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Pickering emulsions,
colloidosomes &
micro-encapsulation
Joris W.O. Salari, 12 May 2011
Ph.D. defense
Aim: Encapsulation of salt hydrates Salt hydrates can store large amounts of thermal energy by undergoing a
solid-liquid phase change (phase change materials, PCMs).
Encapsulation allows the incorporation of salt hydrates in construction materials.
Pickering emulsions
Young’s equation:
Partial or intermediate wetting:
Micro-encapsulation
Reinforcement of the particle layer surrounding each droplet
of the Pickering emulsion.
Micro-encapsulation
Attractive
Repulsive
Self-Consistent Field (SCF) theory is used to calculate both
wetting & colloidal stability.
System:
- Heptane/Water (C7/H2O) interface
- Hairy pMMA particle: Rp = 1 mm
- Hairs: polyisobutylene
Wetting & Colloidal stability
Langmuir 2011, 27 (11) pp 6574 – 6583
Results SCF calculation:
Wetting & Colloidal stability
Langmuir 2011, 27 (11) pp 6574 – 6583
Wetting (left) & colloidal stability (right) are fundamentally related for Pickering stabilizers.
Colloidal cages: colloidosomes
with tunable particle packing
Dispersion polymerization
Uniform poly(styrene) particles are synthesized in ethanol/water.
Recipe:
- 83.4 wt% Ethanol
- 14.4 wt% Styrene
- 0.1 wt% Divinylbenzene
- 1.8 wt% PVP40
- 0.3 wt% AIBN
PVP :
Colloidal cages
Formation of colloidosomes
- Disperse particles in C7
- Add H2O
- Shear for 10 s at 10.000 rpm (20.000 s-1) with Ultraturrax®
- Heat to 35 C° (sintering)
Colloidal cages
Particle density capsules is incomplete for small particles.
Possible cause: attraction among the particles.
Dp = 1.8 µm Dp = 5.0 µm
Increasing particle size
Soft Matter 2011, 7 pp 2033 – 2041 & Physical review E 2012, 85, 061404
Colloidal cages
Rp[mm] Density [-]
5.0 0.98
3.3 0.89
2.7 0.84
1.9 0.75
1.8 0.74
Particle density decreases with the particle diameter.
Soft Matter 2011, 7 pp 2033 – 2041 & Physical review E 2012, 85, 061404
Colloidal cages
- Attraction leads to aggregation.
- Smaller particles exhibit more irregular aggregates, than
large particles.
Steric stabilization of Pickering
emulsions:
pS microcapsules
pS microcapsules
Soap-free emulsion
polymerization
Addition of NaCl(aq) to induce interfacial adsorption.
Langmuir 2010, 26 (18) pp 14929 - 14936
pS microcapsules
Addition of pS-b-pEP (Kraton)
Adsorption profiles determined by GPC.
Langmuir 2010, 26 (18) pp 14929 - 14936
Kraton : pS-b-pEP
pS microcapsules
Heat to 35 ˚C (sintering)
No pS-b-pEP adsorbed: attractive
pS-b-pEP adsorbed: repulsive
Langmuir 2010, 26 (18) pp 14929 - 14936
pS microcapsules
Langmuir 2010, 26 (18) pp 14929 - 14936
pMMA microcapsules
pMMA microcapsules
Particle synthesis: dispersion polymerization of MMA in C7,
with variable steric stabilizer (pIB) concentration.
pMMA microcapsules
Hairy Pickering emulsions:
Hairy particles experience significant activation barrier.
pMMA microcapsules Increasing time & conversion of MMA
t = 0 t = 90 min
pMMA microcapsules
Dutch patent application, NL1038722
Micro-encapsulation of CaCl2 6H2O
Properties clearly show effect of micro-encapsulation.
Confined crystallization (DSC) Deliquescence (gravimetry)
Conclusion
• Encapsulation of salt hydrates is successful.
• Study revealed important parameters for a successful &
efficient micro-encapsulation from Pickering emulsions.
• Wetting & colloidal stability are fundamentally related in the
case of Pickering stabilization.
Acknowledgements
• Prof. dr. ir. L. Klumperman
• Prof. dr. J. Meuldijk
• Prof. dr. A. van Herk
• Ing. Herman Reezigt
Questions? [email protected]
