phd_joris salari

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? jorissalari@gmail.com