MS512copy

Sol-Gel Nano Materials and Process

MS512 Nano Technology

Prof. Byeong-Soo Bae

Prof. Byeong-Soo Bae Dept. of Materials Sci. & Eng.

[email protected]

I. IntroductionII. Chemistry of Precursors SolutionsIII. Sol-Gel Process of SilicaIV. Sol-Gel Process of Complex Oxides

(Ferroelectrics)V. Sol-Gel Process of Hybrid MaterialsVI. Sol-Gel Process of Mesoporous

Materials

Text:1. A. C. Pierre, Introduction to Sol-Gel Processing, Kluwer Academic

Publisher, 19982. C. J. Brinker, G. W. Scherer, Sol-Gel Science, Academic Press,

1990

mailto:[email protected]

I. Introduction



• Sol-gel Processing

Sol-gel processing is a wet chemical route to synthesis of a colloidal suspension of solid

particles or clusters in a liquid (sol) and subsequently to formation of a dual phase material of

a solid skeleton filled with a solvent (wet gel) through sol-gel transition (gelation). When the

solvent is removed, the wet gel converts to a xerogel through ambient pressure drying or an

aerogel through supercritical drying. Thin (~ 100 nm), uniform and crack-free films can be

readily formed on various materials by dip, spin, or spray-coating; thick films can be obtained

by multiple coatings.

In the sol preparation, the precursors (either organic or inorganic) undergo two chemical

reactions: hydrolysis and condensation or polymerization, typically with acid or base as

catalysts, to form small solid particles or clusters in a liquid (either organic or aqueous

solvent). The solid particles or clusters are so small (1~1,000 nm) that gravitational forces are

negligible and interactions are dominated by van der Waals, coulombic and steric forces. Sols

are stabilized by an electric double layer, or steric repulsion, or their combination.

Colloid: a suspension in which the dispersed phase is so small ( 1~1000 nm) that gravitational forces are negligible and interactions are dominated by short-range forces, such as Van der Waals attraction and surface charges.



Sol: a colloidal suspension of solid particles in a liquid .

Gel: a solid network filled with a second phase of colloidal dimensions, either liquid or gas that also forms a three dimensional inter-connected network.

Gelation: also called sol-gel transition that begins with the formation of solid fractal aggregates that grow until they extends throughout the sol.

Xerogel: a gel in which the solvent has been removed by evaporation at an ambient environment.

Aerogel: a gel in which the solvent has been removed by supercritical drying. An aerogel typically has a porosity >75% and a BET surface area > 1000 m2/g.

Supercritical drying: a process of removing the liquid from the pores of wet gel above the critical temperature and critical pressure.

Precursor: a starting compound for preparation of a colloid (or sol). It consists of a metal or metalloid element surrounded by various ligands. It includes inorganic salts and organic compounds.

Hydrolysis: a chemical reaction in which hydroxyl groups become attached to the metal atom by replacing the ligands in the precursor.



Condensation (or polymerization): A process that hydroxyl groups merge to form metal- oxygen-metal bonds, while releasing a water molecule, resulting in formation of solid particles or clusters through combining monomers, growth of particles or clusters, and linking of particles or clusters into chains and networks that extend through the sol.

Steric force: a repulsion which results from polymers adsorbed to the interacting surfaces. The physical basis of the steric repulsion is a combination of a volume restriction effect arising from the decrease in possible configurations in the region between the two surfaces and an osmotic effect due to the relatively high concentration of adsorbed polymers in the region between the two surfaces as they approach one another.

Electric double layer: forms at the vicinity of a solid particle in a sol. When a solid submerges into a liquid, the surface will be electrically charged and subsequently an electric double layer forms due to the combination of coulombic, entropic and other specific forces. When two particles approach each other, as soon as the double layers overlap, a repulsive electrostatic force arises to prevent two solid particles to aggregate so that the sol is stabilized.

Sol-gel processing is a simple technology in principle but has required considerable effort to

become of practical use. Sol-gel enables materials to be mixed on an atomic level and thus

crystallization and densification to be accomplished at a much low temperature. However, a true

atomic level homogeneity in a multiple component system is an endeavor; the difficulty arises

from the fact that the chemical reactivity varies greatly from precursor to precursor. Precursor

modification and step-wise partial hydrolysis are the common approaches to homogeneity in

multiple component systems.

The advantages of the sol-gel process in general are high purity, homogeneity, and low

temperature. For a lower temperature process, there is a reduced loss of volatile components and

thus the process is more environmental friendly. In addition, some materials that cannot be made

by conventional means because of thermal and thermodynamical instability, can be made by this

process. The sol-gel process has many applications in synthesis of novel materials. Examples

include aerogels used in space crafts to capture stellar dust, xerogels as matrix in biosensors, and

high power laser materials.



Condensation

RO OH

OR

OR

M RO OR

OR

OR

M RO O

OR

OR

M+ OR

OR

OR

M

RO OH

OR

OR

M HO OR

OR

OR

M ROO

M

OR OR

+ HOH

OR

OR

M+

OR

+ ROH

Hydrolysis

RO OR + H

2O

OR

OR

M RO OH

OR

OR

M + ROH

Alkoxides:M(OR)n M= Si,Ti,Zr,Al

R= -CH3, -CH2CH3



•Definitions of Sol-Gel Process

Alkoxide Sol-Gel

• Dislich - Procedure to prepare the multicomponent oxides that are homogeneous at the atomic level� should include the colloidal coprecipitates of hydroxides and oxyhydrates� restrict to the gels synthesized from metal alkoxides

Coloidal Sol-Gel

• Segal – Production of inorganic oxides either from colloidal dispersion or from the metal alkoxides

� non-oxides such as nitrides and sulfides, and organic-inorganic hybrids

• Colloidal route used to synthesize ceramics with an intermediate stage including a sol and/or gel state

• Production of inorganic oxides either from colloidal dispersion or from the metal alkoxides

• Chemical processing to synthesize ceramics glasses, and hybrids from wet chemicals



• Inorganic Polymerization

Monomer

Solution

Dimer Oligomer

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O

Sol

Gel

O

M OO M

O

O M

O

O

O

M

O

OO M

O

O

O M

O

O

O

O O O

O M O O M O M O

O O O

M OO M O M O M M

O

OO M

O

O

O

M

O

OO M

O

O

O M

O

OO

O M

O

O M O

O

M

O

O

O

M OO M

O

O M

OOxide

O M

O O

M OO M

O

O

M

O

OO M

O

O M

O

O M

O

O M O

O

M

O

O

Solid

ColloidGelation



DryingSintering

Processing of Sol-Gel Materials

• Powders

• Monoliths

• Fibers

• Coatings and Thin Films



• Porous Materials and Aerogel

Melting and Sol-Gel Process for Glass Fabrication



Advantages and Disadvantages of Sol-Gel Process



• Advantages • Disadvantages

High purity from raw materials High cost of raw materials

Good homogeneity from raw materials Large shrinkage during processing

Low processing temperature Residual fine pores and hydroxyls

Good shape ability Health hazards of organic solution

Production of new composition glasses Easily cracking during the drying stage

Long processing times

Characteristics of Sol-Gel Process



D Low temperature process of fine ceramics and glasses

D Bottom-up fabrication from chemicals

D Aqueous-based chemistry and process

D Immobilization & encapsulation over wide range of sizes, chemistries and functions

D Mild & easily controlled conditions

D Molecular level dispersion

Fabrication of Sol-Gel Optical Fiber Preform

정화소결

혼합 및 캐스팅 탈착 건조



Sol-Gel Coatings on Display

Silica layerAR layers

CCoonndduuccttiivvee layer

GlassLight

1.0% of incident light<Interference effect>

Antiglare

R G B

Phosphor



• Preparation of Nano Materials by Sol-Gel Processing

Solution Glass, Ceramics

Heated gel

Sol Dry gel

Wet gel졸 - 겔 생성물

Porous gels

Pores

Gels dispersed with organic

molecules

Inorganic- organic

composites

CeramicsGlassGels dispersed with inorganic or metal particles

Organic moleculesOrganic polymer Inorganic network

Particles

Grains

<100C

<150C

<500C

<1200C

<100C

미세구조



나노구조재 나노하이브리드 나노복합체나노복합체

II. Chemistry of Precursors Solutions

Precursor Solution

• Chemical PrecursorChemical reactant which contain the cation M present

in the final inorganic sol or gel

Metallic salts - MmXn, eq) AlCl3

Metal alkoxides – M(OR)n, eq) Al(O Organometalic compounds

• SolventsWaterNon-aqueous solution

Protic solvent Aprotic solvent

Acidic solvent Basic solvent Amphoretic solvent

C2H5)3



Hydrolysis of Metal Salts Solution

• Ions SolvationDissolution is solution

MX � Mz+ + Xz- in the solution

Cation solvationSolvatation shell [M(H2O)N]Z+

• HydrolysisDeprotonation of a solvated metal cation

Aquo ligand H2O � hydroxo ligand(OH-)or an

• Formation of Hydroxo LigandsSolvated metal: an acid, Water: Lewis base

[M(OH2)N]Z+ + hH2O ⇔ [M(OH)(OH2)N-1](z-1) + + H3O+

acid + Lewis base ⇔ conjugates base conjugated acid

[M(OH)h(OH2)N-h] “aquo-hydroxo” complex

oxo ligand(O2-)



• Formation of Oxo LigandsDeprotonation of an hydroxo ligand

[M(OH)(OH2)N-1](Z-1)+ + hH2O ⇔ [MOh(OH2)N-h] (Z-h)+ + hH3O+

acid+ Lewis base ⇔ conjugated base + conjugated acid

[MO(OH2)N-1]z-2 “aquo-oxo ligand “ complex

[M(OH2)N]Z+ + hH2O ⇔ [M(OH)(OH2)N-1](z-1) + + H3O + hH2O ⇔ [MOh(OH2)N-h] (Z-h)+ +

hH3O+



h=0 : [MONH2N]Z+

aquo-ion0<h<N :

[M(OH)X(OH2)N-x](Z-X)+

hydroxo-aquo complex

h=N : M(OH)N](N-Z)-

hydroxo complex N<h<2N : [MOX(OH)N-x](N+X-Z)-

oxo-hydroxo complexh=2N

: [MON](2N-Z)-

oxo-ion

Condensation of Metal Salt Solution

• Condensation and PolymerizationHydroxo ligand (M-OH) � “ol” bridge (M-OH-M) � “oxo” bridge (M-O-M)

• Condensation by OlationFor the low charge cations – dissociative SN1 mechanism

H2OM ⇔ -M- + H2O -M-OH + -M- ⇔ M-OH-M-

For the higher charge cations – nucleophilic addition reaction AN

-M-OH + -M-OH ⇔ M-OH-M-OH

For the transition elements – associative SN2 mechanism



• Condensation by OxolationFor the low charge cations – dissociative SN1 mechanism

H2OM ⇔ -M- + H2O -M-OH + -M- ⇔ M-OH-M-

For the higher higher charge cations – nucleophilic addition reaction AN

-M-OH + -M-OH ⇔ M-OH-M-OH

For the transition elements – associative SN2 mechanism



Alkoxide PrecusorsAlkoxides:M(OR)n M= Si,Ti,Zr,Al

R= -CH3, -CH2CH3



Hydrolysis of Metal Alkoxides

• HydrolysisAlkoxy group (OR) � Hydroxo(OH) or Oxo(O) ligands

(1) Nature of alkoxy group(2) Nature of solvent

(3) Concentration in solvent

(4) ) Water to alkoxide molar ratio rw = [H2O]/[alkoxide]

(5) temperature

• Formation of Hydroxo Ligands M(OR)z + H2O M(OH)(OR)z-1 + ROH



• Hydrolysis of Silicon AlkoxideAcidic solution (pH < 2.5)

- Negatively charged particles- [H3O]+ attack the oxygen in alkoxy group

• Formation of Oxo Ligands Lewis base Water vapor

Basic solution (pH > 2.5)- Positively charged particles- OH attacks the Si in alkoxides



-

Condensation of Metal Alkoxides

• Condensation by Olation SN2 nucleophilic substitution mechanism -

• Condensation of Oxolation Transfer of the H to an OR ligand Transfer of the H to an OH group



• Condensation of Silicon Alkoxides Acidic solution (pH < 2.5)

- Two – step SN2 type mechanism condensation- Protonation of silanol group- Hydrolysis is faster than condensation- Linear polymer

Basic solution (pH > 2.5)- Deprotonation of silanol group- Condensation is faster than hydrolysis- Dense solid



Precursor Mixing

• Mixing Two Alkoxides Double alkoxides

- Mixing two alkoxides in same non-aqueous solvent

Simultaneous hydrolysis of simple alkoxides- Simultaneous refluxing in solvent

Matching the hydrolysis rates of different alkoxides- Partially hydrolyzed Si(OR)4 and Al(OR’)3

• Mixing Two Metal Salts

• Mixing a Alkoxide with a Metal Salt



III. Sol-Gel Process of Silica1



1 Aqueous Silicate



Kinetics of hydrolysis and condensation is slower

• Polymerization at pH 2 - 7Proportional to [OH-]3-D gel network by aggregationHydrolysis with water

• Polymerization above pH 7 - 10Stable solParticle growth rather than aggregationThermal decomposition

• Polymerization below pH 2Proportional to [H+]Metastable

1 Silicon Alkoxide Sol-Gel

hydrolysis

estrification

alcohol condensation

Si- OR + H 2O

Si- OH + ROH

alcoholysis

water condensation

S i- O R + HO- Si Si- O- Si + ROH

hydrolysis

S i- O H + HO- Si Si- O- Si + H 2O

• Precursor Solution

Silicon alkoxide + water + alcohol + catalyst

H2O:Si molar ratio (r) – 1~ over 50

Concentrations of acids or bases – 0.01 ~ 7 M



• Tetraalkoxysilanes Si(OR)4 : TEOS(tetraethoxysilane),

TMOS(tetramethoxysilane)

• Organoalkoxysilanes R‘nSi(OR)3 : MTMS(Metyltrimethoxysilane),

DMDMS(Dimetyldimethoxysilane)



Precursor Molecules

• Molecular Building Blocks Hexamethoxydisiloane

OctamethoxytriethoxtsilaneMethoxylated cubic octamer - Silsiquioxane

1 Hydrolysis of Silicon Alkoxides

• Effects of Catalyst

• H2O/Si Ratio (r)



1 • Steric and Inductive Effects

• Effects of Solvents Protic solvent enhance hydrolysis



1 Condensation of Silicon Alkoxides

• Effect of Catalyst Minimum at about pH 1.5

Maximum at intermediate pH Acid catalyzed

condensation (pH<2)– protonated silanol

Base catalyzed condensation (pH>2)

– deprotonated silanol

• Steric and Inductive Effects

Acidity of silanol – higher pH IEP

Basicity of silanol – lower pH IEP

In acid-catalyzed,steric effects > inductive effects

• Effects of Solvent Protic solvent – acid-

catalyzed condensation Aprotic solvent – base-

catalyzed condensati

on



1 Structural Summary

• Low pH ConditionHydrolysis rate > condensation rateCluster-cluster growth – network structure

• High pH ConditionUnhydrolyzed monomersMonomer-monomer growth - particles

• Intermediate pH ConditionMinimum hydrolysis rate – rate limiting

• General Condition Acid catalyzed, low water system – drawing fiber Acid catalyzed, high-water system – bulk gels Base catalyzed, high-water system – particles



1

Sol-Gel Ferroelectrics

• Metallorganic PrecursorsMetal alkoxides

Zr n-propoxide [Zr(OC3H7)4]Ti isopropoxide [Ti(OCH(CH3)2)4] Ethoxides, Butoxides

Inorganic or organic salts La nitrate

Pb acetate

• SolventsPrimary solvent - stablization

Chemical modifiers-methoxyethanol, acetic acid glycol

Chelating agents- -diketone (acetylacetone)

Secondary solventEthylene glycol, propanol, methanol or water Control in viscosity, pH, surface tension

Lead Titanium Zirconium

Gelation Control Firing Additives

Viscosity Adjustment

Precursor Solution

Dipping,Spraying or Spin Coating

Crystallization 400-700 ºC

Drying and Organic Removal280-400ºC

Multilayer Coatings

Alcohol or Water

IV. Sol-Gel Process of Complex Oxides



• Solution Process of Electo or Optical Ceramics

1



Preparation of Ferroelectric Solutions

• Alcohol-Based SolutionPb acetate trihydrate, Ti isopropoxide, Zr n-propoxide2-methoxyethanol + 2-methoxyethanol/waterChange to methoxides and partial hydrolysis

• Water-Based SolutionPb acetate trihydrate, Ti isopropoxide, Zr n-propoxideAcetic acid + water, propanol, glycolsHydrolysis with water

• MOD SolutionPb acetate, Ti acetylacetonate, Zr acetate

Pb 2-ethyl hexanonate, Ti isopropoxide, Zr tetra-n-butoxideWater + methanol, hexaneThermal decomposition

Fabrication of Ferroelectric Films

Sr metal Ba metal

2-Methoxyethanol 2-Methoxyethanol

0.4M precusor solution

Drying

2-Methoxyethanol

DistillationTi isopropoxide

Coating

Heat Treatment for Crystallization

Iteration

In dry N2 gas

Coating

Drying

Heat Treatment for Crystallization

Nb(OC2H5)5

2-Methoxyethanol

Iteration

Refluxing (12h)

0.1M SBN sol



Distillation

Refluxing

Preparation of Stable Solution

• Dilution

Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide

2-methoxyethanol + 2-methoxyethanol/water

Change to methoxides and partial hydrolysis

• Chemical Modification and Complexation

Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide

Acetic acid + water, propanol, glycols

Hydrolysis with water

• Surface Modification of Nanoparticles

Stablization of particles



IV. Sol-Gel Process of Hybrid Materials

size 분산상의 크기

mm

m

1nm

1Å

복합재료

폴리머 / 폴리머 유리입자 / 폴리머 유리섬유 / 폴리머

세라믹 / 폴리머 금속 / 폴리머 세라믹 / 금속

(FRP,FRC,FRM)

Nanocomposite

Nanohybrid

물리적 혼합

물성은 복합 법칙에 따름

복합법칙에 따르지 않는 새로운 물성이

발견됨

수소결합 화학결합

신물성

Physical

hybridization



hybridization

Class I (Nanocomposite)D Organic dyes embedded in sol-gel matrix

Organic dyes, inorganic ions or molecules + silica, aluminosilicate, zirconia, titania

� fluorescence, photochromic, non-linear optical properties

D Inorganic particles embedded in a polymer

Inorganic particles + polymer blend



D Organic monomers embedded in sol-gel matricesPolymerizable organic monomer + sol-gel inorganic matrices

Polymerization

Sol-gel

D Polymers filled with in-situ generated inorganic particles

Inorganic particle formation by sol-gel reaction in a polymer matrices

Sol-gel



Polymerization

D Simultaneous formation of interpenetrating organic-inorganic networks

Alkoxides functionalized by liable plymerizable group

Sol-gel

Polymerization



D Obtension of ordered organic-inorganic structures

Insertion of organic molecules polymers into an anisotropic inorganic network

Build anisotropic inorganic particles using organic molecules and self assembled aggregates

Sol-gel





Class II (Nanohybrids)

D Organically modified silicon alkoxides

R’xSi(OR)

4-x

Polymerization

Sol-gel

D Polyfunctional alkoxysilanes

(RO)3Si-R’-Si(OR)3

Sol-gel



D Alkoxysilanes functionalized by polymers(RO)3Si-Polymer-Si(OR)3

Sol-gel

D Surface modification by organoalkoxysilanes

Polymerization



D Template building blocks

Polymerization

D Ordered hybrid materialsSelf-assembly of molecular units on surface hydroxyl groups



Hybrids from Sol-Gel Process of Organoalkoxysilanes

Network modifier ( R' : unreactable)

CnH2n+1-Si(OR)3

Si(OR)3

H2N-(CH2)3-Si(OR)3

CF3-(CF2)n-(CH2)2-Si(OR)3

methyl, ethyl

phenyl

amino

fluoro

Network former ( R' :polymerizable)

H2C CH-O-(CH2)3-Si(OR)3

Oepoxy

O

O-(CH2)3-Si(OR)3methacrylate

HS-(CH2)3-Si(OR)3

C Si(OR)3

H2C

H

mercaptopropyl

vinyl

R

R

R inorganic

= O

= Si,Ti,Zr,...modifier

entrapped molecule

R

organic polymeric chain

Modification Functionalization

Crosslinking

R’nSi(OR)4-n



D Compensation of Characteristics

Y Hard and Stable Y Soft and Flexible Y Easy ProcessY Cheap

D Functionalization Y Modification Y New function

D TransparencyY Optical materialsY Functional coating

Silica Network

Polymer Network

Heterometal NetworkOrganic Modification

ORMOCER, CERAMER, POLYCERAM,Hybrid Sol-Gel Glass, Hybrid Polymer, HYBMRIMER

ORMOCER, CERAMER, POLYCERAM,Hybrid Sol-Gel Glass, Hybrid Polymer, HYBMRIMER

Sol-Gel Hybrid Materials (HYBRIMER)



Characteristics of HYBRIMERD Transparency

D Functionality

D Compensation of Characteristics

D Modulation & Tunability of Characteristics

D Easy Process & Fabrication

D High Thermal & Chemical Stability

D Easy Encapsulation with Better Compatibility



Transparency of HYBRIMERD Hybrids of molecular level

D Coloration by doping of dyes or colloids

D Application of optics, display, and coatings



Compensation of Characteristics

Ref.: Fraunhofer ISC



Compensation of Characteristics

D Compensation of Polymer and Glass Properties

High

Low

Hardness

450 -950

90 -250

Thermal Stability

1.35 – 1.95

High

-8 to 6

-10 to 160

4 -130

1.40 - 1.65

Low

-140 to -85

150 to 700

1 -10

Refractive index

Dielectric Constant

dn/dT (10-7℃)

Thermal Expansion

Young’s Modulus

(Mpa)

Glass

Polymers



Compensation of CharacteristicsD Mechanical Properties Silica/PDMS

HYBRIMER



Functionality of HYBRIMERD Hydrophilic and Hydrophobic

Coatings



Optical Application of HYBRIMERD Solid state dye laser materials

D Rare-earth emission materials

D Nonlinear optical and photorefractive materials

D Photochemical hole burning materials

D Photochromic materials

D Optical sensor matrials

D Optical waveguide materials



Functionality of HYBRIMER

Unpoled Polymers

Poled Polymers

amplitude, wave form E-O Modulators

• heating around Tg• electric field on• cooling• electric field off

SHG

EO

EOspatial, wave frontSpatial Light Modulators

wave length change Frequancy Doubling

(a)

(b)

(c)

Unpoled Sol-Gel Hybrids

Poled Sol-Gel Hybrids

이광섭 교수 , 한남대

HC

l / DM

F- C

H3 O

H

- H2 O

D NLO Chromophore HYBRIMER

(OEt)3Si Si(OEt)3

NL

O

O O

Si

O

O



O

Si

Si

O OO Si

O

Si

OSi

Si

OO OO

Si

OO

SiSi

O

SiO O

SiO

Si

O

O

Si

Si O

O

Si O O

O Si

O

Si

Si

O

O O

O

Si

O

Si

OO O

SiO

NLO

NL

O

NLO

NL

O

NLO

NLO

NL

O

NLO

NL

O

NL

O

NLO

NLO

Silica vs. Polymer forWaveguide Materials

SSiill

iicca

a

PPoolly

ymmee

rr

Spin-on Low

temp. Easy, Cheap

Versatile

FHD,CVDHigh temp

Difficult,Expensive.

Process

Absorption Mechanical Thermal

Lowe

r

Hig

h

Hig

h

Lo

w

Lo

w

Lo

w

Thermo-optics Design

Functionality

High

Versati

le

Versati

le

Lo

w

No

t

No

t

Polarization dependence



Stress

Anisotropy

Advantages of HYBRIMER Waveguide

Silica Waveguide

Sol-Gel Silica Waveguide

Manipulation of refractive index in a broad range Easy fabrication

Easy incorporation of inorganic/organic doponts

HYBRIMER Waveguide

Manipulation of refractive index in a broad range

Thermally and chemically stable

Hardness for end facet polishing

Thick films without cracks Hydrogen bonding to stabilize

organic dopants

Photoimprinting, Easy process

Polymer Waveguide



Micro-Patterning in HYBMRIMER by Photo-polymerization

Photoh-initiator

R'=CH3;C2H4OH= - C3H6OOC -

Selective etchingUV

developing

Fabrication of waveguides



Encapsulation & Immobilization in HYBRIMERD Entrapment of biomolecules and chemical species in

porous structureD Better compatibility in organic environmentsD Applications in biosensor, bioreactors, chemical sensor, catalysis



VI. Sol-Gel Process of Mesoporous Materials• Micelle Structure

Spherical micelle

Cylindrical micelle

Lamellar micelle

Inverse micelle



• Ordered Mesoporous Materials Hexagonal packing of cylindrical micelles Cubic packing of spherical micelles Planar packing of micellar micelles

• Fabrication Procedure Micellar rods with a surfactant � micelles in a hexagonal array � add inorganic

precursor solution in a polar solvent � array of hollow oxide cylinders – organic

heart elimination by washing or by calcination

Micelles with inorganic precursor solution

HexagonalCubic



LamellarCubic

• Surfactants Alkyl-ammonium halide (cationic surfactant)

[CnH2n+1N(CH3)3]X- , X=Cl or Br Cetyltrimethylammonium bromide (CTAB)

Poly(oxyethylene) non-ionic surfactant [n-alkylpolyethylene glycol ethers]

CH3(CH2)n-1(OCH2CH2)mOH = CnEOm Brij 56, C16H33(OCH2CH2)10OH

Poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)





• Pure Silicate CompositionLiquid Crystal Templating Mechanism• Silica source – TEOS, Ludox, fumed silica, sodium silicate

Alkyltrimethylammonium halide surfactant - cetyltrimethylammonium bromide (CTAB)

Base - sodium hydroxide or tetramethylammonium hydroxide (TMAOH)Water

Silicate Rod Assembly



Silicate Layer Puckering Charge Density Matching

Folding Sheets



Silicatropic Liquid Crystals



General Liquid Crystal Templating Mechanism: Electrostatic Mechanism



• Applications Catalysis

- High Surface Areas and Thermal Stability Sorption and Separation Inclusion of Nanostructured Materials Optical Applications

- Dye Inclusion

- Nanocrystals (Quantum Dots)

- Organometallic Complexes

- Polymer Inclusions

- NLO and Laser Materials

- Photochromic Materials Chemical Sensors

Insulator Materials

Low k Materials Hydrogen Storage and Electrode Materials

- Carbon Nanotubes



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