1. Polymerization of reactive Pickering Emulsions based on functionalized cellulose nanocrystals
Presented by Arthur Werner, 1rst year PhD student
Directed by Dr. G. Sèbe and Dr. V.Heroguez 1

2. Pickering Emulsions Pickering particles can be : W. Ramsden
Solid particles exhibiting amphiphilic properties
Pickering particles can be :
W. Ramsden
S.U. Pickering
Janus round particles
(treated silica, copolymers…)
Particles
Desorption energy >> KBT
Stable emulsion
Monodispersity
Larger range of size
Less toxic than emulsifiers
Disk-shaped particles
(clays…)
Surfactants
Rod-like particles 2

3. Cellulose NanoCrystals CNCs
Softwood pulp cellulose
Acidolysis with
sulfuric acid (H2SO4)
Negatively charged CNC
Length : 150 nm
Width : 8 nm
Supplied by the university of Maine,
Sulfated CNCs, 1,05 w/w sulfur content
Average
Exhibit hydrophobic plan (200) and hydrophilic plans (others).
y. Habibi Chem. Rev. 2010, 110, 3479–3500
These crystals are good candidates to stabilize pickering emulsions :
CNCs are generally too hydrophilic to stabilize all kinds of o/w emulsion.
Kalashnikova, I., et al., Soft Matter, (3): p
Emulsification of highly hydrophobic oil with 3D network unmodified CNCs. 3

4. Emulsion based on functionalized CNCs
Functionalization of the CNCs
Acetylation OH
AcO OH OH
AcO
OAc OH
OAc
Ac = OH
The hydrophobic/hydrophilic balance can be controlled by the grafting yield.
M. Jebrane, G. Sèbe, Carbohydrate Polymers 72 (2008) p. 657–663.
Conducted in DMSO with K2CO3 catalyst. The vinyl alcohol is degraded which moves the equilibrium towards the products.
Emulsification and polymerization of the Methyl MethAcrylate (MMA), a model monomer.
Functionalization and emulsification
Polymerization
MMA in water

5. Functionalization of the CNCs
DMSO
CNCs
Vinyl acetate
K2CO3
Reagents are mixed using ultrasound.
Use of microwave reactor at 80°C under stirring. 5

6. Functionalization of the CNCs
Purification steps
Mixture after reaction
Precipitation with THF and diethyl ether
Centrifugation step
Redispersion in water
Reprecipitation with THF and diethyl ether
Centrifugation and recuperation of the CNCs
2-3 cycles
Obtention of clean dry acetylated CNCs in less than 24h, with over 90% yield.
Freeze-dryer 6

7. Functionalization of the CNCs
Characterization of the modified CNCs – Fourier Transform InfraRed spectroscopy
sC-O) 1060cm-1
CNC
acetate
as (O-(C=O)) cm-1
sC=O) 1750cm-1
s (C-H3) 1360cm-1
35 min reaction CNCs
25 min reaction CNCs
18 min reaction CNCs
Unmodified CNCs
wt% acetyl = (IC=O/IC-O)/0.0282
Ac (%) = [wt% acetyl x 162 x 100]/[3 x 43 x (100 - wt% acetyl)]
32% molar after 18 min
35% molar after 25 min 50,5% molar after 35 min
P.Tingaut, T.Zimmermann, F.Lopez-Suevos. Biomacromolecules, 2010, 11 (2), pp 454–464 7

8. Functionalisation of the CNCs
Transmission electronic microscopy
After the acetylation reaction, CNCs keep their nanorod structure…
L = 152 ± 15 nm
w = 13 ± 2 nm
…and their negative charge.
Zeta potential :
unmodified CNCs : -60,7 mV
35 min acetylated : -41,1 mV
Properties of the CNCs slightly change.
35 min acetylated CNCs

9. Elaboration of emulsions
Sonication tip
Polymerization can then be performed. 9

10. Impact of acetylation level
Emulsion stability after 4 months…
unmodified CNCs
Acetylated CNCs
18 min
Acetylated CNCs
25 min
Acetylated CNCs
35 min
Demixed emulsion
Emulsion remains stable over time.
Emulsion remains stable over time.
Emulsion remains stable over time.
Acetylated CNCs can stabilize MMA : the hydrophilic/hydrophobic balance has been modified. 10

11. Impact of acetylation level
Under the microscope…
Acetate 18 min emulsion, 32% acetylation
Acetate 35 min emulsion, 50,5% acetylation
Stable
Not stable
During dilution to observe our systems, MMA escaped from 35 min acetylated CNCs emulsion.
The surface wettability of the min acetylated CNC emulsion isn’t appropriate.
Our work will be focused on the 18 min acetylated CNCs.

12. Impact of the CNCs concentration
After stirring
Adsorption of particles
Uncontrolled area
After stirring
Adsorption of particles
Limited coalescence area
Limited coalescence
Coalescence
Limited coalescence
Coalescence
Monodisperse droplets
Polydisperse droplets 12

13. Impact of the CNCs concentration
Target : low dispersity and small droplets.
The chosen [CNCs] is 5mg/mL.
Uncontrolled area
Limited coalescence area

14. Polymerization of emulsions
Radical polymerization: no atmosphere control. MMA and initiator are purified.
Initiator : V70 (AIBN derivative)
t1/2 = 10h at 35°C.
The polymerized beads can then be characterized.
24 h
35°C

15. Polymerization of emulsions
35°C, 24h
Coagulate
MMA in water, [CNC] = 5mg/mL of MMA
PMMA in water, [CNC] = 5mg/mL of MMA
- No beads can be seen by optic microscopy.
Monomer/oligomer probably escaped from the beads because the MMA is slightly soluble in water.
Necessary to increase bead coverage.
Ionic repulsions between CNCs create the net structure.
Addition of NaCl to limit the repulsions.
Cryo SEM picture of acetylated CNC shell

16. Polymerization of emulsions
Addition of salt
Polymerization
35°C, 24h
MMA in water, [CNC] = 5mg/mL of MMA, [NaCl] = 50 mmol
PMMA in water, [CNC] = 5mg/mL of MMA, [NaCl] = 50 mmol
MMA emulsion D3,2 = 20,2 m ± 5,3m
PMMA emulsion D3,2 = 17,9 m ± 2,8m
The polymerized beads are present.
There is no coagulate.
Mn = g/mol
Ip = 2,83

17. Polymerization of emulsions
H1 NMR of PMMA b a
Yield = 96% c
cpolym
CDCl3 a b
cmono

18. Conclusions Perspectives
- We succesfully used acetylated CNCs as Pickering particle :
Tunable hydrophobic/hydrophilic balance.
Dimensions remains the same before/after reactions.
- We kept stable a MMA emulsion :
Time and dilution stable.
- Polymerization has been successful under the right conditions.
Possibility to modify the coverage.
High yield polymerization achieved.
No coagulates.
Perspectives
- Graft other molecules to improve the coverage
and tune the amphiphily :
- Try a wide range of monomers with different hydrophobicities.

19. Bordeaux Imaging Center
Remerciements
Aknowledgements
Advisors
LCPO team and staff
Bordeaux Imaging Center
Dr. Gilles Sèbe
Dr. Valérie Héroguez
(Polymerization part)
Medhi Neqal
Margot Stasse
Robert Ngo
Benjamin Duhiège
Jeremy Brand
Amélie Vax
Bernadette Guillabert
Loïc Petrault
Mélina Pétrel
(TEM)
Placamat
Philippe Legros
(Cryo SEM)
CRPP
Dr. Veronique Schmitt
(Pickering part)

20. Thank you for your attention20