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PPC 10, Smolenice 2011

PPC 10, Smolenice 2011. Positron annihilation and free volume in polymer-solid interfaces and in nanocomposites. Klaus Rätzke, Stephan Harms, Franz Faupel Technische Fakultät der Universität Kiel, Institut für Materiawissenschaft - Materialverbunde Kaiserstr. 2, 24143 Kiel, Germany

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PPC 10, Smolenice 2011

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  1. PPC 10, Smolenice 2011 Positron annihilation and free volume in polymer-solid interfaces and in nanocomposites Klaus Rätzke, Stephan Harms, Franz Faupel Technische Fakultät der Universität Kiel, Institut für Materiawissenschaft - Materialverbunde Kaiserstr. 2, 24143 Kiel, Germany e-mail: kr@tf.uni-kiel.de

  2. Polymeric Materials, Free Volume fuel cell driven submarine barnacles color map: carbon oxygen nitrogen hydrogen fluorine Yacht during kiel week Free volume, important for diffusion, viscosity, adhesion

  3. Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam (PLEPS @ NEPOMUC) Thin Films (SPP Polymer-solid interfaces and Interphases) evaporated and spin coated Teflon AF on Si-Wafer change of free volume due to solid substrate, (coiling changed?) Polymer Nanocomposites free volume as function of filler concentration, mixing rule and side effects Summary

  4. Our toolbox Schematic of free volume distribution Hole Radius (nm) „our toolbox“ positronium lifetime 3  measure for average free volume width of lifetime distribution 3 measure of width of free volume distribution Orthopositronium intensity I3 positronium formation probability * concentration of free volume Moderated pulsed positron beam  depth resolution possible

  5. Positron beam at FRM II in Munich NEPOMUC: Neutron induced Positron source Munich (Christoph Hugenschmidt) PLEPS: Pulsed Low Energy Positron System (Werner Egger, Peter Sperr) median implantation depth: FWHM: J. Algers, P. Sperr, W. Egger, G. Kögel, F. Maurer Phys. Rev. B (2003)

  6. Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam (PLEPS @ NEPOMUC) Thin Films (SPP Polymer-solid interfaces and Interphases) evaporated and spin coated Teflon AF on Si-Wafer change of free volume due to solid substrate, (coiling changed?) Polymer Nanocomposites free volume as function of filler concentration, mixing rule and side effects Summary

  7. schematic of polymer-solid contact property bulk value Inter- phase { solid polymer nanocomposite increased contribution from interphase z key property: free volume char. length scale nm - µm • SPP 1369 interfaces and Interphases • controlled preparation • property profiling • modeling and simulation Here: Free volume of Teflon AF 2400 as a function of distance to interface S. Harms, K. Rätzke, V. Zaporojtchenko, F. Faupel, W. Egger, L. Ravelli, Polymer, 52 (2011) 505

  8. Teflon AF 2400 evaporated onto Si Teflon AF 2400 Si substrate Dz zm • evaporated, short chain length, no relaxation, no interphase expected • E < 1 keV: surface effects • 1 keV < E < 4/6 keV: bulk Teflon • t3 AF2400 = 4 ns • “bulk”: t3 = 7 ns (M. Rudel) • E > 4/6 keV: implantation into Si • t3 remains constant • I3 decreases • Reference sample, no interphase!

  9. Teflon AF 2400, spin coated • Aim: • Comparison with evaporated Teflon • Observations: • Bulk value of t3 @ 2 keV • voltage ↑ t3 ↓ • Interpretation: • rearrangement of chains possible • dcoil < 20-100nm = thicknessinterphase < dfilm Remarks: Same polymer, thick oxide layer (not shown) • Clear influence of thick oxide layer on PALS, but not on interface width Similar results for other polymers, temperature dependence (Tg profiling) planned PALS suited to detect interphase width in thin films

  10. Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam (PLEPS @ NEPOMUC) Thin Films (SPP Polymer-solid interfaces and Interphases) evaporated and spin coated Teflon AF on Si-Wafer change of free volume due to solid substrate, (coiling changed?) Polymer Nanocomposites free volume as function of filler concentration, mixing rule and side effects Summary

  11. Polymer-nanocomposites Our task: free volume as a function of temperature for various filler concentrations Polymer: Nanoparticles: SiOx polyethylenpropylen PEP, (deuterated) Filler: Nanoparticles + Mw = 3000 g/mol (no entanglement) functionalized shell Ø 18 – 20 nm We know: system shows no change in dynamics at interphase (n-scattering) We expect: - free volume: ↑ - dynamics: either ↑ (more free volume) or ↓ (less mobility) S. Harms, K. Rätzke, F. Faupel, G. Schneider, L. Wöllner, D. Richter, Macromolecules, 43 (2010) 10505

  12. DSC, thermal analysis Pyris DSC Heating rate = 20 K/min Tg from onset Delta Cp from fit Results show clearly simple mixing

  13. Results: o-Ps lifetime = f(T, cfiller) 18% o-Ps lifetime ~ to hole size, mirrors macroscopic thermal expansion Systematic behavior with concentration and temperature observable => Tg, glass, rubbery = f (cfiller)

  14. Free volume and Intensity f (c) @ T = const. Observation: 3 @ -120 °C   c filler   local disturbance of packing? No, see n-scattering I3 = const  c filler   ?? Expected was decrease due to non-Ps forming nanoparticles Ansatz: positrons, randomly implanted, do not annihilate in nanoparticles diffuse out of nanoparticles and probe preferentially functionalized shell

  15. Microscopic thermal expansion and glass transition Observations: Tg cfiller  glassy = const rubbery   cfiller  Ansatz for explanation: Free volume is additive between functionalized shell and polymer No interphase needed for explanation

  16. Team, Cooperations & Sponsors cooperations: FRM II: PD Dr. C. Hugenschmidt, Dr. W. Egger nanocomposites: Dr. G. Schneider, Jülich and FRMII funding: DFG SPP 1369 BMBF Posimethod Prof. Dr. Franz Faupel Dipl.-Phys. Stephan Harms MSc. Tönjes Koschine MSc. Christian Ohrt

  17. Summary • PALS suitable method for investigation of free volume in polymers average lifetime measure for average free volume • TEFLON AF: distribution of free volume at polymer-solid interface no interphase for evaporated samples clear interphase for spin-coated samples • Polymer-nanocomposites nanocomposites without interphase show deviation from mixing rule • interphase should be differentiated from functionalized shell • positrons probe preferentially functionalized shell  3 

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