alex van herk, hans heuts, martin jung, syed imran ali...
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Multicompartment latex particles design based on possible biomedical and coatings applications
Alex van Herk, Hans Heuts,
Martin Jung, Syed Imran Ali, Dirk-Jan Voorn,
Marshall Ming, Jens Hartig
Emulsion Polymerization Research Group
Eindhoven University of Technology
Berlin July 12 2009
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Molecules Particles
Polymer Colloids
SuprastructuresFunctionalities
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Polymer Colloids = Latex particles are nanosized
polymer particles, colloidally stabilized (usually) in water.
Main production methods: -Emulsion polymerization
-Miniemulsion polymerization (77)
Main applications: -Water-borne Coatings (paper/architectural/car)
-Water-borne Adhesives
100nm1nm
100nm1nm
Polymer Colloids
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Emulsion polymerization
Miniemulsion polymerization
Microemulsion polymerization
Suspension polymerization
μm
nm
μm
nm
nm
Production techniques
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6addapted from Mohwald Internet source
Encapsulation in aqueous media
Molecules Particles
LBL Driving force: Charges/Other Emulsion polymerization
Driving force: Water Insolubility
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Release of drugs, crosslinking agents, anti-
corrosive agents etc.
Time Time
Concen
tration
Pulse Pulse
Continuous release,
often based on
(bio)degradation of
polymer.
Pulsatile response,
based on external
trigger pulse, e.g.
pH, Ultrasound,
heat. Release per
pulse not constant.
Time
Pulsatile response,
based on external
trigger pulse, e.g.
pH, Ultrasound,
heat. Release per
pulse constant.
Pulse Pulse
Controlled Release Profiles
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Targeting in the human body
• Targeting particles to enter certain organs in the human body depends on particle size. For example targeting nanoparticles preferable to brain tissue requires particles of 100 nm
• For example, other organs need particles of 50-70 nm
• Preferably narrow particle size distributions because release and degradation will depend on particle size
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Influence of particle size
• Implant too big, molecules on the outside of the
implant will quickly release, molecules on the
inside much slower. It is expected that reducing
particle size will lead to more uniform release
per pulse. Bigger molecules need smaller
particles to be able to diffuse out Ddif
• For targeting also a specific particle size is
needed Dtar Ddif ≠ Dtar
Dtar
Ddif
Multicompartment nanoparticle where
all compartments are the same; Pimple
particle
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Nanobottles
Pulsatile release of substances by a 2
compartment particle where one part is the container
and the other part (the lid) is controlling diffusion out of
the container through external triggering; nanobottle
2-compartment nanoparticle;
Nanobottle
4-compartment nanoparticle;
Vinegar-oil nanobottle
Janus particle
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Vesicles as a route towards multicompartment
nanoparticles
swell bilayer
with monomer polymerize
Jung et al. Langmuir 1997, 13, 6877; Langmuir 2000, 16, 968.
Nanobottles
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application of polymerisable amphiphiles
+ crosslinking amphiphiles
+ styrene
100 nm 100 nm
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Influence of initiator.
The “matrioshka” architecture
On the way towards Vinegar-oil nanoparticlesthermal polymerisation at 60°C, V50
100 nm
N NNH
H3N
HN
NH3
ClCl
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Styrene
Vesicle Polymerization…
Some new morphologies.
Nanobottles Pimple particles Pimple particles
Butyl acrylate Butyl methacrylate
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Hybrid multicompartment nanoparticles
Clay/Polymer nanocomposites• Recently clay platelets have been introduced as
nanocontainers for the release of, for example, anticorrosive
agents in paints;M.l. Zheludkevich et al. University of Aveiro, Portugal, CoSi Conference 23-27 june
2008
• Clay platelets can also be regarded as morphology modifiers
• Clay platelets can improve barrier properties of coatings
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Why anisotropic composite latex particles?
• Clay encapsulated spherical latex particles can improve material properties
by giving maximum exfoliation and minimum aggregation
Flat
particles
Spherical
particles
• Anisotropic (preferably flat) latex particles can induce anisotropy into the
final film and this would significantly improve the final properties
• For example, barrier properties might be expected to improve because clay
platelets align parallel to the substrate during film formation
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Challenges in Clay encapsulation
through emulsion polymerization
Armoured
latex
particles
Secondary
nucleation
Stacking
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Procedures for clay encapsulation by emulsion
polymerization
Edge modification
Face modification
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Modifications of clay
Face modification through PEO-V+ cation exchange
• PEO-V+ readily exchange with the Na+ stabilizing molecules
Covalent edge modification
• Titanate and siloxane modification of clay by
reaction with OH groups is possible in water,
ethanol and dichloromethane Deuel et al., Helv. Chim. Acta 1950 33(5) 1229-1232
OO
On
O
O
N OO N O
On
Cl
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Face modification of clay platelets
Face modification of the surface with cationic
molecules did not enable polymerization at the surface
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Starved-feed emulsion polymerization of
edge modified MMT
• A feeded addition of monomer is needed to minimize the formation
of “empty” latex particles
• The content of latex particles containing a clay platelet is between
60-70 % (based on counting with TEM)
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Proposed mechanism
Edge modification Initial polymer
formation at the
edge; donut
structure
Engulfing of the
faces, leading to
Dumbbell/Peanut
shape
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Settling of dumbbell shaped nanocomposites shows that
clay is predominantly lying perpendicular to the substrate
Film formation, where is the clay?
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Monomer/
Initiator
Polymer Shell
The approach
• Synthesize short anionic amphiphilic random macro-RAFT
copolymers
• Adsorb these macro-RAFT agents onto the oppositely
charged substrate
• Initiate polymerization with a fresh supply of initiator and
desired monomer(s)
Nguyen, D.; Zondanos, H. S.; Farrugia, J. M.; Serelis A. K.; Such C.H.; Hawkett, B. S, Langmuir (2008), 24(5), 2140-2150.
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The substrate
•GIBBSITE is chosen because:
•Easy to synthesize
•Particles are monodisperse
•Product easy to image
•Isoelectric point at pH 9 -10
provides ideal working window
for encapsulation
•Encapsulation at pH 7
•Good positive surface charge
for adsorption of negative
macro-RAFT
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Synthesis of random RAFT copolymers
2X = 5BA-co-5AA
CH2
CH2S S
S
CH2
XCH2
X S S
S
+ AA/BA =
• In dioxane using AIBN at 70OC
• RAFT agent: Dibenzyl trithiocarbonate (easy to make;
commercially available)
• RAFT/AIBN = 11
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Shell thickness can easily be controlled!
50% conversion sample 100% conversion sampleSyed Imran Ali, Johan P.A. Heuts, Brian S. Hawkett and Alex M. van Herk.
Langmuir, Accepted for publication. May, 2009
Gibbsite platelets encapsulated with MMA, grown with the BA/AA
macroRAFT agent 5BA-co-5AA and ABCZ as initiator, 70 C
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4-compartment nanoparticle;
Vinegar-oil nanobottle
2-compartment nanoparticle;
Nanobottle
Janus particle
Pimple particle
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Future research
• Morphology and film formation of latex particles
with clay inside (multiphase particles)
• Actual release experiments with the nanobottles
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Acknowledgements
Prof. Brian Hawkett (University of Sydney)
Dr. Marshall (W.) Ming, Prof. Bert de With (TU Eindhoven)
Foundation Emulsion Polymerization (SEP)
Dutch Polymer Institute (DPI)