Heat treatment of commercial Polydimethylsiloxane PDMS precursors: Part I. Towards conversion of patternable soft gels into hard ceramics

The commercially available polydimethylsiloxane (Sylgard®184) is a commonly known material in microelectronic and microfluidic industries as flexible substrates, device packing elements, lab-on-a-chip, or stamps. Recently, PDMS derived materials have attracted much interest in the development of broadband electromagnetic absorbers in the terahertz and microwave regions. When exposed to high temperature (T > 900 °C) PDMS undergoes profound transformations leading to derived solid nanocomposites made of graphitic phase embedded into silicon oxycarbide structure. In this work, we discuss the PDMS thermal changes that have been evaluated using different analytical techniques (thermogravimetry-coupled mass spectrometry, and Raman spectroscopy). The pyrolysis of cross-linked gels in an inert atmosphere gave 50.94 wt% of solid residue at 1500 °C. It was observed that the presence of Si–H bonds in the curing agent promotes cross-linking between the siloxane backbones containing vinyl groups (Si–C2H3) through hydrosilylation reaction. However, excessive addition of curing agent impedes ceramic yield down to 20%. Above 1000 °C, Raman spectra show the formation of disordered sp2 carbon that subsequently organizes with the heat-treatment temperature. These carbon-rich silicon oxycarbide materials are remarkably resistance to oxidation even at 1500 °C.