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
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 melting polymer and mixing
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
POSS in polypropylene
Generally meta-stable: particles will segregate
if given the opportunity
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
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
Light scattering from
particle/polymer composites
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
Hybrid
monomer
Hydrolysis &
condensation
breaking and
remaking bonds
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.
Loy, D. A. Macromole Mater Eng. 2012, in press.
3) Particles isolated and washed with
centrifugation.
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
POSS physically dispersed in polypropylene
How do you
characterize a
hybrid:
XRD of POSS
Particle is
crystalline
Can see if
crystals exist in
hybrid
Macromolecules, 2006, 39 (5), pp 1839–1849
XRD of POSS in HDPE
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 (silicacarbohydrate), 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.