Analysis of silanes and of siloxanes formation by Raman spectroscopy

Abstract

The consecutive reactions of acid involved siloxane formation are firstly measured in bulk and analysed by Raman spectroscopy. Influencing factors, which can be identified as the chemical properties of the silanes, the silylium cations, and miscibility are pointed out by using a special technique. The procedure is based on a modified Raman sample cell, which allows a single-phase system with controlled water content to be systematically quantitatively monitored. Additional to the novel opportunity to analyse the acid "catalysed" condensation during the formation of polysiloxanes, this publication contains an alternated theoretical mechanism for sol-gel synthesis considering a restricted water content. A major aspect of this introducing study is a detailed analysis and identification of the relevant Raman vibrational bands and their origin on the hand of ten different organyltrialkoxysilanes (methoxy and ethoxy). The ability to determine the kinetics of the acid catalysed formation is demonstrated on homologous series of alkyltrimethoxysilanes.

OctTES/TEOS system for hybrid coatings: real-time monitoring of the hydrolysis and condensation by Raman spectroscopy

“…A small peak is observed at about 710 cm −1 (Fig. (d) and (e)): a recent work attributes this feature to the formation of partially or fully hydroxylated alkyl‐silane (for OctTES C 8 H 17 Si(OCH 2 CH 3 ) 3‐x (OH) x where 1 ≤ × ≤ 3) …”

Statistical contact angle analyses: ‘slow moving’ drops on inclining flat mono-aminopropylsiloxane surfaces

“…The reason of these measured differences is most likely a combination of preparation effects and effects of the bulk material on the contact angle. The differences in proposed formation kinetic of the siloxane layer in presence or absence of additional water and acid [23] leads to the assumption that a well ordered defect poor and a less ordered very thin layer of mono-(3-Aminopropyl)siloxane were prepared. Even the AFM measurements, as performed in this study, results in only slightly, nonsignificant difference in the standard deviations for both surfaces [compare to Supplementary Material].…”

“…Especially for the condensation of the silanes the effect of water and the activation by acids (from proton and anion) is of importance. A recent study [23] clearly demonstrated by kinetic analyses that water is essential to condensate the silanes to siloxanes. Hence, during the straightforward deposition of this 'dry' wafer surface only a very small amount of silane will be absorbed onto the surface.…”

“…From the reactivity relation in the cited study and the absence of an activating acid it can be concluded that the reaction to the siloxane itself proceed at a time after the deposition procedure in the desiccator. 2 For example, around 200 mg of acid-free bulk methyltriethoxysilane containing a sufficient amount of water (>2.5 mol%) is much less reactive (reaction time >70 h) than methyltrimethoxysilane (reaction time >2 h) [23]. The first step of the surface preparation of the test surface which is part of the Supplementary Material was cleaning with peroxomonosulphuric acid (H 2 SO 4 (conc.…”

Statistical contact angle analyses; “slow moving” drops on a horizontal silicon-oxide surface

“…This is as mentioned in the manuscript of special interest due to the different preferential motion direction and therefore the different effects of roughness, inhomogeneities and so on. At the moment we are looking forward to fabricate surfaces for example based on siloxane-coatings [18,24,25] with different contact angles, different surface structures, well defined and stable. (Note to the editor, eventually refereeing to submitted publication about APTES coated wafers submitted elsewhere, minor revisions.…”