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 !