volumes in Nano-scale Polymeric and Composite Membrane Systems Using Positron Annihilation Spectroscopy * Y.C. Jean 1,2 1 Department of Chemistry, University of Missouri-Kansas City 2 R&D Center for Membrane Technology and Department of Chemical Engineering, Chung- Yuan Christian University, Taiwan Collaborators: NIST:T. Nguyen, X. Gu; AIST: R. Suzuki, T. Ohdaira; CMT: J.I.Lai, Y.M. Sun, R. Lee, C.C. Hu *Supports: NSF and NIST, Ministry of Education (Taiwan)
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Y.C. Jean 1,2 1 Department of Chemistry, University of Missouri-Kansas City
Characterization of Free volumes in Nano-scale Polymeric and Composite Membrane Systems Using Positron Annihilation Spectroscopy *. Y.C. Jean 1,2 1 Department of Chemistry, University of Missouri-Kansas City - PowerPoint PPT Presentation
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Characterization of Free volumes in Nano-scale Polymeric and Composite Membrane Systems Using Positron
Annihilation Spectroscopy*
Y.C. Jean1,2
1Department of Chemistry, University of Missouri-Kansas City
2R&D Center for Membrane Technology and Department of Chemical Engineering, Chung-Yuan Christian
University, Taiwan Collaborators: NIST:T. Nguyen, X. Gu; AIST: R. Suzuki, T. Ohdaira; CMT: J.I.Lai, Y.M. Sun, R. Lee, C.C. Hu*Supports: NSF and NIST, Ministry of Education (Taiwan)
Outline
• Positron and Positronium Annihilation
• I. Positrons in Polymeric Nano-Scale Films
(1) Multi-Layer Structures
(2) Tg-depth dependence
• II. Polymeric Composite Membranes
(1) Surface layer structures
(2) Permeability and selectivity
The Positron
1930: Anti-electron (Positron) predicted by P.A.M. Dirac, Quantum Electrodynamics Theory.
1932: The Positron (positive electron), detected by C.D. Anderson in the cloud chamber from cosmic radiation.
1946: The Positronium atom (positron and electron bound state) detected by M. Deutch from positron annihilation in gases.
1960: Solid state physics: positron is localized in defects; positron is delocalized in lattices-Fermi surface.
1970: Nuclear medicine: positron emission tomography (PET)1975: Surface science: positron has a negative work function.1980-presence: Positron chemistry, material defect and surface tools.
Positron Annihilation Processes
1. When positron and electron meet, they can form Positronium (Ps). Positronium exists in two states, p-Ps (spins anti-aligned) and o-Ps (spins aligned): 2 photons (for p-Ps with 125 ps, or a few ns for pick-off with electrons with molecules) or 3 photon (for o-Ps 142 ns) produced by annihilation.
2. Positrons can freely annihilate with electrons without forming Ps with lifetime ~10-9 s to ∞ (in UHV 10-11 torr, live one hour).
3. The Feynman diagram shows that the annihilation distance starts 10-12.5 m (Δx~ħ/mc) and the time 10-21 s (t~ħ/mc2)-delta function and sudden approximation.
4. Annihilation characteristics depend on electron properties of matter.
Positron Annihilation Spectroscopy (PAS)
PAS monitors annihilation γ-rays properties, which are related to materials and electronic properties of systems studied. Four experimental techniques are currently used in PAS:
1. Positron annihilation lifetime spectroscopy (PAL): atomic and molecular free volumes and holes in polymers, solids.
2. Doppler broadening of annihilation energy spectroscopy (DBES): atomic defects in semiconductors, polymers.
3. Angular correlation of annihilation radiation (ACAR): Anisotropy structures of free volumes, defects, Fermi surface.
4. Variable mono-energetic positron beam: surface and interfaces.
PAS contains the most fundamental properties of molecules (chemistry):
wave function and electron density
• PAL measure positron annihilation lifetime τ:
τ= n |xyz n(x,y,z)* +(x,y,z) dxdydz |2
• DBES measures electrons’ momentum distributions at the longitudinal direction (z):
N(pz)=n pxpy |xy zn(r)* +(r) e-iP•r d r|2 dpxdpy
• 2D-ACAR measures electrons’ momentum distribution at the transverse directions (x,y):
N(px, py)=n pz|xy zn(r)* +(r) e-iP•r d r|2 dpz
Localization of positron and Ps
The Decay Scheme of 22Na
10Ne22
3 ps
0+
2+
E2
1.2746 EC 10%
+ 0.05%
+ 90%
+, EC
3+ 2.60 y
11Na22
0.511 MeV0.511 MeV
180 o
(e-e+)
-
Two-photon Annihilation of a Positron-Electron Annihilation Pair
Calibrated defect radius(Å)
0 i
EE i
)E(N
)E(NS
2
1
N(E
)
E( keV)
Low momentum (S-parameter)
E2E
1 511
S is a measure of defect property:
(1) Large hole Large Sp•x /2
(2) Large defect concentration large S
Doppler broadening S parameter
Positron Annihilation Lifetime
0 5 10 15 20 25
10
100
1000
10000
100000
ç3=1.8 ns
ç2=0.45 ns
ç1=0.125 ns
Cou
nts
Time (ns)
)BAI(Vf
)R
R2sin
2
1
R
R1(
2
1
3fv
1
003
tλii ieλIN(t)
Res
olve
d D
efec
t Siz
e
1 cm
1000
100
10
1
1000
100
10
1Å
OM
TEM X-ray Scattering
Positron Spectroscopy
1 Å 10 100 1000 1 10 100 1000
Depth
Mech
Def
ect C
once
ntra
tion
(pp
m)
10
OM TEM
X-ray Scattering
Positron Spectroscopy
1Å 10 100 1000 1 10 100 1000
Depth
Mech1%
1000
100
1 ppm
STM/AFM
STM/AFM
PAS can resolve size, concentration and distribution of atomic
scale defects
Comparison of PAS and other techniques
A sow positron beam (0- 30 keV) for depth profile (0-10 µm) of free volume
22Na e+ source 50mCi
Moderator
ExB e+ filter
Lifetime detector attachment
Sample chamber
S.S. Detector
Data acquisition system
Accelerator 0- 30kV
Magnetic coils 75G
Depth and dispersion of depth
6.10
400)( EEZ
Free-volume Concept in Macromolecules (polymers)
Free volume is the free moving (very fast, ps-ns) open space (very small, sub-nm) inside a molecule or system.
A simple expression of the free volume (Vf) can be written as the total volume (Vt) minus the “occupied volume” (V0):
Vf = Vt – V0
The existence of free volume (1-10%) makes polymers as the most widely used materials in our human life today.
Polymer film
Substrate
Diagram Of Nano-scale Polymeric Film On Substrate
1. Free-volume S-parameter for different thickness of polystyrene films on Si
2. Less relationship between S (transition) and selectivity
0 1000 2000 3000 4000 5000 6000 70001000
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
Flux Water concentration
Thickness of the second layer (nm)
Flu
x (
g/m
2h
)
95
96
97
98
99
100
Wa
ter
co
nc
en
tra
tio
n in
pe
rme
ate
(w
t%)
0.477 0.478 0.479 0.480 0.4811000
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
Flux Water concentration
S parameter in the second layer, S2
Flu
x (g
/m2
h)
95
96
97
98
99
100
Wat
er c
on
cen
trat
ion
in p
erm
eate
(w
t%)
Temperature of TETA doping (25, 50, 70 o)Temperature increases PA thickness
0 5 10 15 20 25 300.44
0.45
0.46
0.47
0.48
0.49
7.365.123.221.660.54
Mean depth (m)
0
Doped 10 min:
PATFC021 : 25oC
PATFC025 : 50oC
PATFC003 : 70oC
S p
aram
eter
Positron incident energy (keV)
20 25 30 35 40 45 50 55 60 65 70 75
0.46
0.47
0.48
0.49
0.50
0.51
0.52
0
50
100
150
200
250
300
350
400
S parameter
S p
aram
eter
Temperature (oC)
Thi
ckne
ss (
nm)
Layer 1
Thickness
20 25 30 35 40 45 50 55 60 65 70 750.475
0.476
0.477
0.478
0.479
0.480
0.481
0.482
0
500
1000
1500
2000
2500
3000
3500
4000
S parameter
S p
ara
me
ter
Temperature (oC)
Th
ickn
ess
(n
m)
Layer 2
Thickness
Temp increases both layer 1 and layer 2 thickness but decreases free-volume S parameters
PA layer (1) correlations
0.46 0.47 0.48 0.49 0.50 0.51 0.52600
800
1000
1200
1400
1600
1800
2000
40
60
80
100
Flux
Flu
x (g
/m2 hr
)
S parameter (Layer 1)
Wa
ter
Co
ncen
trat
ion
(wt%
)
Water concentration
0 100 200 300 400500
1000
1500
2000
40
60
80
100
Flu
x (g
/m2 h
r)
Thickness L1 (nm)
Wa
ter
Co
nce
ntr
atio
n in
pe
rme
ate
(w
t%)
Flux
Water concentration
1. Flux (permeability) and S1 free-volume parameter follows D=A exp(-B/ffv)
2. Selectivity decreases as S1 and PA thickness increases
Transition layer (2) correlations
1. Flux (permeability) and S2 free-volume parameter follows D=A exp(-B/ffv)
2. Selectivity decreases as S2 and PA thickness increases
0.476 0.477 0.478 0.479 0.480600
800
1000
1200
1400
1600
1800
2000
40
60
80
100
Flux
Flu
x (g
/m2h
r)
S parameter (Layer 1)
Wa
ter
Co
nce
ntr
atio
n in
pe
rme
ate
(wt%
)
Water concentration
1. A 3-layer structure of the PAN membranes is determined: (1) Skin m-PAN (300-400 nm); (2) Transition larer from dense to porous PAN (2 µm)(3) Porous m-PAN
2. A 3-layer polyamide thin-film composite PAN membrane is(1) polyamide layer: a very near surface layer (50-300 nm)(2) Transition layer from dense to porous m-PAN (0.5-4 µm)(3) Porous m-PAN layer
3. Correlation between free volume S parameter and flux in the free-volume theory: Flux=A(-B/S)
4. Selectivity is mainly controlled by thickness of skin polyamide layer, and secondary affected by the transition layer.
5. Effect of free volume size and selectivity can be investigated using PAS
6. Future applications of PAS to membrane technology for RO and NF are promising.
II. Conclusions based on PA/m-PAN of pervaporation of membrane separation
Summary
I. Nano-scale polymeric films:(1) Depth and interfacial structures for layers and nano-
composite systems.(2) Tg-depth dependence of polymeric systems on
different substrates with different interfacial interactions and UV irradiations.
II. Membranes and coatings:(1) Free-volume depth profile of membranes and
coatings(2) Early detection of polymeric degradations.(3) Effects of free volume size and struture on
membrane performances (permeselectivities)
Jack Liu, Lakshmi Chakka, Dr. Jean, Dr.Hongmin Chen, Wassen