1. Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 2: Characterizing the structure of Hybrids

2. 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)
These key points are the things you wish to focus on for mastering this lecture material.

3. Synthesis & Processing
Hybrid Materials
Synthesis & Processing
Materials Science is a key field in studying hybrids
Properties
Structure
In this section we will be looking at the basic structural principles involved in hybrid materials.
Function, Application,
Performance

4. 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
Most research papers provide inadequate descriptions to the reader of what happened during a reaction and what the sample looked like. Use your senses.

5. Describe the material below
Material is transparent, colorless, exhibits glass like fractures. If you were holding it you would be able to describe whether it was soft or hard, rubbery or brittle, if there was any sign of liquid, or coolness, approximate density (heavy or light).

6. Describe the material below
Thin sections appear transparent, but a great deal of scattering of light and some absorption of light are observed. Light brown or tea tint to the block. No crystalline habits or planar structures indicative of crystals.

7. 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
Any time you make a polymer one of the first things you do is see what solvents it dissolves in (with heating). This can be done with a 100 milligrams of material. It is actually a good idea to weigh out the polymer so you can gauge if it is very soluble, slightly soluble or only swells or do swelling at all. Pay attention to if the solvent even wets the polymer.

8. Types of Polymers & solubility
soluble
insoluble
If swelling of polymer in solvent is observed: low low of crosslinking
No swelling, then highly crosslinked.
This shows you the linear architectures that are generally soluble in some solvent unless very crystalline. This class would include the polymers physically mixed but not chemically reacted with an inorganic filler. And the cross-linked polymer architectures (such as epoxies or silica or many hybrids) that will not dissolve. This class includes most of the hybrids. This means that generally hybirds are not soluble. If they are, they cannot be crossslinked.

9. 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
Now remember if you are remaking a known polymer, you don’t need to do as much. A carbon NMR or IR to confirm identity and molecular weight is critical for a known, previously reported polymer. If the polymer was incompletely described in the literature then do more characterization to fill the gap. Once you know a new polymer is soluble, the slide here tells you what you should do to characterize it. Now, you aren’t required to have x-ray diffraction or viscosity but its prudent. Viscosity is powerful because the Mark exponent tells you something about the shape of the polymer in solution.

10. 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.
NMR background info.

11. Structure determination of organic compounds using NMR:
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
Ease of running NMR
Run experiment
Work-up data

12. 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
Epoxide Closed
Epoxide
Closed A) B) C)
13C NMR
Exam of using C-13 NMR to characterize an hybrid with an epoxy group.

13. Solid state NMR Excellent tool for characterizing insoluble hybrids
Best with 13C and 29Si, not so good with 1H β γ
H3C α
C=O C=
H2C=
ppm β γ α
An example of using C-13 solid state NMR to characterize two insoluble hybrids made in my lab from the same monomer using two different reaction conditions.
ppm
Broader peaks than solution. More sample is required.

14. 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.
Intor to IR spectroscopy

15. Infrared spectrum of T8 Phenyl silsesquioxane
AN typical IR spectrum in transmission mode.

16. All numbers have the meaning of wave numbers
Identification of organic polymers using Infrared spectroscopy
very strong ,
and
Modif.
Epoxies
Polycarbon-
ates
Alkyd-,
Polyesters,
Cellulose ether,
PVC(plasticized)
Polyvinyl
acetate,
PVC-copolymers
Cellulose
ester
Polyurethane
Acrylics,
Polyester
Phenol
derivatives,
Polystyrenes,
Arylsilicones,
Aryl-alkyl Silicone Copolymers
Polyamides,
amines
Nitrocellulose
cellophane
Cellophan,
Alkylcellulose,
PVA, PEO
PAN, PVC,
Polyvinylidene
chloride
POM
Alkylsilicone,
aliphatic hy
drocarbons,
Polytetra
fluorethylene
Thiokol
sharp
strong
1610 –1590,
1600 – 1580 and
All numbers have the meaning of wave numbers
and are given in cm-1
yes no
A very useful chart to identifying common polymer types based on their IR.

17. 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)
If you have made an organic polymer that is soluble, it is standard to determine the molecular weight. The easiest and cheapest method is by viscosity. The best method is by gel permeation chromatography

18. 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.
Elemental composition methods.

19. 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?
Any time you make a material you should determine if the material is amorphous or crystalline.

20. 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)
key characteristics of crystalline materials.

21. AFM of polyethylene crystallite
microcrystals
Inorganic crystals
Some images of crystalline materials using techniques that would help prove crystallinity.
XRD from semicrystalline
polymer film
Rutile titania crystals in amorphous TiO2
Micrograph of polymer crystalline spherulites

22. XRD (wide angle)
Single crystal or microcrystalline powder (crystals with atomic or molecular scale order)
Basic XRD

23. XRD of crystalline material
2 theta plot
BCC iron
crystalline iron diffraction

24. 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
Characterisitics of amorphous materials.

25. X-ray powder diffraction from polybenzylsilsesquioxane “LADDER” Polymer
Example of an amorphous material (the big fat peak) and a crystalline contaminant (the little sharp peaks).
Mostly amorphous material.
Small sharp peaks are due to contaminant from preparation
Not a ladder polymer!!!!!!!!!

26. XRD amorphous material
Amorphous alumina – no sharp peaks.
Al2O3 thin films prepared by spray pyrolysis
J. Phys.: Condens. Matter 13 No 50 (17 December 2001) L955-L959

27. Amorphous materials: XRD
Some more examples of amorphous samples (silica and A4) and a crystalline alumina.
crystalline

28. XRD of organic polymers
amorphous
semi-crystalline
A single type of polymer in amorphous, semicrystalline (means mixture of crystalline and amorphous) and highly crystalline samples.
crystalline

29. Conchoidal Fractures in amorphous materials
Signature for amorphous materials
Crystals break along miller planes
Unless microcrystalline

30. If crystals are small compared to impact, conchoidal fracture can occur
Signature for amorphous materials
In sandstone 3 meters tall)
In metal

31. 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
If the polymer is insoluble and amorphous, characterization used to be pretty hard. Its still harder than for a soluble polymer. Most places have access to a solid state NMR now days. Before the 1980’s, that was not the case and many insoluble amorphous materials were neglected because their structure was not determined. Remember you have to prove a structure. Just because you want to have a certain structure doesn’t mean that you have it. The burden of proof is on you.

32. Electron Microscopy Scanning electron microscopy (reflection)
Transmission electron microscopy (through sample)
TEM of surfactant templated silsesquioxane
TEM of amorphous hybrid
Electron microscopy can provide information on morphology and also surface area and pore sizes.
SEM of amorphous hybrid
SEM of surfactant templated
hybrid

33. 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.
Extremely valuable technique widely used in petroleum and geological engineering, materials science, pharmaceutical fields

34. 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
Once you have characterized the structure of a material, you still need to look at longer length scale structures. Nano- to Microscopic structures are called morphology and these are characerized using AFM, SEM, TEM, and confocal fluorescence microscopy.

35. Morphology of hybrids
TEM, SEM and AFM are good tools for evaluating morphology
solid (1) phase of particles with pores. Other phase is gas.
One continuous phase (light); One planar dispersed phase (black)
Long range order, no particulate structure.
Two phases
Here are some examples of micrographs showing different hybrid morphologies.

36. Differential Scanning Calorimetry
This is an example of some of the information you can get from a DSC. Note that it can tell you if something is crystalline (confirm with x-ray).
Glass transition temperatures, melting points and reactions

37. 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.
Again even known polymers should be checked for identity and molecular weight.

38. 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.
sumation

39. Literature procedure:
With that in mind, here is an experimentals from a research paper that describes a minimal characterization of a hybrid material. This was done in the late 1980’s and many solid state techniques you have access to were not available. I ran the solid state NMR at a regional NMR facility in Colorado-about 2000 kilometers away from where I was studying.
See how experimentals are written in good papers. Use them as model

40. Template for lab notebook:
This is a template I give my research group to help them remember what they need to do for characterization of a monomer or small molecule.

41. Template for research labnotebook:
This is a template I give my research group to help them remember what they need to do for characterization of a soluble polymer.

42. This is a template I give my research group to help them remember what they need to do for characterization of an insoluble polymer.