stabilization and organization, Indo-French Workshop on Multifunctional Molecular and Hybrid Devices 6-10 October 2008, Saint-Aubin

Transcription

1 : emulsion stabilization and organization, Indo-French Workshop on Multifunctional Molecular and Hybrid Devices 6-10 October 2008, Saint-Aubin CEA,IRAMIS,LIONS October 7, 2008

2 Nanochemistry Interfaces, confined fluids and wetting Nanoparticles, nucleation and growth, emulsions, toxicity Charged systems Spraydrying Self-assembly, anionic+cationic surfactants Wetting Interfacial films, amphiphiles, Bio-inspired (charged) mineralization polymers 200 Cage molecules Biophysics Membrane s

3 Outline 1 2 3

4 Nanoparticles as surfactants γ NPw + γ ow cos θ = γ NPo E = πr 2 γ ow (1 ± cos θ) 2 Large attachment energy; stability self-healing for nanoparticles?

5 Pickering emulsions Stability θ < 90 oil in water θ > 90 water in oil Wettability can be tuned by chemically modifying the particle surface Monodispersity (partial coalescence) Materials science aspects Importance of particle-particle interactions

6 Synthesis and surface modification Reduction of HAuCl4 in toluene by sodium borohydride in presence of alkanethiols (tetraoctylammonium bromide = tranfer agent) M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman, J. Chem. Soc., Chem. Commun. 801 (1994) Ligand: hexanethiol partially exchanged with 11-mercapto-1-undecanol ratio 6:1 OH:CH 3 estimated by NMR Radius 1.25 ± 0.3nm

7 Particle-particle interactions Dispersion forces (attractive) Repulsion between ligand shells Coulombic (?) M.K. Bera et al., Europhys. Lett (2007)

8 Compression isotherms and Brewster angle microscopy

9 Grazing incidence diffraction and diffuse scattering ESRF, ID10B, 21.9keV

10 » Z dσ dω = 4π2 r e t in 2 t sc 2 A(be in.be sc) 2 F (q) 2 ρ 1 + 2πρ (g(r ) 1)J 0(q r )r dr + Diffuse scattering F (q) = [sin(qr) qr cos(qr)] qr 3

11 Grazing incidence diffraction d=4.nm (about 8nm in the emulsions), ξ=20nm

12 U Attach (z) = πγ(r + L) 2 z 2 «(R + L) 2 1 (θ = 90%) " U NP NP (d) = k B T 2πR 1R 2 s 3 16 (R 1 + R 2 ) 5 P.G. de Gennes, Adv. Colloid Interf. Sci (1987). (2L) 9/4 (d R 1 R 2 ) 16 (d R 1 R 2 ) 11/4 + 1/4 77 (2L) 3/ (2L(d R 1 R 2 )) (2L)2

13 ΠA = Nk B T 1 3 r ij rij U(r ij ) i j>i

14 X-ray reflectivity R(q z ) = R F 1 (ρ w ρ o ) ( ) ρ z e iqz z dz 2 e q2 z σ2 σ 2 = k BT qmax 2πγ log q min for q < simulation box size

15 In-plane organization

16 In-plane organization N I (q) A V j F j (q)e iq.r j j=1 2

17 Emulsion preparation Addition of oil (tetraor hexadecane) and Particles dispersed in isopropanol (2%-4%) emulsification by ultrasound Removal of the excess oil and dialysis to remove the isopropanol

18 Dynamic light scattering I

19 Confocal microscopy and freeze fracture EM Confocal microscopy (tetradecane) Freeze fracture (hexadecane) Movement reduced by agarose Droplet size 200nm Droplet size 400nm J.-M. Verbavatz, CEA

20 Dynamical light scattering II Size and shape are not changing when the oil solidifies Pronounced change in diffusion when ligand shell solidifies Hexadecane emulsion is more stable than tetradecane Equilibrium hydrodynamic radius R H = 125nm in hexadecane and increases from R H = 140nm to R H = 250nm in tetradecane

21 SAXS measurements SWING beamline, Soleil

22 Outlook 2nm nanoparticles can stabilize emulsions 2D films can be studied in detail at o/w interface Isotherms + Diffraction + MC simulations NP-NP interactions Mechanism of emulsion stabilization?

23 S. Kubowicz, M. Hartmann, M. Dubois Collaboration H. Möhwald (Potsdam) M.K. Sanyal (Calcutta) O. Konovalov, ESRF F. Meneau, J. Perez, O. Lyon, Soleil

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