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
Functionalities
Suprastructures
Polymer Colloids
Polymer Colloids = Latex particles are nanosized
polymer particles, colloidally stabilized (usually) in water.
1nm
100nm
Main production methods: -Emulsion polymerization
-Miniemulsion polymerization (77)
Main applications: -Water-borne Coatings (paper/architectural/car)
-Water-borne Adhesives
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Production techniques
μm
Emulsion polymerization
nm
Miniemulsion polymerization
nm
Microemulsion polymerization
nm
μm
Suspension polymerization
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Encapsulation in aqueous media
Molecules
LBL Driving force: Charges/Other
addapted from Mohwald Internet source
Particles
Emulsion polymerization
Driving force: Water Insolubility
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Controlled Release Profiles
Concentration
Release of drugs, crosslinking agents, anticorrosive agents etc.
Pulse
Time
Continuous release,
often based on
(bio)degradation of
polymer.
Pulse
Time
Pulsatile response,
based on external
trigger pulse, e.g.
pH, Ultrasound,
heat. Release per
pulse not constant.
Pulse
Pulse
Time
Pulsatile response,
based on external
trigger pulse, e.g.
pH, Ultrasound,
heat. Release per
pulse constant.
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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 5070 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
Ddif
Multicompartment nanoparticle where
all compartments are the same; Pimple
particle
Dtar
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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; Janus particle
Nanobottle
4-compartment nanoparticle;
Vinegar-oil nanobottle
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Vesicles as a route towards multicompartment
nanoparticles
swell bilayer
with monomer
polymerize
Nanobottles
Jung et al. Langmuir 1997, 13, 6877; Langmuir 2000, 16, 968.
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application of polymerisable amphiphiles
+ crosslinking amphiphiles
+ styrene
100 nm
100 nm
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Influence of initiator.
H3N
Cl
The “matrioshka” architecture
HN
On the way towards Vinegar-oil nanoparticles
thermal polymerisation at 60°C, V50
100 nm
N N
NH3
NH
Cl
Vesicle Polymerization…
Some new morphologies.
Nanobottles
Styrene
Pimple particles
Butyl acrylate
Pimple particles
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
Spherical
particles
• Anisotropic (preferably flat) latex particles can induce anisotropy into the
final film and this would significantly improve the final properties
Flat
particles
• For example, barrier properties might be expected to improve because clay
platelets align parallel to the substrate during film formation
Challenges in Clay encapsulation
through emulsion polymerization
Secondary
nucleation
Stacking
Armoured
latex
particles
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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
O
O
O
n
O
O
N
O
O
n
O
N
Cl
O
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
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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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Film formation, where is the clay?
Settling of dumbbell shaped nanocomposites shows that
clay is predominantly lying perpendicular to the substrate
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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)
Polymer Shell
Monomer/
Initiator
Nguyen, D.; Zondanos, H. S.; Farrugia, J. M.; Serelis A. K.; Such C.H.; Hawkett, B. S, Langmuir (2008), 24(5), 2140-2150.
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
Synthesis of random RAFT copolymers
• In dioxane using AIBN at 70OC
• RAFT agent: Dibenzyl trithiocarbonate (easy to make;
commercially available)
• RAFT/AIBN = 11
S CH2
CH2 S
+ AA/BA =
S
CH2 X S
S
S
2X = 5BA-co-5AA
X CH2
Shell thickness can easily be controlled!
Gibbsite platelets encapsulated with MMA, grown with the BA/AA
macroRAFT agent 5BA-co-5AA and ABCZ as initiator, 70 C
50% conversion sample
100% conversion sample
Syed Imran Ali, Johan P.A. Heuts, Brian S. Hawkett and Alex M. van Herk.
Langmuir, Accepted for publication. May, 2009
2-compartment nanoparticle;
Nanobottle
Janus particle
Pimple particle
4-compartment nanoparticle;
Vinegar-oil nanobottle
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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)
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