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Application of RHC to Nanostructured Polymer Systems Guy Van Assche, Jun Zhao, Nicolaas-Alexander Gotzen, Nick Watzeels, Hans E. Miltner, Bruno Van Mele.

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Presentation on theme: "Application of RHC to Nanostructured Polymer Systems Guy Van Assche, Jun Zhao, Nicolaas-Alexander Gotzen, Nick Watzeels, Hans E. Miltner, Bruno Van Mele."— Presentation transcript:

1 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 2009 Sept 20-23, 2009, Lubbock, Texas, USA

2 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 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 4 Introduction RHC

5 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

6 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 °C ± 0.13 °C J/g ± 0.21 J/g

7 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 8 Polymer-fullerene blends for solar cells Bulk heterojunction solar cells Donor: 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 P3HTMDMO-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 9 Polymer-fullerene blends for solar cells - Aim Bulk heterojunction solar cells Donor: 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 MDMO-PPVPCBM 1:4 110°C 2 µm

10 10 Polymer-fullerene blends for solar cells - Materials Materials Donor:P3HT (Merck) MDMO-PPV (Merck) High T g -PPV (Merck) Acceptor:PCBM (Solenne) Blends drop-cast from chlorobenzene Instruments TA 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

11 11 Polymer-fullerene blends for solar cells – MDMO-PPV / PCBM DSC results MDMO-PPV / PCBM MDMO-PPV:amorphousT g ca °C PCBM:semi-crystallineT m ca. 280°C, T c 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. T g of amorphous phase in blends? T g of amorphous PCBM? 1 st cooling 2 nd heating MDMO-PPV T g Crystallisation PCBM T g MDMO-PPV Melting PCBM

12 12 Polymer-fullerene blends for solar cells – pure PCBM MTDSC and RHC results Pure PCBM RHC:Nearly completely amorphous, T g ca. 130°C, start cold-crystallization near 225°C, T m ca. 280°C MTDSC:not fully amorphous after in situ quench (avoid oxid. degradation), T g ca. 130°C T g PCBM > T g MDMO-PPV → Crystallization PCBM → T g remaining amorphous phase ↓ Measure T g of in situ quenched amorphous homogeneous blends in RHC RHC: 2 nd heating at 500 K/min after in situ quench PCBM Cold-cryst. Melting TgTg Cold-cryst. PCBM MTDSC: 2 nd heating at 2.5 K/min after in situ quench Melting TgTg CpCp

13 13 Polymer-fullerene blends for solar cells – MDMO-PPV / PCBM MTDSC and RHC results MDMO-PPV:PCBM 1:4 or 80 wt% PCBM RHC:2 T g ’s  phase separated in liquid state MTDSC:indications for 2 T g ’s, S/N worse At wt% PCBM double T g is observed using RHC → Indication for phase separation in liquid state → Explains coarser, micrometer-sized morphologies found in this region MTDSC: 2 nd heating at 2.5 K/min CpCp dC p /dT RHC: 2 nd heating at 500 K/min deriv.

14 14 Polymer-fullerene blends for solar cells – State diagrams Phase separation in liquid state: - MDMO-PPV, High-T g -PPV: Phase separate between 70 wt% and 90 wt% PCBM - P3HT: Single T g for each composition Long-term stability: compare T g and max. operation temperature 80 °C In range of optimal solar cell efficiency (50 wt% and 80 wt% PCBM) –P3HT and MDMO-PPV have T g < 80 °C → poor long-term stability –High-T g -PPV has T g slightly above 80 °C → expect better stability T g’s + melting and crystallization Glass transitions

15 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 16 Isothermal crystallization kinetics of PCL nanocomposites Nanocomposites –Poly(ε-caprolactone) (PCL): CAPA6500 T g = -65 °C, T m = 60 °C –Carbon nanotubes: Nanocyl 7000 MWCNT –Nanocomposites by extrusion Debundling confirmed by rheometry and SEM Study isothermal crystallization kinetics of PCL-based nanocomposites for modelling the solidification extruded sheets Mettler 821 DSC DSC:5 mg, cooling to T iso at 50 K/min, calibrated at 10 K/min TA Instruments RHC DSC:ca. 0.5 mg, cooling to T iso at 500 K/min, calibrated at 100 K/min Calibration: T-zero calibration with sapphire, Indium for T and HF Measurement: compensation on reference with Al

17 17 Isothermal crystallization kinetics - PCL 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

18 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.

19 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

20 20 nucleationdiffusion Hoffman-Lauritze Expression 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 RHC DSC

21 21 Isothermal crystallization kinetics – PCL + Carbon Nanotubes PCL + CNT PCL

22 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

23 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 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), Lu KB et al., Macromolecules, 2008, 41 (21), iPP + CNT iPP

25 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), Lu KB et al., Macromolecules, 2008, 41 (21), TEM: Transcrystalline interphase around CNT J. Loos (TU Eindhoven, The Netherlands) Sketch for possible nucleation mechanism

26 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 27 Thank you

28 28 Polymer-fullerene blends for solar cells – P3HT / PCBM DSC results P3HT / PCBM P3HT:semi-crystallineT g ca °C, T m ca. 210°C, T c ca. 180°C PCBM:semi-crystallineT m ca. 280°C, T c ca. 250°C For both P3HT and PCBM, crystallisation retarded in presence of second component Formation nano-morphology by dual crystallization 1 st cooling 2 nd heating P3HT T g Crystallisation PCBM P3HT T g Melting Melting PCBM Crystallization

29 29 Polymer-fullerene blends for solar cells – pure PCBM MTDSC on sample aged at 103°C for 4000 min


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