1. Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 6: Polymerizing monomers to make hybrids preassembled inorganic phase (particles, fibers) dispersed in organic phase

2. Key concepts Reasons for making an inorganic filled organic polymer hybrid: improve strength, abrasion resistance, modulus, hardness, inflammability, Metal oxide inorganic particles can be made by sol-gel, Stober preparation, precipitation, flame synthesis Organic phase: organic polymers melted or in solution Inorganic particles increase viscosity in polymer melt or solution Particle aggregation ruins hybrid effects smaller the particle, the greater the strength and modulus of the hybrid the higher the particle concentration, the greater the strength and modulus of the hybrid

3. What are Hybrid Materials? Composite materials mixtures of organic and inorganic components Improvement on either organic or inorganic components Metal oxide network

4. Making Hybrid Materials: Class 1A (pre-formed particles and fibers) Physical mixing of particles in melt or solution Easiest hybrid to make Most common hybrids

5. Preparation by melting polymer and mixing

6. Preparation by dissolving polymer and mixing Particle dispersion in solid polymer Solid Inorganic particles Solid Inorganic particles dispersed in same solvent

7. Reasons for making a particle-filled polymer Fillers (CaCO 3, Silica, Talc, wood powder) are cheaper than some plastics-cut cost. Reduce Coefficient of thermal expansion of polymer Reduce shrinkage during thermoset curing Improve abrasion resistance and hardness Increase modulus Make melt more viscous or gel (thixotrope) Make Flame resistant Aesthetics – pearlesence or opalescence

8. Organic polymers that have been used: Thermoplastics: polystyrene, poly(methyl methacrylate), HDPE, polypropylene, Nylon’s, polycarbonate, polyimides, poly(ethylene oxide), polyurethanes, polyesters…. Elastomers: silicones, polyisoprene,… Thermosets: epoxies, Polyelectrolytes: Nafion practically every commercial polymer known.

9. 5 weight percent silica in Nafion Physically mixed hybrids are a composite material based on an inorganic particle & an organic polymer Polymer is the continuous phase or matrix The inorganic particles is the dispersed phase or filler Silica particle (130 nm in diameter)

10. Examples of Physically Mixed Hybrids Paint – poly(vinyl acetate) + TiO 2 Pearlescent paint – polyacrylate + TiO 2 coated mica Make-up or cosmetics – polyvinylpyrrolidone + metal oxides (for color) Sunscreens – polyvinylpyrrolidone or polyethers and TiO 2 or ZnO nanoparticles in water or glycerin

11. Class 1 Hybrids: No covalent bonds between organic & inorganic phases Physically dispersed particles in polymer Generally meta-stable: particles will segregate if given the opportunity POSS in polypropylene

12. Sedimentation or floatation of particles during mixing and drying (a) (b)

13. Sedimentation of particles during mixing and drying (a) (b) Solution viscosity was too low Particles floated to the top of the membrane as the solvent dried Solved problem by evaporating solvent while mixing until viscosity was 65 cP.

14. Influence of nanoparticles on melt viscosity “Nanofillers in polymeric matrix: a study on silica reinforced PA6,” E. Reynaud, Polymer 2001, 42, 8759 Smaller the size particle, the greater the viscosity

15. Particles in polymers: thixotropes Particles are used to stop liquids from flowing until subject to shear. Used in “non-running” or “no-drip” liquid adhesives, paints, and lubricants. Silicone sealant with silica Silicone sealant with NO silica

16. How to make inorganic particles Sol-gel “wet” synthesis Emulsion polymerizations (sol-gel in oil & water) microns in diameter Aerosols/flame syntheses (will not make silsesquioxanes)

17. Sol-gel: Stober synthesis TEOS Concentrations 0.011M (0.03736g) to 0.28M (0.934g) NH 4 OH Concentrations 0.1M to 1.2M Hydrolysis: exchange of OEt groups with OH groups Condensation: Reaction of OH groups to form Si-O-Si links J. Colloid Interface Sci., 26 (1968), pp. 62–69 All particles round and same size

18. Control of particle size by changing the concentration of ammonium hydroxide with 0.28M TEOS Rayleigh scattering

19. Light scattering from particle/polymer composites

20. Other ways to make particles: Synthesis of T8 POSS “particle” Yields are not always so good Hybrid monomer Hydrolysis & condensation

21. Synthesis of Phenyl T8 POSS Also works from the polymer!!!! Best way to make POSS Hydrolysis & condensation breaking and remaking bonds Hybrid monomer

22. “Two-step” method to prepare silsesquioxane particles from hybrid monomers A. Matsuda et al. J. Ceram. Soc. Jap. 2007, 115, 131-135. Typical recipe: 1) PhSi(OEt) 3 (2.4 grams) in 12 mL anethol is mixed with aq. HCl (0.0027 M, 3.6 mL) for 7 h. 2) This sol was added to aq. NH 3 (1M, 32.4 mL) and stirred for 20 h. 3) Particles isolated and washed with centrifugation. Loy, D. A. Macromole Mater Eng. 2012, in press. Hydrolysis & condensation

23. Flame synthesis of inorganic particles Langmuir 2004, 20, 5933

24. Other inorganic fillers include Clays (2-D aluminosilicates)* Fullerene, nanotubes, and graphene* other aluminosilicates Main group metal oxides Transition metal oxide particles Alkali earth carbonates and sulfates Quantum dots Metals *included in this lecture

25. POSS physically dispersed in polypropylene

26. How do you characterize a hybrid: Particle is crystalline Can see if crystals exist in hybrid Macromolecules, 2006, 39 (5), pp 1839–1849 XRD of POSS XRD of POSS in HDPE

27. Influence of nanoparticles on melt viscosity “Nanofillers in polymeric matrix: a study on silica reinforced PA6,” E. Reynaud, Polymer 2001, 42, 8759 Micrographs of the PA-05-S composite (left) and the PA-05-L system (right) (MET) Silica particles mixed into Nylon while melted Viscosity is higher with smaller particles and with more particles

28. . Composites Part B: Engineering Volume 39, Issue 6 2008 933 - 961 Tensile modulus (stiffness) of nylon 6 nanocomposites as a function of SiO 2 content Modulus increases as inorganic content increases More inorganic: higher modulus Less inorganic: lower modulus No inorganic, just nylon: lowest modulus

29. Tensile strength of nylon 6 nanocomposites as a function of SiO 2 content & surface modification using coupling agent With surface modification Without surface modification If surface tensions at surface are too different, poor wetting results in weaker materials. Modify surface to match surface tension – increase in strength.

30. Polymer-clay composites montmorillonite Exfoliated montmorillonite clay 2-Dimensional inorganic phases provide incredible reinforcement

31. Polymer-clay composites Clay: 2-D sheets of alumino-silicate with metal cations in between Replace metal cations with cationic surfactants Replace surfactants with polymers (melted or in solution)-intercalation Heat and apply shear – exfoliation Stronger, fire resistant, less permeable

32. polymer exfoliated clay: No stacking of aluminosilicate sheets organic polymer intercalated into clay Process for forming clay polymer composites clay with Na counterions clay with surfactant counterions

33. X-ray diffraction From Giannelis et al., Adv. Polym. Sci., 118 (1999) Detecting intercalation and exfoliation

34. Tensile strength of non-covalently integrated clay-polystyrene-co-acrylate nanocomposites Mechanics of Composite Materials 2006, 42, 45. +

36. Carbon Spheres (Buckyballs) & Nanotubes & graphene as inorganic fillers Macromolecules, 2006, 39 (16), pp 5194–5205 Nature Materials 9, 868–871 (2010) High modulus Strong Stable

37. Fullerenes as inorganic particles in polymers J. Mater. Chem., 1997,7, 1097-1109 The curves of uniaxial deformation of the LDPE films with different fullerene content: 0 (1), 1 (2), 3 (3), 5 (4) and 10 wt% (5)

38. Summary: Physical mixing of inorganic in organic polymer Made by solvent or melt mixing Particle aggregation will ruin any positive influence from the inorganic particles Nature of non-bonding interactions will affect strength & modulus trends But generally, modulus and strength increases with decreasing particle size Modulus and strength increases with increasing weight percent particle Clay –polymer composites best properties of hybrids so far

39. Study Guide Name Naturally occurring hybrids and describe what they are made of: Nacre (argonite and protein), bone (apatite and protein), enamel (apatite and proteins), dentin (apatite and proteins), echinoderm spines (calcium carbonate and proteins), lobster chitin (Mg, Ca, proteins, carbohydrate), spider fangs(Mn, Zn, proteins, carbohydrate), phytoliths (silica- carbohydrate), sponges (silica-protein). Hierarchical material – different structures at different length scales Physical mixing of hybrids: in melted polymer or adding dispersed particles to polymer solution then evaporating solvent Clay polymer composites are made by intercalation and exfoliation Common inorganic particles – carbon black, silica, titanium dioxide, clay, calcium carbonate, fullerenes and carbon nanotubes What are nanocomposites- A nanocomposite is a two phase hybrid with one or both phases having structural dimensions in the 1-100 nanometer length scale. Paint, glue, and cosmetics are examples.