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Hydrolysis and condensation of alkylmethoxysilanes. Studied by means of the Langmuir-Blodgett technique and electron spectroscopy for chemical analysis
YKI – Ytkemiska institutet.
YKI – Ytkemiska institutet.
1995 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, 2652-2660 p.Article in journal (Refereed)
Abstract [en]

Hydrolysis and condensation reactions of octadecyltrimethoxysilane (C18TMS) and octadecyldimethylmethoxysilane (C1sDMMS) have been studiedby means ofthe Langmuir-Blodgetttechnique and electron spectroscopy for chemical analysis (ESCA). C18TMS can form linear two-dimensional polymers, while C1eDMMS forms only dimers. The polymerization/dimerization rate seems to increase in the sequence pH 5.6—11—1. At pH 11 the spread monolayer contracts when electrolyte is added and becomes less compressible. This indicates decreased electrostatic repulsion within the ionized monolayer and/or a higher level of polymerization/dimerization of the film molecules. C18DMMS could be compressed at pH 1 to a surface area of ~18 Å2, before the film enters a condensed phase. Constant surface pressure-area relaxation experiments indicate that a nucleation process takes place in the C18DMMS film at pH 1 for sr = 20 mN m-l. In contrast, the C1sTMS film at pH 1 was stable for more than 12 h at 40 mN m-l. When two subsequent compression steps are applied with a delay of 16 h the C18TMS films (pH 5.6 and 11) reproduced the condensed pH 1 film, with molecular areas of ~20 Å2, while the C18DMMS film (pH 5.6 and 11) was still in an expanded state. A condensed state in the two-dimensional film indicates good packing and strong cohesion forces between the hydrocarbon chains. The dimer-forming C1sDMMS will not achieve the same strong cohesion that we find in the fully polymerized C18TMS films. For the C1aTMS film at pH 11 a lowering of the barrier speed increased the polymerization rate, as observed by decreasing compressibility and decreasing areas per molecule for a given surface pressure. Langmuir-Blodgett films analyzed by ESCA confirmed these results.

Place, publisher, year, edition, pages
1995. Vol. 11, 2652-2660 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-27274OAI: oai:DiVA.org:ri-27274DiVA: diva2:1054278
Note
A1018Available from: 2016-12-08 Created: 2016-12-08Bibliographically approved

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