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Design of Pickering Emulsion Templated Colloidosomes and Fundamentals of
Emulsification with Nanoparticles
IPST Members Meeting
Hongzhi Wang
Sven Research Group
April 10,2012
Research Overview
Dual research
Design microcapsules
Fundamentals of Pickering emulsions
Design pH responsive composite microcapsules for controlled release
of antimicrobial cargoes
Investigate effects of particle charge on Pickering emulsions that are
neglected in conventional theory
Design colloidosomes: motivation and objective
Colloidosomes are semi-permeable microcapsules whose external shell is formed by colloid particles.
Aim to design composite pH responsive colloidosomes for controlled release
Colloidosomes represent a promising encapsulation technology with good controllable permeability, mechanical properties and bio-compatibility.
R. Aveyard, B. P. Binks, J. H. Clint, Advances in Colloid and Interface Science 2003, 100-102, 503-546.
Pickering emulsions
Phase I
Phase II
OWOW AG
VS
B.P. Binks, Current Opinion in Colloid and interface Science, 7, 21 (2002)
Adsorption energy ∆E>> kT
Irreversible adsorption
θ<90º hydrophilic o/w
θ>90º hydrophobic w/o
θ<90º θ=90º θ>90º
Water
Oil
R. Aveyard, B. P. Binks, J. H. Clint, Advances in Colloid and Interface Science 2003, 100-102, 503-546.
Design Protocol
Explore double Pickering emulsion as template
Experimental observation
The water phase is labeled with FITC-dextran (10 kDa) encapsulated (green zone) , while the oil phase is not labeled.(black zone)
By rational design of the shell composition, we are able to generate colloidosome capsules with different release properties.
pH responsive colloidosomes FITC-dextran (10KDa) was encapsulated inside
Fast release : ~3s
Stepwise release : ~30s My research focus:
Composite colloidosomes with a sustainable release
fashion
Composite pH responsive colloidosomes
• The shell permeability can be controlled by adjusting the shell thickness and adding polymer matrix.
Hybrid pH responsive colloidosomes with a long-lasting release profile are generated by the inclusion of inorganic particles and polymeric particles
Thin shell Thick shell Incorporate
polymer matrix
• The size range of colloidosomes is 20 – 60 mm
Permeability Evaluation
• The permeability of hybrid colloidosomes for 10 kDa FITC-dextran is evaluated by fluorescence recovery after photo bleaching (FRAP).
0 100 200 300 400 500 600 700 800 900 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
time/s
f(t)
/arb
itry
units
Frap cruve for 10kDa FITC-labeled dextran
before release triggerred
After release triggered
Increase pH
http://en.wikipedia.org/wiki/Fluorescence_recovery_after_photobleaching
Envisioned applications
Antimicrobial colloidosomes
Encapsulate antimicrobial inside
Stimulus trigger
Sustainable antimicrobial protection
Fundamentals of emulsification with polymeric nanoparticles
Motivation and objective
Motivation: Current fundamental understanding is far
from satisfactory, which limits the applications!
Objective: Explore the important factors affecting
Pickering emulsions that are neglected in conventional theory by investigating emulsification with charged latex particles
-COOH -COO- + H+ pH Carboxyl
-C(=NH)NH2 -C(=NH2)NH2 pH Amidine + H+
+
Our experimental findings
No emulsions form when polymer particles are highly charged under low salt concentration
10-4
10-3
10-2
10-1
100
101
0
1
2
3
4
5
6
7
8
9
10
11
12
13
incre
ase
d in
terf
acia
l ch
arg
e
w/o
o/w
No emulsion
Increased screening
incre
ase
d c
ha
rge
de
nsity
Electrolyte concentration/M
pH
Particles with macroscopic contact angle greater than 90º should stabilize w/o emulsions
10-4
10-3
10-2
10-1
100
101
12
11
10
9
8
7
6
5
4
3
2
1
incre
ased
in
terf
acia
l ch
arg
e
incre
ase
d c
ha
rge
de
nsity
Increased screening
o/wNo emulsion w
Electrolyte concentration/M
pH
Hypothesis and supporting evidence
Repulsion! Electrical repulsive force including double layer force and image force can impede adsorption of particle to the interface to stabilize emulsions
The repulsive force are expected to cause a deformation when the interface is very close to the particle
Self energy of particle counter-ion dipole causes shift in equilibrium particle position and leads to a different contact angle in the interface from macroscopic contact angle
θ<90º
3D
Hypothesis and supporting evidence
Conclusions
We explore double Pickering emulsions as precursors for composite pH-responsive colloidosome for customizable release control
We propose the electrostatic interaction between the particle and interface, including electrical double layer force and image force, can impede the particle adsorption and therefore affect the emulsion formation.
The self-energy of the particle-counterion dipole can shift the particle’s equilibrium position toward the water phase and yield a modified contact angle and emulsion type not predicted from macroscopic contact angle measurements.
Acknowledgements
• Funding from IPST through a PSE fellowship and from the National Science Foundation
• Professors Toan Nguyen, Professors Jennifer Curtis
• Dr. Jan Scrimgeour, Dan Kovari
Thank you !