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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
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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
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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
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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
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Functionalization of the CNCs
DMSO CNCs Vinyl acetate K2CO3 Reagents are mixed using ultrasound. Use of microwave reactor at 80°C under stirring. 5
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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
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Functionalization of the CNCs
Characterization of the modified CNCs – Fourier Transform InfraRed spectroscopy sC-O) 1060cm-1 CNC acetate as (O-(C=O)) cm-1 sC=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
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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
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Elaboration of emulsions
Sonication tip Polymerization can then be performed. 9
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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
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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.
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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
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Impact of the CNCs concentration
Target : low dispersity and small droplets. The chosen [CNCs] is 5mg/mL. Uncontrolled area Limited coalescence area
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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
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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
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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 ± 5,3m PMMA emulsion D3,2 = 17,9 m ± 2,8m The polymerized beads are present. There is no coagulate. Mn = g/mol Ip = 2,83
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Polymerization of emulsions
H1 NMR of PMMA b a Yield = 96% c cpolym CDCl3 a b cmono
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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.
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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)
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Thank you for your attention
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