phd_joris salari
DESCRIPTION
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?"TRANSCRIPT
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Pickering emulsions,
colloidosomes &
micro-encapsulation
Joris W.O. Salari, 12 May 2011
Ph.D. defense
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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.
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Pickering emulsions
Young’s equation:
Partial or intermediate wetting:
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Micro-encapsulation
Reinforcement of the particle layer surrounding each droplet
of the Pickering emulsion.
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Micro-encapsulation
Attractive
Repulsive
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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
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Results SCF calculation:
Wetting & Colloidal stability
Langmuir 2011, 27 (11) pp 6574 – 6583
Wetting (left) & colloidal stability (right) are fundamentally related for Pickering stabilizers.
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Colloidal cages: colloidosomes
with tunable particle packing
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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 :
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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)
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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
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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
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Colloidal cages
- Attraction leads to aggregation.
- Smaller particles exhibit more irregular aggregates, than
large particles.
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Steric stabilization of Pickering
emulsions:
pS microcapsules
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pS microcapsules
Soap-free emulsion
polymerization
Addition of NaCl(aq) to induce interfacial adsorption.
Langmuir 2010, 26 (18) pp 14929 - 14936
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pS microcapsules
Addition of pS-b-pEP (Kraton)
Adsorption profiles determined by GPC.
Langmuir 2010, 26 (18) pp 14929 - 14936
Kraton : pS-b-pEP
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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
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pS microcapsules
Langmuir 2010, 26 (18) pp 14929 - 14936
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pMMA microcapsules
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pMMA microcapsules
Particle synthesis: dispersion polymerization of MMA in C7,
with variable steric stabilizer (pIB) concentration.
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pMMA microcapsules
Hairy Pickering emulsions:
Hairy particles experience significant activation barrier.
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pMMA microcapsules Increasing time & conversion of MMA
t = 0 t = 90 min
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pMMA microcapsules
Dutch patent application, NL1038722
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Micro-encapsulation of CaCl2 6H2O
Properties clearly show effect of micro-encapsulation.
Confined crystallization (DSC) Deliquescence (gravimetry)
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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.
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Acknowledgements
• Prof. dr. ir. L. Klumperman
• Prof. dr. J. Meuldijk
• Prof. dr. A. van Herk
• Ing. Herman Reezigt
Questions? [email protected]