Key points on how to characterize the structure of a hybrid material

1. Physics and Chemistry of Hybrid Organic-Inorganic MaterialsLecture 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)

3. Hybrid Materials Synthesis & Processing Materials Science is a key field in studying hybrids Properties Structure 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

5. Describe the material below

6. Describe the material below

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

8. Types of Polymers & solubility soluble insoluble If swelling of polymer in solvent is observed: low low of crosslinking No swelling, then highly crosslinked.

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

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.

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 Run experiment Work-up data

12. Epoxide Open Epoxide Closed A) B) C) Epoxide Open Epoxide Closed 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 13C NMR

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= C=O H2C= 200 180 160 140 120 100 80 60 40 20 ppm β α γ 200 180 160 140 120 100 80 60 40 20 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.

15. Infrared spectrum of T8 Phenyl silsesquioxane

16. 1790-1720 very strong no yes 1610 –1590, 1600 – 1580 and 1510 - 1490 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 3500 - 3200 1680 - 1630 strong 1450 -1410 sharp strong 1450 - 1410 sharp 1550 - 1530 1100 - 1000 Polyvinyl acetate, PVC-copolymers Modif. Epoxies Polycarbon- ates Phenol derivatives, Epoxies Cellophan, Alkylcellulose, PVA, PEO Polyamides, amines Alkylsilicone, aliphatic hy drocarbons, Polytetra fluorethylene Thiokol Acrylics, Polyester Cellulose ester Polyurethane Alkyd-, Polyesters, Cellulose ether, PVC(plasticized) Polystyrenes, Arylsilicones, Aryl-alkyl Silicone Copolymers PAN, PVC, Polyvinylidene chloride POM Nitrocellulose cellophane Identification of organic polymers using Infrared spectroscopy

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)

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.

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?

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)

21. AFM of polyethylene crystallite microcrystals Inorganic crystals 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)

23. XRD of crystalline material 2 theta plot BCC iron

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

25. 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!!!!!!!!!

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

27. Amorphous materials: XRD amorphous amorphous crystalline

28. XRD of organic polymers amorphous semi-crystalline crystalline

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

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

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

32. Electron Microscopy • Scanning electron microscopy (reflection) • Transmission electron microscopy (through sample) TEM of surfactant templated silsesquioxane TEM of amorphous hybrid 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.

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

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

36. Differential Scanning Calorimetry 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.

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.

39. Literature procedure: See how experimentals are written in good papers. Use them as model

40. Template for lab notebook:

41. Template for research labnotebook: