Application of RHC
to Nanostructured Polymer Systems
Guy Van Assche, Jun Zhao, Nicolaas-Alexander Gotzen,
Nick Watzeels, Hans E. Miltner, Bruno Van Mele
Vrije Universiteit Brussel (VUB)
Research Unit for Physical Chemistry and Polymer Science
Department Materials and Chemistry
Faculty of Engineering
with the support of TA Instruments, FWO-Vlaanderen, Universiteit Hasselt
NATAS 2009Sept 20-23, 2009, Lubbock, Texas, USA
2
Outline
• Introduction RHC
• Results and discussion– Polymer-fullerene blends for solar cells– Crystallization kinetics of PCL nanocomposites– Crystallization and melting in iPP nanocomposites
• Conclusions
3
Introduction RHC
• Project RHC– Introduced at the 2007 NATAS meeting– Design, fabrication and subsequent evaluation of rapid-scanning DSC technology– For operation at high scanning rates, up to 2000 K/min in heating, similar in cooling– Retain ease of use and sample preparation of conventional DSC
→ DSC with Tzero™ technology but about 10x smaller ; heating by light (TGA Q5000)
– Four beta units were manufactured and delivered in june and november 2008
4
Introduction RHC
5
Introduction RHC – Performance and calibration
• Performance– Heat at 1500 K/min to 225°C– Cool at 1000 K/min to 75°C
– Switch to Neon for faster heating
• Calibration– Tzero™ calibration
• Empty furnace + Sapphire
– Indium– Calibrate at desired rate
• Shift ca. 2.5°C at 1000 K/min
-2000
-1000
0
1000
2000
Der
iv. T
zero
Tem
pera
ture
(°C
/min
)
-200 -100 0 100 200 300 400Temperature (°C)
HeatingProfileNeon.001––––––– CoolingProfileHelium.001––––––– HeatingProfileHelium.002–––––––
Universal V4.1D TA Instruments
10 K/min
20 K/min
50 K/min
100 K/min
500 K/min
200 K/min
1000 K/min
-80
-60
-40
-20
0
He
at F
low
T4
P (
W/g
)
140 150 160 170 180 190Temperature (°C)Exo Up Universal V4.1D TA Instruments
156.0
157.0
158.0
159.0
0 500 1000
Heating rate in K/min
Te
mp
era
ture
in °
C
6
Introduction RHC – Performance and calibration
• Performance– Heat at 1500 K/min to 225°C– Cool at 1000 K/min to 75°C
– Switch to Neon for faster heating
• Calibration– Tzero™ calibration
• Empty furnace + Sapphire
– Indium– Calibrate at desired rate
– Verification four samples• 156.60 °C ± 0.13 °C
• 28.93 J/g ± 0.21 J/g
158.37°C
156.53°C29.19J/g
158.23°C
156.50°C28.89J/g
158.72°C
156.78°C28.68J/g
158.40°C
156.58°C28.97J/g
-60
-40
-20
0
20
Hea
t Flo
w T
4P (
W/g
)
130 140 150 160 170 180 190Temperature (°C)Exo Up Universal V4.1D TA Instruments
-2000
-1000
0
1000
2000
Der
iv. T
zero
Tem
pera
ture
(°C
/min
)
-200 -100 0 100 200 300 400Temperature (°C)
HeatingProfileNeon.001––––––– CoolingProfileHelium.001––––––– HeatingProfileHelium.002–––––––
Universal V4.1D TA Instruments
7
Outline
• Introduction RHC
• Results and discussion– Polymer-fullerene blends for solar cells– Crystallization kinetics of PCL nanocomposites– Crystallization and melting in iPP nanocomposites
• Conclusions
8
Polymer-fullerene blends for solar cells
• Bulk heterojunction solar cellsDonor: conducting polymer
Acceptor: fullerene
Photovoltaic process:Photon absorption → exciton generation
Diffusion to interface → exciton dissociation
Generated + and – charges flow to electrodes
Need co-continuous phase separated morphology
with ca. 10 nm dimension
Sn
O
O n
P3HT MDMO-PPV
PCBM
Sariciftci NS, Smilowitz L, Heeger AJ, Wudl F, Science, 1992, 258, 1474
Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ, Science, 1995, 270, 1789
9
Polymer-fullerene blends for solar cells - Aim
• Bulk heterojunction solar cellsDonor: conducting polymer
Acceptor: fullerene
Co-continuous phase separated morphology
with ca. 10 nm dimension
MDMO-PPV / PCBM at 110°C:Growth crystalline PCBM domains
Reduction efficiency within hours
Study phase formation processes
and state diagram to understand
morphology formation and stability
S. Bertho et al., Solar Energy Materials & Solar Cells 92 (2008) 753–760
O
O n
MDMO-PPV PCBM
1:4
110°C
2 µm
10
Polymer-fullerene blends for solar cells - Materials
• MaterialsDonor: P3HT (Merck)
MDMO-PPV (Merck)
High Tg-PPV (Merck)
Acceptor: PCBM (Solenne)
Blends drop-cast from chlorobenzene
• InstrumentsTA Instruments Q2000 Tzero DSC with MDSC option
DSC: 5 mg, 10 K/min
heat-cool-heat
MTDSC: 5 mg, 2.5 K/min, modulation 0.5 K / 60 s
heat-quench-heat
TA Instruments RHC
DSC: 0.5 mg, 500 K/min
heat-cool-heat
Calibration: T-zero calibration with sapphire, Indium for T and HF
SP3HT
n
O
OMDMO-PPV
n
O
O
PCBM
OR'
OC10
OMe
OC10ORRO
x y z
n
High Tg-PPV
11
Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMDSC results
• MDMO-PPV / PCBMMDMO-PPV:amorphous Tg ca. 25 - 50°C
PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C
Crystallisation retarded in presence of MDMO-PPV
Formation nano-morphology by crystallization PCBM + …
To stabilise nano-morphology, a glassy amorphous phase is desirable.
Tg of amorphous phase in blends? Tg of amorphous PCBM?
1st cooling 2nd heating
MDMO-PPVTg
CrystallisationPCBM
Tg MDMO-PPV
MeltingPCBM
12
Polymer-fullerene blends for solar cells – pure PCBMMTDSC and RHC results
• Pure PCBMRHC: Nearly completely amorphous, Tg ca. 130°C,
start cold-crystallization near 225°C, Tm ca. 280°C
MTDSC: not fully amorphous after in situ quench (avoid oxid. degradation), Tg ca. 130°C
Tg PCBM > Tg MDMO-PPV → Crystallization PCBM → Tg remaining amorphous phase ↓
Measure Tg of in situ quenched amorphous homogeneous blends in RHC
RHC: 2nd heating at 500 K/minafter in situ quench PCBM
Cold-cryst.
Melting
Tg
Cold-cryst.
PCBM
MTDSC: 2nd heating at 2.5 K/minafter in situ quench
MeltingTg
Cp
13
Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMMTDSC and RHC results
• MDMO-PPV:PCBM 1:4 or 80 wt% PCBMRHC: 2 Tg’s phase separated in liquid state
MTDSC: indications for 2 Tg’s, S/N worse
At 70-90 wt% PCBM double Tg is observed using RHC
→ Indication for phase separation in liquid state
→ Explains coarser, micrometer-sized morphologies found in this region
-100 0 100 200 300
1.5
2.0
2.5
3.0
3.5
50 100 150
0.002
0.004
0.006
Double Tg
Figure 14a MTDSC: 2nd (heating after quench),
2.5 K min-1, +/- 0.5 K per 60 s
App
aren
t sp
ecifi
c he
at c
apac
ity, c
papp (
J g-1
K-1)
Temperature, T (oC)
MDMO-PPV/PCBM
fw
PCBM, wt % 80.1
MTDSC: 2nd heating at 2.5 K/min
Cp
dCp/dT
RHC: 2nd heating at 500 K/minderiv.
14
Polymer-fullerene blends for solar cells – State diagrams
• Phase separation in liquid state:
- MDMO-PPV, High-Tg-PPV: Phase separate between 70 wt% and 90 wt% PCBM
- P3HT: Single Tg for each composition
• Long-term stability: compare Tg and max. operation temperature 80 °C
In range of optimal solar cell efficiency (50 wt% and 80 wt% PCBM)
– P3HT and MDMO-PPV have Tg < 80 °C → poor long-term stability
– High-Tg-PPV has Tg slightly above 80 °C → expect better stability
Tg’s + melting and crystallizationGlass transitions
15
Isothermal crystallization kinetics of PCL nanocomposites
• Introduction RHC
• Results and discussion– Polymer-fullerene blends for solar cells– Crystallization kinetics of PCL nanocomposites– Crystallization and melting in iPP nanocomposites
• Conclusions
16
Isothermal crystallization kinetics of PCL nanocomposites
• Nanocomposites– Poly(ε-caprolactone) (PCL): CAPA6500
• Tg = -65 °C, Tm = 60 °C
– Carbon nanotubes: Nanocyl 7000 MWCNT– Nanocomposites by extrusion
Debundling confirmed by rheometry and SEM
Study isothermal crystallization kinetics of PCL-based nanocompositesfor modelling the solidification extruded sheets
Mettler 821 DSC
DSC: 5 mg, cooling to Tiso at 50 K/min, calibrated at 10 K/min
TA Instruments RHC
DSC: ca. 0.5 mg, cooling to Tiso at 500 K/min, calibrated at 100 K/min
Calibration: T-zero calibration with sapphire, Indium for T and HFMeasurement: compensation on reference with Al
nO
O
17
Isothermal crystallization kinetics - PCL
-60
-40
-20
0
20
40
60
80
0 1 2 3 4 5 6 7
Time (min)
He
at
flo
w (
W/g
)
-150
-100
-50
0
50
100
150
Te
mp
era
ture
(°C
)• Temperature program:
– Stay isothermal at 70°C for 2 min, cooled down at 500 K/min to T iso
• Compensation: to reduce overshoot in heat flow– ca. 0.8 mg of aluminum in reference crucible– Heat flow overshoot measured at 60 °C – no crystallization– Overshoot ca. 0.2 W/g, to baseline level in ca. 0.5 min
-1.0
0.0
1.0
2.0
2.45 2.95 3.45 3.95 4.45 4.95
Time (min)
He
at
flo
w (
W/g
)
30 °C60 °C
18
Isothermal crystallization kinetics - PCL
• Crystallization kinetics:– Studied by RHC from 38 °C to 16°C– For crystallization taking less than 0.5 min
→ transient from scan-to-isothermal begins to interfere
→ at 16 °C maximum not reliable.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 1.0 2.0 3.0 4.0 5.0
Time (min)
He
at
flo
w (
W/g
)
26 °C
30 °C
38 °C
34 °C
0
2
4
6
8
10
12
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (min)
He
at
flo
w (
W/g
)
16 °C
20 °C
24 °C
19
Isothermal crystallization kinetics - PCL
• Crystallization kinetics:– Studied by RHC from 38 °C to 16°C– For crystallization taking less than 0.5 min
→ transient from scan-to-isothermal begins to interfere
→ at 16 °C maximum not reliable– 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 1.0 2.0 3.0 4.0 5.0
Time (min)
He
at
flo
w (
W/g
)
26 °C
30 °C
38 °C
34 °C
0
2
4
6
8
10
12
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (min)
He
at
flo
w (
W/g
)
16 °C
20 °C
24 °C
20
-5.0
-4.0
-3.0
-2.0
-1.0
0.2 0.4 0.6 0.8 1.0
Reduced temperature (-)
log
(v
(1
/s))
nucleationdiffusion
• Hoffman-LauritzeExpression for crystal growth rate
diffusion nucleation
Isothermal crystallization kinetics - PCL
• Crystallization kinetics:– Studied by RHC from 38 °C to 16°C– For crystallization taking less than 0.5 min
→ transient from scan-to-isothermal begins to interfere
→ at 16 °C maximum not reliable– 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation
– DSC + RHC: range of close to 3 orders of magnitude
*
exp exp go
c c
KUG G
R T T T Tf
RHC
DSC
21
Isothermal crystallization kinetics – PCL + Carbon Nanotubes
0.0
0.5
1.0
1.5
2.0
2.5
0.0 1.0 2.0 3.0 4.0 5.0
Time (min)
He
at
flo
w (
W/g
)
48 °C
50 °C
52 °C
51 °C
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (min)
He
at
flo
w (
W/g
)
44 °C
45 °C
47 °C
46 °C
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 1.0 2.0 3.0 4.0 5.0
Time (min)
He
at
flo
w (
W/g
)
26 °C
30 °C
38 °C
34 °C
0
2
4
6
8
10
12
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (min)
He
at
flo
w (
W/g
)
16 °C
20 °C
24 °C
PCL + CNT PCL + CNT
PCL PCL
22
Isothermal crystallization kinetics - PCL + Carbon Nanotubes
• Influence carbon nanotubes:– Strong nucleating effect of CNT– Similar rates of crystallization as
pure PCL at 15 – 25 °C higher temperatures
or,
At same temperature ca. 300x faster
0.0
0.5
1.0
1.5
2.0
2.5
0.0 1.0 2.0 3.0 4.0 5.0
Time (min)
He
at
flo
w (
W/g
)
48 °C
50 °C
52 °C
51 °C
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (min)
He
at
flo
w (
W/g
)
44 °C
45 °C
47 °C
46 °C
-5.0
-4.0
-3.0
-2.0
-1.0
0.2 0.4 0.6 0.8 1.0
Reduced temperature (-)
log
(v
(1
/s))
23
Crystallization and melting in iPP-nanocomposites
• Introduction RHC
• Results and discussion– Polymer-fullerene blends for solar cells– Crystallization kinetics of PCL nanocomposites– Crystallization and melting in iPP nanocomposites
• Conclusions
24
Crystallization and melting in iPP-nanocomposites
• Crystallization of iPP and iPP+CNT– CNT act as nucleating agent
→ iPP + CNT crystallizes at T+15 °C
→ Expect iPP + CNT melt at higher T
- XRD: iPP w/o CNT: α—phase
- Melting of iPP and iPP+CNT– Heating of in situ quenched samples
– At conventional low rate: iPP melts at higher T than iPP +
CNT ???
– Cause:
During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β
– At high rate: iPP melts at lower T (ok)
CNT result in structure that hinders recrystallization for iPP+CNT
Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762
Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085
iPP + CNT
iPP
25
Crystallization and melting in iPP-nanocomposites
• Crystallization of iPP and iPP+CNT– CNT act as nucleating agent
→ iPP + CNT crystallizes at T+15 °C
→ Expect iPP + CNT melt at higher T
- XRD: iPP w/o CNT: α—phase
- Melting of iPP and iPP+CNT– Heating of in situ quenched samples
– At conventional low rate: iPP melts at higher T than iPP +
CNT ???
– Cause:
During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β
– At high rate: iPP melts at lower T (ok)
CNT strongly nucleate PCL, creating a transcrystalline structure that hinders recrystallization into the β-phase
Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762
Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085
TEM: Transcrystalline interphase around CNTJ. Loos (TU Eindhoven, The Netherlands)
Sketch for possible nucleation mechanism
26
• Phase behavior of photovoltaic blends– RHC: Faster in situ quenching – important if oxidative degradation occurs in melt
– Glass transition of amorphous PCBM
– Double glass transitions in some blends indicate phase separation in melt
• Isothermal crystallization in PCL and its nanocomposites– RHC: Faster cooling and faster response
– Processes that take 30 s or more can be studied
– Extension of temperature range that can be studied, further extension by chip calorimetry and microcalorimetry
• Crystallization and melting in iPP and its nanocomposites– RHC: Cooling and heating at higher rates can suppress (slower) kinetic events
– Recrystallization of iPP is hindered in presence of CNT, formation of a transcrystalline interphase
• FWO-Vlaanderen (Belgium), TA Instruments (Delaware, USA) and OZR-VUB are acknowledged for their support
Conclusions
27
Thank you
28
Polymer-fullerene blends for solar cells – P3HT / PCBMDSC results
• P3HT / PCBMP3HT: semi-crystalline Tg ca. 0 - 25°C, Tm ca. 210°C, Tc ca. 180°C
PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C
For both P3HT and PCBM, crystallisation retarded in presence of second component
Formation nano-morphology by dual crystallization
1st cooling 2nd heating
P3HTTg
CrystallisationPCBM
P3HTTg Melting
MeltingPCBM
Crystallization
29
Polymer-fullerene blends for solar cells – pure PCBMMTDSC on sample aged at 103°C for 4000 min
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