1/17 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, Kiel, Germany

2/17 Polymeric Materials, Free Volume fuel cell driven submarine Yacht during kiel week color map: carbon oxygen nitrogen hydrogen fluorine Free volume, important for diffusion, viscosity, adhesion barnacles

3/17 Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam 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

4/17 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 I 3  positronium formation probability * concentration of free volume Moderated pulsed positron beam  depth resolution possible

5/17 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)

6/17 Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam 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

7/17 schematic of polymer-solid contact z char. length scale nm - µm nanocomposite increased contribution from interphase property bulk value polymersolid Inter- phase { key property: free volume Here: Free volume of Teflon AF 2400 as a function of distance to interface SPP 1369 interfaces and Interphases controlled preparation property profiling modeling and simulation S. Harms, K. Rätzke, V. Zaporojtchenko, F. Faupel, W. Egger, L. Ravelli, Polymer, 52 (2011) 505

8/17 Teflon AF 2400 evaporated onto Si evaporated, short chain length, no relaxation, no interphase expected E < 1 keV: surface effects 1 keV < E < 4/6 keV: bulk Teflon  3 AF2400 = 4 ns “bulk”:  3 = 7 ns (M. Rudel) E > 4/6 keV: implantation into Si  3 remains constant I 3 decreases Reference sample, no interphase! Si substrate zmzm zz Teflon AF 2400

9/17 Teflon AF 2400, spin coated Aim: Comparison with evaporated Teflon Observations: Bulk value of  2 keV voltage ↑   3 ↓ Interpretation: rearrangement of chains possible d coil < nm = thickness interphase < d film 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 (T g profiling) planned PALS suited to detect interphase width in thin films

10/17 Outline Motivation Polymeric materials, free volume, interphases and interfaces Free volume / Positron annihilation lifetime spectroscopy Principle, conversion lifetime - volume size, experimental setup positron beam 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

11/17 Polymer-nanocomposites Our task: free volume as a function of temperature for various filler concentrations Polymer: Nanoparticles: SiO x polyethylenpropylen PEP, (deuterated) Filler: Nanoparticles + M w = 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

12/17 DSC, thermal analysis Pyris DSC Heating rate = 20 K/min Tg from onset Delta Cp from fit Results show clearly simple mixing

13/17 Results: o-Ps lifetime = f(T, c filler ) o-Ps lifetime ~ to hole size, mirrors macroscopic thermal expansion Systematic behavior with concentration and temperature observable => T g,  glass,  rubbery = f (c filler ) 18%

14/17 Free volume and Intensity f T = const. Observation:  -120 °C   c filler   local disturbance of packing? No, see n-scattering I 3 = 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

15/17 Microscopic thermal expansion and glass transition Observations: T g  c filler   glassy = const  rubbery   c filler  Ansatz for explanation: Free volume is additive between functionalized shell and polymer No interphase needed for explanation

16/17 Team, Cooperations & Sponsors Prof. Dr. Franz Faupel MSc. Christian Ohrt Dipl.-Phys. Stephan Harms cooperations: FRM II:PD Dr. C. Hugenschmidt, Dr. W. Egger nanocomposites:Dr. G. Schneider, Jülich and FRMII MSc. Tönjes Koschine funding: DFG SPP 1369 BMBF Posimethod

17/17 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3