Physics and Chemistry of Hybrid Organic-Inorganic MaterialsLecture 6: Polymerizing monomers to make hybrids preassembled inorganic phase (particles, fibers) dispersed in organic phase
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
What are Hybrid Materials? Composite materials mixtures of organic and inorganic components Metal oxide network Improvement on either organic or inorganic components
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
Preparation by dissolving polymer and mixing Solid Inorganic particles Solid Inorganic particles dispersed in same solvent Particle dispersion in solid polymer
Reasons for making a particle-filled polymer • Fillers (CaCO3, 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
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.
Physically mixed hybrids are a composite material based on an inorganic particle & an organic polymer Silica particle (130 nm in diameter) 5 weight percent silica in Nafion Polymer is the continuous phase or matrix The inorganic particles is the dispersed phase or filler
Examples of Physically Mixed Hybrids • Paint – poly(vinyl acetate) + TiO2 • Pearlescent paint – polyacrylate + TiO2 coated mica • Make-up or cosmetics – polyvinylpyrrolidone + metal oxides (for color) • Sunscreens – polyvinylpyrrolidone or polyethers and TiO2 or ZnO nanoparticles in water or glycerin
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
Sedimentation or floatation of particles during mixing and drying (b) (a)
Sedimentation of particles during mixing and drying (b) (a) • 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.
Influence of nanoparticles on melt viscosity Smaller the size particle, the greater the viscosity “Nanofillers in polymeric matrix: a study on silica reinforced PA6,” E. Reynaud, Polymer 2001, 42, 8759
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 NO silica Silicone sealant with silica
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)
Sol-gel: Stober synthesis All particles round and same size TEOS Concentrations 0.011M (0.03736g) to 0.28M (0.934g) NH4OH 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
Control of particle size by changing the concentration of ammonium hydroxide with 0.28M TEOS Rayleigh scattering
Other ways to make particles: Synthesis of T8 POSS “particle” Hybrid monomer Hydrolysis & condensation Yields are not always so good
Synthesis of Phenyl T8 POSS Hydrolysis & condensation breaking and remaking bonds Hybrid monomer Also works from the polymer!!!! Best way to make POSS
“Two-step” method to prepare silsesquioxane particles from hybrid monomers Hydrolysis & condensation 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. NH3 (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. A. Matsuda et al. J. Ceram. Soc. Jap. 2007, 115, 131-135.
Flame synthesis of inorganic particles Langmuir 2004, 20, 5933
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
How do you characterize a hybrid: Particle is crystalline Can see if crystals exist in hybrid XRD of POSS XRD of POSS in HDPE Macromolecules, 2006, 39 (5), pp 1839–1849
Influence of nanoparticles on melt viscosity 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 “Nanofillers in polymeric matrix: a study on silica reinforced PA6,” E. Reynaud, Polymer 2001, 42, 8759
Tensile modulus (stiffness) of nylon 6 nanocomposites as a function of SiO2 content More inorganic: higher modulus Less inorganic: lower modulus No inorganic, just nylon: lowest modulus . Modulus increases as inorganic content increases Composites Part B: Engineering Volume 39, Issue 6 2008 933 - 961
Tensile strength of nylon 6 nanocomposites as a function of SiO2 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.
Polymer-clay composites montmorillonite Exfoliated montmorillonite clay 2-Dimensional inorganic phases provide incredible reinforcement
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
Process for forming clay polymer composites clay with Na counterions clay with surfactant counterions organic polymer intercalated into clay polymer exfoliated clay: No stacking of aluminosilicate sheets
Detecting intercalation and exfoliation X-ray diffraction From Giannelis et al., Adv. Polym. Sci., 118 (1999)
Tensile strength of non-covalently integrated clay-polystyrene-co-acrylate nanocomposites + Mechanics of Composite Materials 2006, 42, 45.
Carbon Spheres (Buckyballs) & Nanotubes & graphene as inorganic fillers High modulus Strong Stable Macromolecules, 2006, 39 (16), pp 5194–5205 Nature Materials 9, 868–871 (2010)
Fullerenes as inorganic particles in polymers 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) J. Mater. Chem., 1997,7, 1097-1109
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
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.