Network formation and thermal stability enhancement in evolutionary crosslinked PDMS elastomers with sol-gel-formed silica nanoparticles: Comparativeness between as-received and pre-hydrolyzed TEOS

Abstract Filler formation and crosslinking normally take place in PDMS/TEOS elastomers yielded via sol-gel technique, while a few was reported about the competitiveness between such phenomena. A combined rheological/thermogravimetric analysis was applied in this work varying the curing time (8, 24, 48, 72, and 168 h) to track and compare silica formation as well as three-dimensional elastomer networks in PDMS matrices treated with as-received and pre-hydrolyzed TEOS. It was found that use of pre-hydrolyzed TEOS facilitates nanosilica formation leading to in-situ formation of nanocomposites exhibiting higher thermal stability and mechanical properties, as compared with the reference elastomers prepared at stoichiometric ratio. Silica formation was detected by means of TEM. Experimental results showed that during the first 8 h of the reaction between PDMS and as-received TEOS a three-dimensional network was formed, while silica precipitation was dominant when PDMS was treated with pre-hydrolyzed TEOS. Tensile measurements reveal that silica precipitation in non-stoichiometric samples enhances tensile strength and elongation at break compared to the samples prepared at stoichiometric ratio, especially for samples cured with pre-hydrolyzed TEOS. Silica domain size was ca. 150 and 200 nm for the networks cured with TEOS and pre-hydrolyzed TEOS, respectively.