Transcript Physics and Chemistry of Hybrid Organic

Physics and Chemistry of Hybrid
Organic-Inorganic Materials
Lecture 2: Characterizing the
structure of Hybrids
Key points on how to characterize the
structure of a hybrid material
• appearance of the material
• solubility in organic solvents and water
• Amorphous versus crystalline materials
– X-ray diffraction, calorimetry, dilatometry, SEM, TEM and
AFM
• Composition: Elemental analysis, x-ray techniques
• Molecular level structure: X-ray (if crystalline), NMR, infrared or
Raman spectroscopies.
• Morphology: TEM, SEM, AFM, confocal fluorescence microscopy,
optical microscopy
• Fractal structures: small angle scattering (neutron or X-ray)
• If soluble, molecular weight (Gel Permeation Chromatography,
Vapor Phase Osmometry, Dynamic light scattering)
Hybrid Materials
Materials
Science is a
key field in
studying
hybrids
Synthesis
&
Processing
Properties
Structure
Function,
Application,
Performanc
e
First step in characterizing a hybrid:
• Use your senses (take pictures to document)
– What color? Does it fluoresce
– Transparent or opaque?
– Homogeneous in appearance?
– Solid or liquid
– Tacky or sticky or brittle or tough
• Mass – compare with theoretical yield
Describe the material below
Describe the material below
Second, try and dissolve the hybrid
in different solvents
• 50 milligrams of material in glass vial with 20 mL of:
water, ethanol, benzene, methylene chloride,
tetrahydrofuran, acetonitrile, hexane, acetone,
diethyl ether, dimethyl sulfoxide, N-methyl
pyrrolidone (NMP)
• Leave samples in solvents at room temp overnight.
Look for swelling if not dissolved.
• Next, try boiling polymer in solvent for 4 hours.
• If it doesn’t dissolve its probably cross-linked or
really crystalline
Types of Polymers & solubility
X
n
soluble
n-2
X
Functionality of Two
Linear Polymer: soluble, elastic
insoluble
If swelling of polymer
in solvent is
observed: low low of
crosslinking
X
X
X
Functionality of 3
No swelling, then
highly crosslinked.
crosslinked, brittle material
gel or precipitate
Structural Characterization of
soluble polymers
• 1H & 13C & 29Si Nuclear Magnetic Resonance
and infrared spectroscopy
• Molecular weight by gel permeation
chromatography, dynamic light scattering,
viscosity or vapor phase osomometry
• Composition by combustion analyses
• X-ray diffraction on film or powder
• Viscosity of dilute solutions- shape of polymer
Nuclear Magnetic Resonance
(NMR) Spectroscopy
• Probably the most powerful and general
technique for structural characterization
• Uses radio frequency photon absorption to
change nuclear spin states in 1H, 13C and 29Si
atoms in molecules or materials
• Most commonly used with samples in solution
• Can also be used with insoluble solids
• Signal chemical shift and coupling are used to
determine structures.
Structure determination of organic
compounds using NMR:
1)
2)
3)
4)
5)
Types of protons & carbons present
Numbers of protons on each carbon
Number of protons on adjacent carbons
Stereochemistry of adjacent protons
Some longer distance information
Dissolve sample
in deuterated solvent
Place solution in
glass NMR tube
Run experiment
Work-up data
Solution Nuclear Magnetic
Resonance spectroscopy
• Key tool in indentifying soluble polymers or figuring
out their structure.
• 1H, 13C and 29Si nuclei have spins of 1/2
Epoxide Open
A)
Epoxide Open
B)
C)
Epoxide
Closed
Epoxide Closed
13C
NMR
Solid state NMR
Excellent tool for characterizing insoluble hybrids
Best with 13C and 29Si, not so good with 1H
β
γ
C=O
H3C
α
C=
H2C=
200 180 160 140 120 100
80
60
40
β
γ
200 180 160 140 120 100
80
20 ppm
60
40
α
20 ppm
Broader peaks than solution. More sample is required.
Infrared Spectroscopy
• Structural information based on bond
vibrational absorptions in the infrared
wavelengths.
• Harder to determine structure than with NMR
• Excellent for corroborating other
characterization techniques.
Infrared spectrum of T8 Phenyl
silsesquioxane
Identification of organic polymers using Infrared spectroscopy
1790-1720
yes
1610-1590,
1600-1580 and
1510-1490
very
strong
no
1610 –1590,
1600 – 1580 and
1510 - 1490
All numbers have the meaning of
wave numbers
and are given in cm-1
3500 3200
840 - 820 strong
Modif.
Epoxies
Polycarbonates
Alkyd-,
Polyesters,
Cellulose ether,
PVC(plasticized)
1450 - 1410 sharp
Polyvinyl
acetate,
PVCcopolymers
3500 - 3200
1680 - 1630
Cellulose
ester
Polyurethane
1450 -1410 sharp
1550 - 1530
1100 - 1000
Phenol
derivatives,
Epoxies
Acrylics,
Polyester
strong
Polyamides
,
amines
Polystyrenes,
Arylsilicones,
Aryl-alkyl Silicone
Copolymers
Nitrocellulose
cellophane
Cellophan,
Alkylcellulose,
PVA, PEO
PAN, PVC,
Polyvinyliden
e
chloride
POM
Alkylsilicone,
aliphatic hy
drocarbons,
Polytetra
fluorethylene
Thiokol
Molecular Weight determinations
• Only on soluble polymers
• Different methods:
– Gel permeation chromatography (MN,
MW)
– Dynamic Light scattering (MN, MW)
– Viscosity (MV)
– Vapor phase osmometry (MN)
Composition: What elements are
present and in what percent
• Organics are analyzed by combustion analysis
• Inorganics may be analyzed by
– emission or absorption spectroscopies
– X-ray fluorescence
– Elemental dispersive spectroscopy
• The amount of inorganic in a hybrid can be
determined gravimetrically by burning away
all of the organic.
Amorphous versus crystalline
• Amorphous – kinetic, no long range order, no
time for crystals to grow from solution or
liquid.
How can you tell if a material is amorphous?
• Crytsalline: thermdynamic structures made
with reversiblity to remove defects and
correct growth. Long range order.
How can you tell if a material is crystalline?
Crystalline materials
• Long range order: Bragg diffraction of
electromagnetic radiation (or electron beams
in TEM) by crystalline lattice into sharp peaks.
• Solid structures with geometric shapes,
straight lines and flat surfaces, and vertices.
• Optical affects like bifringence
• Direct visuallization of crystal at molecular
level with AFM or STEM.
• Melting point (not always though)
AFM of
polyethylene
crystallite
microcrystals
Inorganic crystals
XRD from semicrystalline
polymer film
Rutile titania crystals
in amorphous TiO2
Micrograph of polymer
crystalline spherulites
XRD (wide angle)
• Single crystal or microcrystalline powder
(crystals with atomic or molecular scale order)


2
dsin

hk l
XRD of crystalline material
2 theta plot
BCC iron
Amorphous materials
• No long range order: diffuse peaks may be
present, due to average heavy atom distances.
• No crystalline geometries, glass like fractures
(conchoidal)
• Aggregate spherical particles common
• Negative evidence for crystal at molecular
level with AFM or STEM.
• No Melting point
X-ray powder diffraction from
polybenzylsilsesquioxane “LADDER” Polymer
4.2 A
3.1 A
Mostly amorphous material.
Small sharp peaks are due to contaminant from preparation
Not a ladder polymer!!!!!!!!!
XRD amorphous material
Al2O3 thin films prepared by spray pyrolysis
J. Phys.: Condens. Matter 13 No 50 (17
December 2001) L955-L959
Amorphous materials: XRD
amorphous
amorphous
crystalline
XRD of organic
polymers
amorphous
semi-crystalline
crystalline
Conchoidal Fractures in
amorphous materials
Crystals break along miller planes
Unless microcrystalline
If crystals are small compared to
impact, conchoidal fracture can
occur
In sandstone 3 meters tall)
In metal
Or third, Structural Characterization
of insoluble polymers
• Harder to characterize
• Does it burn (many inorganics do not)
• Solid state 1H & 13C & 29Si Nuclear Magnetic
Resonance and infrared spectroscopy
• X-ray diffraction on film or powder
• Composition by
– combustion analyses if organic
– X-ray fluorescence if inorganic
Electron Microscopy
• Scanning electron microscopy (reflection)
• Transmission electron microscopy (through sample)
TEM of surfactant
templated
silsesquioxane
SEM of
surfactant
templated
hybrid
TEM of
amorphous
hybrid
SEM of
amorphous
hybrid
Surface area measurements
• Gas sorption porosimetry at the boiling point
of the analysis gas (nitrogen).
• Meassuring cell pressure after adsorption of
gas in small doses on an evacuated sample of
known mass generates a gas sorption
isotherm.
• Then you determine surface area, pore size,
pore volume, pore size distribution from
isotherm using mathematical models.
Morphological Characterization of
polymers
• If opaque or transluscent, SEM and optical
microscopy (bifringence)-crystalline or
amorphous & more.
• Fracture polymer and look at fracture surfaces
• Look for phase separation (like immiscible
block copolymers)
• Look for long range order
• Look for pores
Morphology of hybrids
TEM, SEM and AFM
are good tools for
evaluating
morphology
One
continuous
phase
(light); One
planar
dispersed
phase
(black)
solid (1) phase
of particles with
pores. Other
phase is gas.
Long range
order, no
particulate
structure.
Two phases
Differential Scanning Calorimetry
Glass transition temperatures, melting points and reactions
Not every polymer needs all of these
analyses, but structure is the most
basic and important
• Known (described in literature) polymers
need less structural characterization. Often
just IR and Mw from GPC.
• New polymers need complete structural
characterization: NMR, IR, Combustion
analysis, GPC, solubility, glass transition temp
and/or melting point.
Summation
• Characterization is key step in any science
with hybrid materials
• NMR, XRD, IR are central tools for
characterization
• Composition – including fraction inorganic to
organic is also needed.
• Determination if the material is ordered or not
• Microscopic evaluation of morphology aids in
identifying phase separated systems.
Literature procedure:
See how experimentals are written in good papers. Use them as model
Template for lab notebook:
Template for research labnotebook: