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.