1/17 PPC 10, Smolenice 2011 Positron annihilation and free volume in polymer-solid interfaces and in...

1/17

PPC 10, Smolenice 2011

Positron annihilation and free volume in polymer-solid interfaces and in nanocomposites

Klaus Rätzke, Stephan Harms, Franz FaupelTechnische Fakultät der Universität Kiel,

Institut für Materiawissenschaft - MaterialverbundeKaiserstr. 2, 24143 Kiel, Germany

e-mail: [email protected]

2/17

Polymeric Materials, Free Volume

fuel cell driven submarine

Yacht during kiel week

color map:carbonoxygennitrogenhydrogenfluorine

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 (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

4/17

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 I3 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)

0.5 mz z

1.711m

p

z E

median implantation depth:

FWHM:

J. Algers, P. Sperr, W. Egger, G. Kögel, F. MaurerPhys. Rev. B (2003)0 2 4 6 8 10 12 14 16 18

0 53 172 344 562 824 1125 1464 1840 2250

0.0

0.5

1.0

z

P_1KEV P_5KEV P_10KEV

E (keV)

zm (nm) ~ E1.71

zm P

(z, E

)

6/17

Outline

Motivation










Summary

7/17

schematic of polymer-solid contact

z

char. length scale nm - µm

nanocomposite

increased contributionfrom interphase

property

bulk valuepolymersolid

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

I3 decreases

Reference sample, no interphase!

0 2 4 6 8 10 12 14 16 180

5

10

15

E (keV)

I 3 (%

)

I3 - calculation

I3 - exp. data

Si substrate

zm

z

TeflonAF 2400

0 2 4 6 8 10 12 14 16 18

0 53 172 344 562 824 1125 1464 1840 2250

0.0

0.5

1.0

P(E=1ekV) P(E=5ekV) P(E=10ekV)

E (keV)

zm (nm) ~ E1.71

P(z

, E

)

0 4 8 120

4

8

12

16

20

24

0

1

2

3

4

5

I 3 (%

)

33 mm 360 nm 717 nm

E (keV)

3 (n

s)

9/17

0 2 4 6 8 10 12 140

1

2

3

4

5

6

7

0

5

10

15

20

25

30 220 nm 160 nm 110 nm 65 nm

3 (n

s)

E (keV)

I 3 (%

)

Teflon AF 2400, spin coated

Aim:

Comparison with evaporated Teflon

Observations:

• Bulk value of 3 @ 2 keV

• voltage ↑ 3 ↓

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) plannedPALS suited to detect interphase width in thin films

0 2 4 6 8 10 12 14 16 180

1

2

3

4

5

6

7

0

4

8

12

16

20

24

28

3 (n

s)

E (keV)

TeflonAF spin coatedd = 220 nm

I 3 (%

)

10/17

Outline

Motivation










Summary

11/17

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

12/17

DSC, thermal analysis

0 10 20 30 40 50 60-75

-70

-65

-60

0.0

0.2

0.4

0.6

0.8

1.0

Tg DSC

cp

Tg D

SC (°C

)

filler concentration (%)

cp

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, cfiller)

-120 -80 -40 01.0

1.5

2.0

2.5

3.0

cfiller 0

6 18 35 60 100

3 (n

s)

T (°C)

-150 -100 -50 0 500.0

0.5

1.0

1.5

2.0

2.5

3.0

0

10

20

30

40

50

60

70

g

15% Lifetime3 Dispers.3 Intensity3

3 (n

s)

T (°C)

r

Tg

I 3 (%

)o-Ps lifetime ~ to hole size, mirrors macroscopic thermal expansion

Systematic behavior with concentration and temperature observable

=> Tg, glass, rubbery = f (cfiller)

18%

14/17

Free volume and Intensity f (c) @ T = const.

0 20 40 60 80 100

1.5

2.0

2.5

0

10

20

30

t3 @ -120°C from fit T < T

g PALS

I3 mean

@ 0°C T 30°C

3 (n

s)


I 3 (%

)

-120 -80 -40 01.0

1.5

2.0

2.5

3.0

cfiller 0

6 18 35 60 100

3 (n

s)

T (°C)

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

15/17

Microscopic thermal expansion and glass transition

0 20 40 60 80 1000.000

0.005

0.010

0.015

0.020

0.025

0.030

hg

hr

hfiller concentration (%)

0 20 40 60 80 100

-110

-100

-90

-80

-70

-60

-50

Tg PALS

Tg P

ALS (°C

)


Tg filler

Tg PEP

-120 -80 -40 01.0

1.5

2.0

2.5

3.0

cfiller 0

6 18 35 60 100

3 (n

s)

T (°C)

Observations:

Tg cfiller

glassy = const

rubbery cfiller

Ansatz for explanation:

Free volume is additive between functionalized shell and polymer

No interphase needed for explanation

16/17

Team, Cooperations & Sponsors

Prof. Dr. Franz Faupel

MSc. Christian OhrtDipl.-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 polymersaverage lifetime measure for average free volume

• TEFLON AF: distribution of free volume at polymer-solid interfaceno interphase for evaporated samplesclear 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

0 2 4 6 8 10 12 14 16 180

1

2

3

4

5

6

7

0

4

8

12

16

20

24

28

3 (n

s)

E (keV)

TeflonAF spin coatedd = 220 nm

I 3 (%

)

0 4 8 120

4

8

12

16

20

24

0

1

2

3

4

5

I 3 (%

)

33 mm 360 nm 717 nm

E (keV)

3 (n

s)

-120 -80 -40 01.0

1.5

2.0

2.5

3.0

cfiller 0

6 18 35 60 100

3 (n

s)T (°C)

1/17 PPC 10, Smolenice 2011 Positron annihilation and free volume in polymer-solid interfaces and in...

Documents

Transcript of 1/17 PPC 10, Smolenice 2011 Positron annihilation and free volume in polymer-solid interfaces and in...