PPC 10 Smolenice 2011 Positron annihilation and free

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 1

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

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 3

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 4

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) 5

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 6

schematic of polymer-solid contact nanocomposite property { solid bulk value Interphase polymer z increased contribution from interphase char. length scale nm - µm key property: free volume 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 7

Teflon AF 2400 evaporated onto Si evaporated, short chain length, no relaxation, no interphase expected Dz Teflon AF 2400 Si substrate zm • E < 1 ke. V: surface effects • 1 ke. V < E < 4/6 ke. V: bulk Teflon 3 AF 2400 = 4 ns “bulk”: 3 = 7 ns (M. Rudel) • E > 4/6 ke. V: implantation into Si 3 remains constant I 3 decreases Reference sample, no interphase! 8

Teflon AF 2400, spin coated Aim: Comparison with evaporated Teflon Observations: • Bulk value of 3 @ 2 ke. V • voltage ↑ 3 ↓ Interpretation: • rearrangement of chains possible • dcoil < 20 -100 nm = 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 9

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 10

Polymer-nanocomposites Polymer: polyethylenpropylen PEP, (deuterated) = 3000 g/mol (no entanglement) Nanoparticles: Si. Ox Filler: Nanoparticles + functionalized shell Mw Ø 18 – 20 nm Our task: free volume as a function of temperature for various filler concentrations 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 11

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

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) 13

Free volume and Intensity f (c) @ T = const. Observation: 3 @ -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 14

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 15

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 16

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