The presentation shortly shows the research that I did during my Ph.D. at the Eindhoven University of Technology. The aim is the microencapsulation of salt hydrates for their use in heat storage applications. The central question of the research is: "How to use Pickering emulsions efficiently for microencapsulation?"

1. Pickering emulsions,
colloidosomes &
micro-encapsulation
Joris W.O. Salari, 12 May 2011
Ph.D. defense

2. 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.

3. Pickering emulsions
Young’s equation:
Partial or intermediate wetting:

4. Micro-encapsulation
Reinforcement of the particle layer surrounding each droplet
of the Pickering emulsion.

5. Micro-encapsulation
Repulsive
Attractive

6. Wetting & Colloidal stability
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
Langmuir 2011, 27 (11) pp 6574 – 6583

7. Wetting & Colloidal stability
Results SCF calculation:
Wetting (left) & colloidal stability (right) are fundamentally
related for Pickering stabilizers.
Langmuir 2011, 27 (11) pp 6574 – 6583

8. Colloidal cages: colloidosomes
with tunable particle packing

9. 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 :

10. 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)

11. Colloidal cages
Dp = 1.8 µm Dp = 5.0 µm
Increasing particle size
Particle density capsules is incomplete for small particles.
Possible cause: attraction among the particles.
Soft Matter 2011, 7 pp 2033 – 2041 & Physical review E 2012, 85, 061404

12. Colloidal cages
Particle density decreases with the particle diameter.
Rp[mm] Density [-]
5.0 0.98
3.3 0.89
2.7 0.84
1.9 0.75
1.8 0.74
Soft Matter 2011, 7 pp 2033 – 2041 & Physical review E 2012, 85, 061404

13. Colloidal cages
- Attraction leads to aggregation.
- Smaller particles exhibit more irregular aggregates, than
large particles.

14. Steric stabilization of Pickering
emulsions:
pS microcapsules

15. pS microcapsules
Soap-free emulsion
polymerization
Addition of NaCl(aq) to induce interfacial adsorption.
Langmuir 2010, 26 (18) pp 14929 - 14936

16. pS microcapsules
Addition of pS-b-pEP (Kraton)
Adsorption profiles determined by GPC.
Kraton : pS-b-pEP
Langmuir 2010, 26 (18) pp 14929 - 14936

17. pS microcapsules
Heat to 35 ˚C (sintering)
No pS-b-pEP adsorbed: pS-b-pEP adsorbed:
attractive repulsive
Langmuir 2010, 26 (18) pp 14929 - 14936

18. pS microcapsules
Langmuir 2010, 26 (18) pp 14929 - 14936

19. pMMA microcapsules

20. pMMA microcapsules
Particle synthesis: dispersion polymerization of MMA in C7,
with variable steric stabilizer (pIB) concentration.

21. pMMA microcapsules
Hairy Pickering emulsions:
Hairy particles experience significant activation barrier.

22. pMMA microcapsules
Increasing time & conversion of MMA
t=0 t = 90 min

23. pMMA microcapsules
Dutch patent application, NL1038722

24. Micro-encapsulation of CaCl2 6H2O
Properties clearly show effect of micro-encapsulation.
Confined crystallization (DSC) Deliquescence (gravimetry)

25. 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.

26. Acknowledgements
• Prof. dr. ir. L. Klumperman
• Prof. dr. J. Meuldijk
• Prof. dr. A. van Herk
• Ing. Herman Reezigt
Questions?
jorissalari@gmail.com