MS512copy

Prof. Prof. ByeongByeong--Soo BaeSoo Bae MS512 MS512 Nano Nano TechnologyTechnology

Sol-Gel Nano Materials and ProcessProf. Byeong-Soo Bae

Dept. of Materials Sci. & [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


I. IntroductionSol-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 Waalsattraction 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 RO O

OR

OR

M+ OR

OR

OR

M

+ ROH

+ HOH

Hydrolysis

RO OR

OR

OR

M RO OH

OR

OR

M+ H 2O + 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 oxyhydratesrestrict 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 hybridsColloidal 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

O

M

O

OO

Solution

Dimer

O

M

O

OO M

O

O

O

Oligomer

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O

Sol

Gel

O

M

O

OO M

O

O

O M

O

O

O

O

M

O

OO M

O

O

O M

O

O

O

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O

O

M

O

OO M

O

O

O

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O M O

O

M

O

O

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O

O

M

O

OO M

O

O

O

O

M

O

OO M

O

O

O M

O

O

O M

O

O

O M O

O

M

O

O

Solid

ColloidOxideGelation

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

♦High purity from raw materials

♦Good homogeneity from raw materials

♦Low processing temperature

♦Good shape ability

♦Production of new composition glasses

Disadvantages

♦High cost of raw materials

♦Large shrinkage during processing

♦Residual fine pores and hydroxyls

♦Health hazards of organic solution

♦Easily cracking during the drying stage

♦Long processing times


Characteristics of Sol-Gel Process

Low temperature process of fine ceramics and glasses

Bottom-up fabrication from chemicals

Aqueous-based chemistry and process

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

Mild & easily controlled conditions

Molecular level dispersion


Fabrication of Sol-Gel Optical Fiber Preform

정화정화소결소결

혼합혼합 및및 캐스팅캐스팅 탈착탈착 건조건조


Sol-Gel Coatings on Display

GlassGlass

ConductiveConductivelayerlayer

Silica layerSilica layer

LightLight

1.0% 1.0% of incident lightof incident light<Interference effect><Interference effect>

AntiglareAntiglare

RR GG BB

PhosphorPhosphor

AR layersAR layers


Preparation of Nano Materials by Sol-Gel Processing

Solution Glass, Ceramics

Heated gelSol Dry

gelWet 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

ParticlesGrains

<100°C <150°C <500°C <1200°C<100°C

미세구조

나노구조재 나노하이브리드 나노복합체나노복합체


II. Chemistry of Precursors SolutionsPrecursor Solution

Chemical Precursor♦Chemical reactant which contain the cation M present

in the final inorganic sol or gel

♦Metallic salts - MmXn, eq) AlCl3Metal alkoxides – M(OR)n, eq) Al(OC2H5)3Organometalic compounds

Solvents♦Water♦Non-aqueous solution

♦Protic solventAprotic solvent

♦Acidic solventBasic solventAmphoretic solvent


Hydrolysis of Metal Salts Solution

Ions Solvation♦Dissolution is solution

MX Mz+ + Xz- in the solution

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

Hydrolysis♦Deprotonation of a solvated metal cation

Aquo ligand H2O hydroxo ligand(OH-)or an oxo ligand(O2-)

Formation of Hydroxo Ligands♦Solvated 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


Formation of Oxo Ligands♦Deprotonation 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 complexh=N : M(OH)N](N-Z)-

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

oxo-hydroxo complexh=2N : [MON](2N-Z)-

oxo-ion


Condensation of Metal Salt SolutionCondensation and Polymerization♦Hydroxo ligand (M-OH) “ol” bridge (M-OH-M) “oxo” bridge (M-O-M)

Condensation by Olation♦For 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 Oxolation♦For 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

Hydrolysis♦Alkoxy 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 Alkoxide♦Acidic 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 Silica17


17Aqueous Silicate

♦Kinetics of hydrolysis and condensation is slower

Polymerization at pH 2 - 7♦Proportional to [OH-]♦3-D gel network by aggregation♦Hydrolysis with water

Polymerization above pH 7 - 10♦Stable sol♦Particle growth rather than aggregation♦Thermal decomposition

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


17Silicon Alkoxide Sol-Gel

hydrolysis

estrification

Si- OR + H2O Si- OH + ROH

alcohol condensation

alcoholysis

Si- OR + HO- Si Si- O- Si + ROH

water condensation

hydrolysisSi- OH+ HO- Si Si- O- Si + H2O

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


17Hydrolysis of Silicon Alkoxides

Effects of Catalyst

H2O/Si Ratio (r)


17 Steric and Inductive Effects

Effects of Solvents♦ Protic solvent enhance hydrolysis


17Condensation 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 condensation


17Structural Summary

Low pH Condition♦Hydrolysis rate > condensation rate♦Cluster-cluster growth – network structure

High pH Condition♦Unhydrolyzed monomers♦Monomer-monomer growth - particles

Intermediate pH Condition♦Minimum 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


16

Sol-Gel FerroelectricsMetallorganic Precursors♦Metal alkoxides

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

♦Inorganic or organic saltsLa nitratePb acetate

Solvents♦Primary solvent - stablization

Chemical modifiers- methoxyethanol, acetic acid glycol

Chelating agents- β-diketone (acetylacetone)

♦Secondary solventEthylene glycol, propanol, methanol or waterControl in viscosity, pH, surface tension

Lead Titanium Zirconium

Gelation Control Firing Additives

Viscosity Adjustment

Precursor Solution

Dipping,Sprayingor Spin Coating

Crystallization400-700 ºC

Drying and Organic Removal280-400ºC

Multilayer Coatings

Alcohol or Water

IV. Sol-Gel Process of Complex OxidesSolution Process of Electo or Optical Ceramics


17Preparation of Ferroelectric Solutions

Alcohol-Based Solution♦Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide♦2-methoxyethanol + 2-methoxyethanol/water♦Change to methoxides and partial hydrolysis

Water-Based Solution♦Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide♦Acetic acid + water, propanol, glycols♦Hydrolysis with water

MOD Solution♦Pb acetate, Ti acetylacetonate, Zr acetate

Pb 2-ethyl hexanonate, Ti isopropoxide, Zr tetra-n-butoxide♦Water + methanol, hexane♦Thermal decomposition


Fabrication of Ferroelectric Films

Sr metal Ba metal

2-Methoxyethanol

Nb(OC2H5)5

2-Methoxyethanol

La nitrate Pb acetate

22-Methoxyethanol

0.4M precusor solution

Drying

2-Methoxyethanol

Distillation Distillation Ti isopropoxide

Coating

Heat Treatmentfor Crystallization

Iteration

In dry N2 gas

Coating

Drying

Heat Treatmentfor Crystallization

Iteration

Refluxing Refluxing (12h)

0.1M SBN sol


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

mm

µm

1nm

1Å

분산상의 크기

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

신물질

신물성

Physical hybridization

Chemical hybridization


Class I (Class I (NanocompositeNanocomposite))Organic dyes embedded in sol-gel matrixOrganic dyes, inorganic ions or molecules + silica, aluminosilicate, zirconia, titania

fluorescence, photochromic, non-linear optical properties

Inorganic particles embedded in a polymerInorganic particles + polymer blend


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

Polymerization

Sol-gel

Polymers filled with in-situ generated inorganic particlesInorganic particle formation by sol-gel reaction in a polymer matrices

Sol-gel

Polymerization


Simultaneous formation of interpenetrating organic-inorganic networksAlkoxides functionalized by liable plymerizable group

Sol-gel

Polymerization


Obtension of ordered organic-inorganic structuresInsertion of organic molecules polymers into an anisotropic inorganic network

Build anisotropic inorganic particles using organic molecules and self assembled aggregates

Sol-gel



Class II (Class II (NanohybridsNanohybrids))

Organically modified silicon alkoxides R’xSi(OR)4-x

PolymerizationSol-gel

Polyfunctional alkoxysilanes (RO)3Si-R’-Si(OR)3

Sol-gel


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

Sol-gel

Surface modification by organoalkoxysilanes

Polymerization


Template building blocks

Polymerization

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


Hybrids from SolHybrids from Sol--Gel Process ofGel Process of OrganoalkoxysilanesOrganoalkoxysilanes

Network modifier ( R' : unreactable)

CnH2n+1-Si(OR)3 methyl, ethyl

Si(OR)3 phenyl

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

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

Network former ( R' :polymerizable)

H2CO

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

O

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

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

CH2C

HSi(OR)3

mercaptopropyl

vinyl

R

R

R

= O= Si,Ti,Zr,...inorganicmodifierentrappedmolecule

Rorganicpolymericchain

ModificationFunctionalization Crosslinking

RR’’nnSiSi(OR)(OR)44--nn


Compensation of CharacteristicsHard and StableSoft and FlexibleEasy ProcessCheap

FunctionalizationModificationNew function

TransparencyOptical materialsFunctional 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

SolSol--Gel Hybrid Materials (HYBRIMER)Gel Hybrid Materials (HYBRIMER)


Characteristics of HYBRIMERCharacteristics of HYBRIMERTransparency

Functionality

Compensation of Characteristics

Modulation & Tunability of Characteristics

Easy Process & Fabrication

High Thermal & Chemical Stability

Easy Encapsulation with Better Compatibility


Transparency of HYBRIMERTransparency of HYBRIMERHybrids of molecular level

Coloration by doping of dyes or colloids

Application of optics, display, and coatings


Compensation of CharacteristicsCompensation of Characteristics

Ref.: Fraunhofer ISC


Compensation of CharacteristicsCompensation of Characteristics

Compensation of Polymer and Glass Properties

HighLowHardness

450 -95090 -250Thermal Stability

4 -1301 -10Young’s Modulus (Mpa)

-10 to 160150 to 700Thermal Expansion

-8 to 6-140 to -85dn/dT (10-7℃)

HighLowDielectric Constant

1.35 – 1.951.40 - 1.65Refractive index

GlassPolymers


Compensation of CharacteristicsCompensation of CharacteristicsMechanical Properties Silica/PDMS HYBRIMER


Functionality of HYBRIMERFunctionality of HYBRIMERHydrophilic and Hydrophobic Coatings


Optical Application of HYBRIMEROptical Application of HYBRIMERSolid state dye laser materials

Rare-earth emission materials

Nonlinear optical and photorefractive materials

Photochemical hole burning materials

Photochromic materials

Optical sensor matrials

Optical waveguide materials


Functionality of HYBRIMERFunctionality of HYBRIMERNLO Chromophore HYBRIMER

UnpoledPolymers

PoledPolymers

heating around Tgelectric field oncoolingelectric field off

SHG

EO

EOwave length changeFrequancy Doubling

amplitude, wave formE-O Modulators

spatial, wave frontSpatial Light Modulators

(a)

(b)

(c)

••

••

UnpoledSol-GelHybrids

PoledSol-GelHybrids

이광섭 교수, 한남대

HC

l / DM

F-C

H3 O

H

-H2 O

Si(OEt)3(OEt)3Si

NL

O

Si

SiO

O SiO

OO

SiSi

O

O

O

SiOSi

OSi

OO

SiOSi

O OSi

O

Si

O O

Si

Si O

OSi O

O Si

OSi

OSi

O

O O

O

Si

Si

SiO

O O

O O

O

Si

Si

SiO

O SiO

OO

SiSi

O

O

O

SiOSi

OSi

OO

SiOSi

O OSi

O

Si

O O

Si

Si O

OSi O

O Si

OSi

OSi

O

O O

O

Si

Si

SiO

O O

O O

O

Si

NLO

NLO

NLO

NLO

NLO

NLO

NLO

NLO

NL

O

NL

O

NLO

NLO


Silica vs. Polymer for Waveguide MaterialsSilica vs. Polymer for Waveguide Materials

SilicaSilica PolymerPolymerSpin-on

Low temp.Easy, Cheap

Versatile

FHD,CVDHigh temp

Difficult,Expensive.Process

AbsorptionLower Low

Mechanical LowHigh

Thermal LowHigh

Thermo-optics HighLowNot VersatileDesign

FunctionalityNot Versatile

PolarizationdependenceStress Anisotropy


Advantages of HYBRIMER WaveguideAdvantages 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

• Manipulation of refractive indexin 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

HYBRIMER Waveguide

Polymer Waveguide


Micro-Patterning in HYBMRIMER by Photo-polymerization

hν

R'=CH3;C2H4OH = - C3H6OOC -

Photo-initiator

Selective etchingUV

developing

Fabrication of waveguides


Encapsulation & Immobilization in HYBRIMEREncapsulation & Immobilization in HYBRIMEREntrapment of biomolecules and chemical species in porous structureBetter compatibility in organic environmentsApplications in biosensor, bioreactors, chemical sensor, catalysis


VI. Sol-Gel Process of Mesoporous MaterialsMicelle 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

Hexagonal Cubic 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 silicateAlkyltrimethylammonium 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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Documents

solgel science

solgel process of silicaiv

liquid sol

solvent wet gel

solgel transition gelation

sol preparation

pores of wet gel

small solid particles