Organisation and connectivity in Silicon-based hybrid materials by sol-gel process
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Q3.2.1
Organisation and connectivity in Silicon-based hybrid materials by sol-gel process. Bruno BOURY, F. BEN and Robert J.P. CORRIU* UMR 5637, cc007 Université de Montpellier II Place E. Bataillon 34 000 Montpellier (France) Abstract: Organisation of silicon-based hybrid materials prepared by sol-gel of (MeO)3nSiMen-(C6H4)2-SiMen(OMe)3-n (n = 0, 1, 2) was evaluated and evidences the possibility of self-association of the macromolecular units at the sol step and reorientation process at the ageing step. Introduction Contrary to silica that is always amorphous when prepared by Sol-Gel, a self-organisation in silicon-based hybrid materials prepared by the same process has been recently demonstrated when they are prepared with precursors R[Si(OMe)3]n.1-3 Such short-range organisation is apparently governed by the kinetic of formation of the Si-O-Si bonds and by mechanical reorientation of the material during the ageing.4-7
x-(MeO)3MexSi
S iMex(OMe)3-x
Hydrolysis/polycondensation THF / 3x eq. H2O / 25ºC
x=0
x =1 Si
O Si O O
In acidic medium In basic medium HCl (3%) NaOH (4%) MHIHCl MHINaOHl
x=2
Me Si Me
Me Si
Si O O
Me Si O Me
In acidic medium HCl (3%) MHIIIIHCl
Me
In acidic medium In basic medium HCl (3%) NaOH (4%) MHIIHCl MHIINaOHl
x = 0 (I) ⇒ MHIHCl and MHINaOH ; x = 1 (II) ⇒ MHIIHCl and MHIINaOH; x= 2 (III) ⇒ MHIIIHCl
We look at materials prepared with precursors I-III by Sol-Gel process (Scheme1), because these solids have the same organic group but the connectivity at silicon (the number of Si-OSi bond = C) is different. Therefore it allows to investigate the effect of C on the anisotropy of the corresponding hybrid materials and its relation with the formation of the Si-O-Si network.
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Q3.2.2
Experimental part. Optical observations were performed on materials prepared in Teflon coated glass cell of 25mm x25mm x30micron.6 Birefringence measurements, other analyses and the synthesis of precursor I, II and III by a Calas-Dunogues method were performed according to previously reported procedures.8,9 Hydrolysis/polycondensation was performed under argon with deionised water (pH=6) with THF with HCl or NaOHas catalyst. The solution was kept without any stirring in order to let the gellation to occur in a non-agitated solution. The gel was allowed to stand 1 week and then crushed, washed with acetone (20 ml), diethyl ether (20 ml) and finally dried for 12 h at 100°C under vacuum (0.1 mm Hg). Preparation of the hybrid material HMI, HMII and HMIII. The stoechiometric amount of water was used for complete hydrolysis/polycondensation: 3 equivalents for I, 2 equivalents for II and 1 equivalent for III (Scheme 1). Part of the gellation mixture was introduced in glass cells for measuring birefringence by optical microscopy in polarised light.8,9 For I and II, the gellation times w
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