein the reinforcing filler is a hydrophobically treated fumed silica, which can significantly lower the moisture content and subsequent outgassing from elastomers after compounding and cure in comparison with traditional siloxane rubbers.…”

“…1,16,17 Prior work has shown that the interaction of a silica filler surface and water dominate the sorption and outgassing processes 1,18 wherein the thermal and chemical history of the filler is directly associated with the activation energy barrier of water release. 1 We have recently developed a suite of 3D-printed siloxanes (LL50) wherein the reinforcing filler is a hydrophobically treated fumed silica, which can significantly lower the moisture content and subsequent outgassing from elastomers after compounding and cure in comparison with traditional siloxane rubbers. With the advancement of additive manufacturing (AM) technology towards next generation rubber foam manufacture, successful mitigation of moisture uptake and outgassing from elastomers like LL50 should allow for more stable long term properties in applications where excess moisture can lead to corrosion and degradation of sensitive components.…”

“…Comparison among these siloxanes confirms that a functionalized fumed silica surface mitigates moisture uptake and subsequent outgassing in dry/vacuum applications, when compared with previously reported siloxane rubbers. 1,16,18,22 RESULTS AND DISCUSSION Moisture outgassing from compression molded LL50 Compression molded non-porous siloxane rubber (LL50) samples were subjected to TPD experiments and signals were analyzed to extract kinetic parameters. Long term outgassing projections were then performed.…”

Dynamic Triple-Mode Sorption and Outgassing in Materials

“…We note that moisture uptake by Sylgard-184 was less than one tenth of the uptake by Zircar RS-1200 at the similar conditions. The relatively large uptake by Zircar RS-1200 can be attributed to the presence of an alumina ceramic matrix, which is known to be hydrophilic 7, 28–30 .

Figure 1Typical moisture uptake (in %) vs. time (in minutes) or water activity profile for Sylgard-184 and Zircar RS-1200. Panel a: moisture uptake (in %) vs. time for Sylgard-184 at 30 °C, Panel b: moisture uptake (in %) vs. time for Zircar Rs-1200 at 30 °C, Panel c: moisture uptake (in %) vs. water activity for Sylgard-184 at 20, 30, 40, and 50 °C, Panel d: moisture uptake (in %) vs. water activity for zircar RS-1200 at 30, 50, and 70 °C.

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