The sol-gel process and
materials
From molecule to material
,Overview: from molecule to material
Bottom-up approach: we start from the molecule (Å) to reach a material
(mm and beyond).
01 Molecular precursors 02 Hydrolysis
Alkoxides M(OR)n Creation of –OH groups
03 Condensation 04 Growth
Olation and oxolation Fractal or Euclidean?
05 Gelation 06 Drying
Sol, gel, gelation time Xerogel or aerogel
07 Shaping 08 Applications
Dip coating, spin coating Strengths and limits of the process
2
,Principle: from sol to gel, then to material
Soft chemistry: molecular precursors undergo hydrolysis then condensation at room temperature.
SOL
dispersion in a liquid
Colloidal route Polymeric route
Compact particles → particulate gel (weak interactions) Branched chains → cross-linked gel (strong bonds)
GEL
continuous network trapping the solvent
Powders Monoliths Coatings Fibres
drying, grinding bulk pieces thin films drawing from the sol
3
, Molecular precursors
Alkoxides: formula M(OR)ₙ, with an M–O–C bond.
R group (alkyl) OR group (alkoxy)
Organometallic compounds: M(R)ₙ, the carbon is bonded
directly to the metal (no oxygen).
methyl –CH₃ methoxy –OCH₃
The R group acts on oxygen through its electron-donating
effect and steric hindrance: it tunes the hydrolysis rate. ethyl –CH₂CH₃ ethoxy –OCH₂CH₃
n-propyl n-propoxy
iso-propyl iso-propoxy
n-butyl n-butoxy
sec-butyl sec-butoxy
The best known: TEOS iso-butyl iso-butoxy
Si(OEt)₄ tert-butyl –C(CH₃)₃ tert-butoxy –OC(CH₃)₃
tetraethoxysilane, also called tetraethyl orthosilicate
4
materials
From molecule to material
,Overview: from molecule to material
Bottom-up approach: we start from the molecule (Å) to reach a material
(mm and beyond).
01 Molecular precursors 02 Hydrolysis
Alkoxides M(OR)n Creation of –OH groups
03 Condensation 04 Growth
Olation and oxolation Fractal or Euclidean?
05 Gelation 06 Drying
Sol, gel, gelation time Xerogel or aerogel
07 Shaping 08 Applications
Dip coating, spin coating Strengths and limits of the process
2
,Principle: from sol to gel, then to material
Soft chemistry: molecular precursors undergo hydrolysis then condensation at room temperature.
SOL
dispersion in a liquid
Colloidal route Polymeric route
Compact particles → particulate gel (weak interactions) Branched chains → cross-linked gel (strong bonds)
GEL
continuous network trapping the solvent
Powders Monoliths Coatings Fibres
drying, grinding bulk pieces thin films drawing from the sol
3
, Molecular precursors
Alkoxides: formula M(OR)ₙ, with an M–O–C bond.
R group (alkyl) OR group (alkoxy)
Organometallic compounds: M(R)ₙ, the carbon is bonded
directly to the metal (no oxygen).
methyl –CH₃ methoxy –OCH₃
The R group acts on oxygen through its electron-donating
effect and steric hindrance: it tunes the hydrolysis rate. ethyl –CH₂CH₃ ethoxy –OCH₂CH₃
n-propyl n-propoxy
iso-propyl iso-propoxy
n-butyl n-butoxy
sec-butyl sec-butoxy
The best known: TEOS iso-butyl iso-butoxy
Si(OEt)₄ tert-butyl –C(CH₃)₃ tert-butoxy –OC(CH₃)₃
tetraethoxysilane, also called tetraethyl orthosilicate
4
