Lipid functionalised Polyelectrolyte Multilayers Studied by Neutron Reflectometry

Transcription

1 Lipid functionalised Polyelectrolyte Multilayers Studied by Neutron Reflectometry R. Krastev, N. Ch. Mishra, Chr. Delajon, H. Möhwald Max-Planck Institute of Colloids and Interfaces, Golm/Potsdam Th. Gutberlet Paul Scherrer Institute, Villigen PSI, Switzerland

2 utline - Neutron reflectometry basics of the method - What can we learn using the method? -Vapour distribution in composite polymer films used as chemical sensors -Controlled water permeability in polyelectrolyte films -In-situ control of the film build-up process - Structure of polyelectrolyte multilayers covered with lipids and polyelectrolyte/lipid/polyelectrolyte sandwich like composites

3 Neutron reflectometry I i I i Q Q θ 1 I r I r 10 θ 1 θ 1 θ 1 θ θ 1 2 θ 3 θ 2 d E-3 1E-4 Substrate/air Substrate/film/air: interface: k o F R R = ff( ( ko, ks ) o, s, k f, d ) ( 2 ; k4 sπρ = o) π = 2 k sinθ 2 f = k f λ o ( k 4πρ ) s 1E-5 1E Q, Å -1

4 Neutron reflectometry 1 The film thickness - The Scattering Length Density (ρ) - = i i ( z) b N ( z) The surface roughness (σ) - ρ n ρ ( z ) > 0 ; ρ ( z ) < 0 n ρ film ( x) 2 = xρ ρ b D = 6.67x10-6 Å b H = -3.74x10-6 Å E-4 1E E-4 1E Q,Å E-4 Q,Å -1 1E Q,Å -1

5 Neutron reflectometry - Experiment detector θ 2θ sample Source:

6 Vapour distribution in chemical sensors etc E-3 1E-4 Nanoparticle Dendrimer Amino-Silane Glass Substrate (electrode structures) 2. Cycle 1. Cycle Wet film ρ(z), Å -2 4x10-6 3x10-6 2x10-6 1x10-6 substrate film gas 1E Q, Å -1 Dry film Film thickness (z), Å N. Krasteva, et al Langmuir 19 (2003) 7754 Small incorporation of vapours in the film and formation of wettin layer on top

7 Neutron reflectometry - Experiment I i Q Single Si crystal I r θ 1 θ 1θ2 θ 1 D 2 θ 3 Teflon block The neutron reflectometry allows to probe liquid/solid interfaces

8 Controlled water permeability in polyelectrolyte films Wax particles 7.0x x10-6 substrate film D 2 Heating Barrier layer SLD, Å x x x x Film thickness, nm K. Glinel et al Langmuir 20 (2004) 4898 Incorporation of wax particles hinders the water penetration in the film

9 In-situ controlled Layer-by-Layer deposition deionised water PAH PSS Lipid layer deionised water

10 Formation of DMPC bilayer on PEM SLD 100 Si 1 After DMPC deposition PEM E-4 1E-6 1E-8 Bare PEM block Q z, Å -1 Z DMPC Si D 2 SLD PEM D 2 Z

11 Formation of DMPC bilayer on PEM SLD (x10 6 Å -2 ) Before lipid deposition After lipid deposition Si PEM DMPC D Thickness, nm h~5 DMPC bilayer with a thickness o 5 nm is formed

12 Adsorption of DMPC on positively terminated PEM After lipid deposition Before lipid deposition Q z (nm -1 ) DMPC does not form smooth bilayers on positively charged PEM

13 How does DMPC interact with PEM? P N DMPC molecules electrostatically interact with the PEM

14 PEM/DMPC/PEM sandwich like structures Q z (nm -1 ) PEM/lipid/PEM sandwich like structures are possible

15 Conclusions 1. Neutron reflectometry is a powerful method to study polymer films at solid interfaces. 2. The vapour distribution in composite polymer films used as chemical sensors was described. 3. The action of wax particles to control the water permeability in PEM was represented. 4. The LbL build-up process was in-situ controlled. 5. Formation of PEM/lipid complexes and PEM/lipid/PEM sandwich like structures was proved.