Hybrid Materials & POSS
Lecture 5: : Class 1A preassembled inorganic phase
(particles, fibers) dispersed in organic phase
Class 1A 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
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.
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
Just as the colloid made from blending oil and water
will return back to two continuous phases
With time
Which is the lower energy state?
Aggregation of particles in polymer
•
•
•
Silica in polydimethylsiloxane (PDMS).
Silica and PDMS in toluene were mixed, then cast and
dried.
Aggregation occurs during drying stage before
viscosity gets too high.
Polymer 205, 46, 41270
Sedimentation 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.
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)
• 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
Reaction Scale = 15mL and 60mL
TEOS distilled
NH4OH titrated ( 9M)
Anhydrous ethanol
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”
Yields are not always so good
Synthesis of Phenyl T8 POSS
Also works from the polymer!!!!
Best way to make POSS
“Two-step” method to prepare
silsesquioxane particles
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
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
“Nanofillers in polymeric matrix: a study on silica reinforced PA6,” E. Reynaud, Polymer 2001, 42, 8759
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
Tensile modulus (stiffness) of nylon 6 nanocomposites as a function of SiO2 content
.
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
Summary for Class 1: particles 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
Polymer-clay composites (Class 1A)
montmorillonite
Exfoliated montmorillonite clay
Polymer-clay composites (Class 1A)
• 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
intercalated
exfloliated
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
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
• Class 1A materials rely on non-bonding
interactions and so it can be difficult finding
optimum conditions to match the surfaces of
filler and polymer to give good interactions.
• Spherical particles are not as good as linear or
2-D fillers in improving mechanical strength.
Next we look at in-situ formation of particles
where we add the precursor to the polymer
and the particle forms in place.