Post on 20-Jan-2016
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: kr@tf.uni-kiel.de
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
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
7/17
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
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
11/17
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)
filler concentration (%)
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
)
filler concentration (%)
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)