Melting Gel Films for Low Temperature Seals

Abstract

Melting gels are silica-based hybrid gels with the curious behavior that they are rigid at room temperature, but soften around 110°C. A typical melting gel is prepared by mixing methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). MTES has one methyl group substituted for an ethoxy, and DMDES has two substitutions. The methyl groups do not hydrolyze, which limits the network-forming capability of the precursors. To gain insight into the molecular structure of the melting gels, differential scanning calorimetry and oscillatory rheometry studies were performed on melting gels before consolidation. According to oscillatory rheometry, at room temperature, the gels behave as viscous fluids, with a viscous modulus, G″(t,ω0) that is larger than the elastic modulus, G′(t,ω0). As the temperature is decreased, gels continue to behave as viscous fluids, with both moduli increasing with decreasing temperature. At some point, the moduli cross over, and this temperature is recorded as the glass transition temperature Tg. The Tg values obtained from both methods are in excellent agreement. The Tg decreases from -0.3oC to -56oC with an increase in the amount of di-substituted siloxane (DMDES) from 30 to 50 mole %. A decrease of the Tg follows an increase of the number of hydrolytically stable groups, meaning a decrease in the number of oxygen bridges between siloxane chains.

Hybrid Sol–Gel Glasses with Glass‐Transition Temperatures Below Room Temperature

“…Most notably, the glass‐transition temperature increases from −29.6°C to −11.7°C. This is a significant increase in the glass‐transition temperature, indicating changes in the relaxation behavior of the melting gel structure . Other compositions were subjected to the same type of isothermal hold at a temperature near their consolidation temperature, and similar increases in the glass‐transition temperature were measured.…”

Thickness-properties synergy in organic–inorganic consolidated melting-gel coatings for protection of 304 stainless steel in NaCl solutions

“…For this reason, the main objective in this work is the preparation of new hybrid glass coatings based MTES and DMDES on stainless steel, which have a small thickness that can be easily applied as a single layer and is able to maintain excellent anti-corrosion properties. The main obstacle in obtaining thin coatings using the melting gels prepared using MTES and DMDES is the high viscosity of those gels [33]. In order to overcome this issue the melting gels were diluted with the parental solvent which allowed us to obtain coatings with a controlled thickness by dip coating.…”

29Si NMR and SAXS investigation of the hybrid organic–inorganic glasses obtained by consolidation of the melting gels

“…First, the melting gel with 75%MTES-25%DMES composition is the gel with the highest content of MTES which retains the melting properties 5 . On the other hand, the melting gel with 65%MTES-35%DMES composition is the borderline gel between solid and liquid state 11 at room temperature. Second, the hybrid organic inorganic glasses obtained using those compositions proved to be the best anticorrosive coatings 12 .…”

“…Mainly the focus was on preparation 5,9 using methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES), on their thermal stability 10,11 , and on their viscoelastic properties 11 . The hybrid glasses obtained from these melting gels were characterized by FT-IR and Raman spectroscopy 5,12 .…”