Physics and Chemistry of Hybrid Organic-Inorganic Materials
Lecture 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
Improvement on either organic or inorganic components
Metal oxide network
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 melting polymer and mixing
Preparation by dissolving polymer and mixing
Particle dispersion in solid polymer
Solid Inorganic particles
Solid Inorganic particles dispersed
in same solvent
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.
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 matrixThe inorganic particles is the dispersed phase or filler
Silica particle (130 nm in diameter)
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 dispersedparticles in polymer
Generally meta-stable: particles will segregate if given the opportunity
POSS in polypropylene
Sedimentation or floatation of particles during mixing and drying
(a) (b)
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.
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
Particles in polymers: thixotropesParticles 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
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
TEOSConcentrations
0.011M (0.03736g) to 0.28M (0.934g)
NH4OHConcentrations0.1M to 1.2M
Hydrolysis: exchange of OEt groups with OH groupsCondensation: 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
Control of particle size by changing the concentration of ammonium hydroxide with
0.28M TEOS
Rayleigh scattering
Light scattering from particle/polymer composites
Other ways to make particles: Synthesis of T8 POSS “particle”
Yields are not always so good
Hybrid monomer
Hydrolysis & condensation
Synthesis of Phenyl T8 POSS
Also works from the polymer!!!!Best way to make POSS
Hydrolysis & condensation
breaking and remaking bonds
Hybrid monomer
“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. 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.
Hydrolysis & condensation
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
POSS physically dispersed in polypropylene
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
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
.
Composites Part B: Engineering Volume 39, Issue 6 2008 933 - 961
Tensile modulus (stiffness) of nylon 6 nanocomposites as a function of SiO2 content
Modulus increases as inorganic content increases
More inorganic: higher modulus
Less inorganic: lower modulus
No inorganic, just nylon: lowest modulus
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
polymer exfoliated clay: No stacking of aluminosilicatesheets
organic polymer intercalated into clay
Process for forming clay polymer composites
clay with Na counterions clay with surfactant
counterions
X-ray diffraction
From Giannelis et al., Adv. Polym. Sci., 118 (1999)
Detecting intercalation and exfoliation
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
Macromolecules, 2006, 39 (16), pp 5194–5205
Nature Materials 9, 868–871 (2010)
High modulusStrongStable
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)
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.