Raman and AFM characterization of carbon nanotube polymer composites Illia Dobryden

Transcription

1 Raman and AFM characterization of carbon nanotube polymer composites Illia Dobryden

2 This project is conducted in High Pressure Spectroscopy Laboratory (Materials Physics group) Supervisor: Professor Alexander Soldatov

3 Introduction Outline General Introduction to carbon nanotubes. Raman spectroscopy of CNTs. Introduction to carbon nanotube composites. Functionalization of carbon nanotubes. Marerials and methods Results Distribution of CNTs in the composite. Interaction between CNTs and the composite matrix. The qualitative estimation of CNTs amount in the polymer matrix. FIB polishing and AFM experiments. Conclusions and Future Work

4 Carbon Nanotube (CNT) Graphene layer roll-up Diameter: < 1 nm up to tens of nm Lenght: < 1 μm up to even several mm High aspect ratio (Lenght/diameter) up to > Considered as 1D material Extraordinary mechanical, electrical, thermal properties

5 Types of carbon nanotubes Single-wall CNT only one atomic layer in radial direction - Metallic and semi conducting - Tend to agglomerate in bundles - Entangled Single-wall CNT Double-wall CNT two atomic layers in radial direction - Good model system to study intertube interactions - Pressure screening of inner tubes by outer tubes - Reinforcement of outer tubes by inner tubes - Much more resistant to high pressures Double-wall CNT Multi-wall CNT several atomic layers in radial direction - Always electrically conductive (metallic behavior) - Entangled - Much bigger diameters than SWNTs Multi-wall CNT

6 Physical properties Property MWNT Carbon fibre Steel Kevlar Young s Modulus [Gpa] Tensile strenght [GPa] , El. Conductivity [S/m] Thermal conductivity [W/mK] Individual or bundled CNTs CNT films or fibres Silver Copper SWNT MWNT Carbon fibres Silver Copper

7 Resonance Raman Spectroscopy G - band Radial breathing mode (RBM) CNT diameter: RBM A B dt

8 Composites The Main idea: combine good properties of two or more materials. Composite Matrix (Metal, Ceramic, polymer) Filler material (particles, fibers etc) CNTs are the good candidates as the filler material because they have great mechanical, electric properties. Possible problems in using CNTs as the filler material: 1. CNTs exist in bundle state. 2. Bad interaction between CNTs and the composite matrix. 3. It is difficult to get a good dispersion in the composite.

9 Composites Possible Solutions: 1. - Good dispersion by ultrasonication Functionalization of CNTs. Main idea behind functionalization: Covalent attachment of molecules which will has a good link with the matrix material to CNT surface. In situ polymerization has been done with CNTs in the polymer matrix CNTs in our composite: three-step chemical approach to functionalize SWNTs (performed at Henri Pointcaré Univeristy, Nancy)

10 Project motivation Synthesis and Characterization of the new composite material based on functionalized carbon nanotubes Raman spectroscopy proved to give various information about CNT systems Atomic Force Microscopy (AFM) For direct microstructural study

11 Materials and Methods Materials: - Arc-discharge three step functionalized CNTs (performed at Henri Pointcaré University, Nancy (France) - PMMA (Polymethylmetacrylate) Methods: - The Confocal Raman Spectroscopy Raman spectrometer CRM-200, - a green NdYVO4 diode laser (532 nm, 2,33 ev) - a red He-Ne laser (633 nm, 1,96 ev ) - Focused Ion Beam (FIB) - Atomic Force Microscopy (AFM) We have investigated the PMMA composites with CNTs concentrations: 0,013wt%, 0,023wt%, 0,032wt%, 0,048wt%, 0,08wt%, 0,097wt%and 0,6wt%.

12 Results Distribution of CNTs in the composite laser laser laser laser Raman spectrum at every scanning point Sample surface

13 Results Distribution of CNTs in the composite laser laser laser laser The Cluster Sample surface The Matrix

14 Raman spectra of composite and source materials Normalized to highest peak Intensity (a.u.) R a m a n s h ift (re l. cm -1 ) C N T C lu s te r In te rp h a s e M a trix P M M A

15 Distribution of CNTs in the composite a) b) c) d) e) Image : G + - intensity maps for a) 0.013wt%, b) 0.023wt%, c) 0.048wt%, d) 0,097wt% and e) 0,6wt% CNT PMMA composites, 2.33eV laser excitation

16 Interaction between CNTs and the composite matrix The Idea: - The good composite sample must has quite good interaction between the filler material and the composite matrix. G Shift gives information about: Pressure on CNTs (upshift) Tensile stress of CNTs (downshift) Temperature of CNTs (downshift) Intensity proportional to CNT concentration - We expect that the CNT G-band shifts for Functionalized CNTs (FCNTs) the polymer matrix comparing to pure FCNTs due to interaction between the matrix and FCNTs.

17 Dependence of the CNT G-band shift in the PMMA matrix vs CNT concentration There is G UpShift on the graph. It indicates that the PMMA matrix applies pressure on FCNTs.

18 FIB polishing for AFM experiments Polishing of surface for AFM studies a ) b ) Pt SEM images untreated surface FIB polished surface untreated surface 300 nm 835 nm 13.5 ±0.3 μm AFM image

19 AFM experiment AFM image Crossection Image White dot diameters: 10 40nm 20 nm 10nm 19nm 19nm 19 nm 22nm Height view SEM image

20 Conclusions Distribution of CNTs in PMMA composite is inhomogenious. There is an indication that the matrix molecules surrounding the CNTs exert pressure on the nanotubes. The CNT bundle size in the polymer matrix is ~ 20 nm.

21 Future work Further AFM experiments (nano-indentation) to determine mechanical properties of the composites Spectroscopic study of thermal effects in CNT-PMMA composites exposed to high power laser irradiation Increase of CNT dispersion in polymer matrix via purification of functionalized CNT (from non-functionalized)

22 Collaboration/Acknowledgements International Graduate School PhD Polis (TFN LTU) in collaboration with Prof. Edward McRae and Prof. Brigitte Vigolo Carbon Materials group, Nancy University: Associate Prof. Nils Almqvist (AFM experiments) Andreas Müller, former group member (now at MPI Stuttgart) Guillaume Chevennement (EEIGM project student)