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

Abstract

This study is focused on structural characterization of hybrid glasses obtained by consolidation of melting gels. The melting gels were prepared in molar ratios of methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) of 75%MTES-25%DMDES and 65%MTES-35%DMDES. Following consolidation, the hybrid glasses were characterized using Raman, 29Si and 13C Nuclear Magnetic Resonance (NMR) spectroscopies, synchrotron Small Angle X-Ray Scattering (SAXS) and scanning electron microscopy (SEM). Raman spectroscopy revealed the presence of Si-C bonds in the hybrid glasses and 8-membered ring structures in the Si-O-Si network. Qualitative NMR spectroscopy identified the main molecular species, while quantitative NMR data showed that the ratio of trimers (T) to dimers (D) varied between 4.6 and 3.8. Two-dimensional 29Si NMR data were used to identify two distinct types of T3 environments. SAXS data showed that the glasses are homogeneous across the nm to micrometer length scales. The scattering cross section was one thousand times lower than what is expected when phase separation occurs. The SEM images show a uniform surface without defects, in agreement with the SAXS results, which further supports that the hybrid glasses are nonporous.

Platinum free thermally curable siloxanes for optoelectronic application – synthesis and properties

“…26,[34][35][36][37] This leads to highly cross-linked structures, mainly consisting of regions with full condensed T 3 -T 3 units with D 2 , T 2 and D 1 groups connecting the edges of this regions. 38 In our studies the addition of DAS directly to the condensation reaction of TAS units leads to a less cross-linked and exible structure with T 1 , T 2 and T 3 units. Aer completion of the reaction the D 0 signals are not detectable anymore but D 1 end groups.…”

“…16 Comparable non vinyl containing but also curable sol-gel based materials are solid and cannot be processed at room temperature but also soen at higher temperatures. 26,[34][35][36][37][38] Generally viscosities of 10 000-300 000 mPa s respectively 3000-15 000 mPa s are required for the manufacturing of optoelectronic devices by moulding or dispensing processes. 27,28 Ageing experiment All prepared samples show an increasing absolute value of viscosity with long storage times at room temperature.…”

“…Comparable results were obtained for the inorganic-organic hybrid glasses obtained by the so-called melting gel approach. 38 Due to the fact that the very broad chemical shis of the [PhSi(OR) 3Àx ] and [MeSi(OR) 3Àx ] units were superimposed a quantitative determination was not expedient. The T 2 chemical shis of [PhSi(OR) 3Àx ] are located in the region of À66.À69 ppm.…”

“…Related materials described in literature reveal a signicant loss of DAS monomers or side products caused by the curing procedure shown by quantitative analysis of the 13 C MAS NMR data. 38 In the condensation process six and eight membered cyclosiloxanes can be formed and can evaporate at elevated temperatures. 38 Because these ring forming reactions are independent of the compositions used, we studied the evaporation gases of the precursor gel of sample 5 exemplarily by TG-FTIR coupling methods.…”

“…38 In the condensation process six and eight membered cyclosiloxanes can be formed and can evaporate at elevated temperatures. 38 Because these ring forming reactions are independent of the compositions used, we studied the evaporation gases of the precursor gel of sample 5 exemplarily by TG-FTIR coupling methods. Isothermal heating at 250 C for 4 h revealed a signicant mass loss immediately aer raising the temperature (Fig.…”