PhD_Joris Salari

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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?"

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PhD_Joris Salari

  1. 1. Pickering emulsions, colloidosomes &micro-encapsulationJoris W.O. Salari, 12 May 2011 Ph.D. defense
  2. 2. Aim: Encapsulation of salt hydratesSalt hydrates can store large amounts of thermal energy by undergoing asolid-liquid phase change (phase change materials, PCMs). Encapsulation allows the incorporation of salt hydrates in construction materials.
  3. 3. Pickering emulsions Young’s equation:Partial or intermediate wetting:
  4. 4. Micro-encapsulationReinforcement of the particle layer surrounding each droplet of the Pickering emulsion.
  5. 5. Micro-encapsulation RepulsiveAttractive
  6. 6. Wetting & Colloidal stabilitySelf-Consistent Field (SCF) theory is used to calculate bothwetting & colloidal stability.System:- Heptane/Water (C7/H2O) interface- Hairy pMMA particle: Rp = 1 mm- Hairs: polyisobutyleneLangmuir 2011, 27 (11) pp 6574 – 6583
  7. 7. Wetting & Colloidal stabilityResults SCF calculation:Wetting (left) & colloidal stability (right) are fundamentallyrelated for Pickering stabilizers.Langmuir 2011, 27 (11) pp 6574 – 6583
  8. 8. Colloidal cages: colloidosomes with tunable particle packing
  9. 9. Dispersion polymerizationUniform poly(styrene) particles are synthesized inethanol/water.Recipe:- 83.4 wt% Ethanol- 14.4 wt% Styrene- 0.1 wt% Divinylbenzene- 1.8 wt% PVP40- 0.3 wt% AIBN PVP :
  10. 10. Colloidal cagesFormation 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. 11. Colloidal cagesDp = 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. 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 0.74Soft Matter 2011, 7 pp 2033 – 2041 & Physical review E 2012, 85, 061404
  13. 13. Colloidal cages- Attraction leads to aggregation.- Smaller particles exhibit more irregular aggregates, than large particles.
  14. 14. Steric stabilization of Pickering emulsions: pS microcapsules
  15. 15. pS microcapsulesSoap-free emulsionpolymerizationAddition of NaCl(aq) to induce interfacial adsorption.Langmuir 2010, 26 (18) pp 14929 - 14936
  16. 16. pS microcapsulesAddition of pS-b-pEP (Kraton)Adsorption profiles determined by GPC. Kraton : pS-b-pEPLangmuir 2010, 26 (18) pp 14929 - 14936
  17. 17. pS microcapsules Heat to 35 ˚C (sintering) No pS-b-pEP adsorbed: pS-b-pEP adsorbed: attractive repulsiveLangmuir 2010, 26 (18) pp 14929 - 14936
  18. 18. pS microcapsulesLangmuir 2010, 26 (18) pp 14929 - 14936
  19. 19. pMMA microcapsules
  20. 20. pMMA microcapsulesParticle synthesis: dispersion polymerization of MMA in C7,with variable steric stabilizer (pIB) concentration.
  21. 21. pMMA microcapsulesHairy Pickering emulsions:Hairy particles experience significant activation barrier.
  22. 22. pMMA microcapsules Increasing time & conversion of MMA t=0 t = 90 min
  23. 23. pMMA microcapsulesDutch patent application, NL1038722
  24. 24. Micro-encapsulation of CaCl2 6H2OProperties clearly show effect of micro-encapsulation. Confined crystallization (DSC) Deliquescence (gravimetry)
  25. 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. 26. Acknowledgements• Prof. dr. ir. L. Klumperman• Prof. dr. J. Meuldijk• Prof. dr. A. van Herk• Ing. Herman Reezigt Questions? jorissalari@gmail.com

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