STUDYING THE DEPENDENCY OF INTERFACIAL FORMATION WITH CARBON

Transcription

1 STUDYING THE DEPENDENCY OF INTERFACIAL FORMATION WITH CARBON AFOSR Low Density Materials Program Review Program Manager: Dr. Joycelyn Harrison (FA ) Wright Brothers Institute, Tech^Edge Dayton, OH June 4 th to 5 th, 2012 Marilyn L. Minus Assistant Professor Department of Mechanical and Industrial Engineering Northeastern University, Boston, MA

2 2 Motivation - Objectives Understand the formation of interfacial polymer in the nano-composite fiber Understand processing conditions for the promotion of interfacial polymer in the composite fibers Determine property-structure relationships Polymers of Interest in this work: Polyacrylonitrile (PAN) Carbon fiber applications Polyvinyl alcohol (PVA) many successful studies of CNT composite with high-mechanical performance. Polyethylene (PE) baseline study for crystalline structure of the interface

3 3 Various Nano-Carbon Fillers Nano-Carbon Shape Smallest Dimension (nm) Aspect Ratio Modulus (GPa) Nano-Fiber rod 50 to 100 (diameter) Multi-wall carbon nanotubes (MWNT) Single-wall carbon nanotubes (SWNT) Graphene/ Nanographite Carbon nano-chip fibers (CNCF) Graphene nano-ribbons (CVD grown) rod 5 to 50 (diameter) 100 to 10,000 1,000 rod 0.6 to 2 (diameter) 100 to 10,000 1,000 plate 0.4 to 10 (thickness) 100 to ,000 tape 10 to 500 (width/thickness) tape 5 to 20 nm (width/thickness) 100 to ,000 >100 1, nm Carbon Nano-Chips Graphene Nano-Ribbons Winey, et al. MRS Bulletin 2007 Campos-Delgado et al. Nano Letters 8 (9), 2008

4 4 STUDY ON CARBON NANOTUBE DISPERSIONS

5 5 Importance of Good SWNT Dispersion Schematic of the Polymer Chains in the Near Vicinity of SWNT Poor nanotube dispersion can induce severe stress concentration in matrix 5 µm Preservation of the CNT structure in polymer composites is essential to fully exploit their ability to template polymer crystallization and orientation, and to maximize reinforcement. M. L. Minus et al., 2009, Macromolecular Chemistry and Physics. Y. Zhang, M.L. Minus (In preparation)

6 6 Dispersing SWNT large aspect ratio van der Waals interactions self-arranged into ropes or bundles Current dispersing techniques Chemically Functionalization Surfactant Dispersant Can interupt the interfacial interactions between SWNT walls and polymer matrix Mechanically Sonication Homogenization Forming true solutions (< 20mg/L) in NMP, DMF, DMA Scission by cavitation or shear flow Dispersing method used Sonicating SWNT in pure solvents or dilute polymer solutions at 20 mg/l S. Wang et al., 2008, Nanotechnology. M. Calvaresi et al., 2009, Small. G. W. Lee et al., 2005, J. Phys. Chem.

7 Reduction of SWNT Length during Sonication in Pure Solvent µm SWNT array 200 nm Regardless of the initial SWNT length, after ~30hr cavitation forces during sonication break SWNT lengths by more than 90%. SWNT powder Y. Zhang, M.L. Minus (In preparation)

8 8 Self-Reorganization of CNT by Crystalline Symmetry Reaggregation is a function of sonication time. longer sonicated nanotubes displayed both a faster rate and a higher degree of reaggregation. SWNT 2D Hexagonal Crystal Packing Potential reasons for reaggregation: Tube shortening reduces curvature. Bundle exfoliation reduces diameter. CNT crystalline symmetry improves. CNT pack into 2D crystals. Y. Zhang, M.L. Minus (In preparation) before during after

9 Small-Angle X-ray Scattering Analysis SWNT Bundle Exfoliation as a Function of Sonication Time 9 Two dominant populations. Large bundles exfoliate during early sonication, but reaggregate during extended sonication. Small bundles maintain nearly unchanged size. Y. Zhang, M.L. Minus (In preparation)

10 Volume Fraction of Bundles (%) Volume Fraction of Bundles (%) 10 Small Angle X-ray Scattering Analysis Bar Plots for Distribution of Bundle Populations SWNT Powder SWNT Array Sonication Time (hr) Sonication Time (hr) Small Bundles Large Bundles Small Bundles Large Bundles For SWNT powder, best exfoliations can be obtained between 48 hr and 72 hr. For SWNT array, sonication beyond 48 hr induced severe reaggregations. Y. Zhang, M.L. Minus (In preparation)

11 Conclusions 11 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry.

12 POLYMER-ASSISTED SWNT DISPERSION: INTERFACIAL MORPHOLOGY AND STRUCTURE 12

13 13 Polymer-Assisted SWNT Dispersion Both being left unperturbed for 2 hr, polymerassisted sonication largely prevented reaggregation of SWNT. Y. Zhang, M.L. Minus (In preparation) Polymer wrapping around exfoliated SWNT bundles prevents reaggregation. Increased solution viscosity due to the presence of polymer can reduce breakdown of tubes during sonication.

14 Polymer Crystalline Coating on CNT 14 Folded Fringe-Micelle Model Hybrid Fringe-Micelle Model With the presence of SWNT, polymer tends to form crystallites in the vicinity of the nanotubes. Y. Zhang, M.L. Minus (In preparation)

15 Various Polymer-SWNT Interfacial Coating Structures 15 Crystalline PAN shows uniform coating on SWNT Amorphous PAN shows dewetting from SWNT Hybrid coating structure of PVA on SWNT Crystalline PAN forms kabobs on SWNT shish Wide-angle X-ray data for PVA/SWNT sample (above) shows sharp crystalline peaks for the PVA coating on SWNT. The average PVA crystal size is 50 nm (33-81 nm) similar to the coating thickness on the SWNT. Interfacial PVA layer is almost entirely crystalline. M. L. Minus et al., 2006, Polymer. Y. Zhang, M.L. Minus (In preparation)

16 PAN Interfacial Coating on SWNT Sonication conditions greatly affect the formation of interfacial coating of PAN on SWNT 16 Amorphous coating: Rapid quenching of dilute solution of polymer in the presence of sonicating SWNT Crystalline coating: Slow cooling of dilute solution of polymer in the presence of sonicating SWNT Shish Kebab coating: Controlled ΔT (degree of undercooling) of dilute solution of polymer in the presence of sonicating SWNT

17 PVA Interfacial Coating on SWNT Sonication conditions less of an issue for the formation of interfacial coating of PVA on SWNT **PVA able to crystallize more readily than PAN (i.e. bulky side group) 17 Hybrid (Crystalline + Amorphous) coating: Slow cooling of dilute solution of polymer in the presence of sonicating SWNT Crystalline (Tubular) coating: Controlled ΔT (degree of undercooling) of dilute solution of polymer in the presence of sonicating SWNT PVA chain conformation: zig-zag Crystal Structure: Monoclinic PAN chain conformation: helical; could have planar zig-zag segments Crystal Structure: Orthorhombic/Hexagonal

18 Polymer/SWNT Interfacial Structure Observed in Macroscopic Composite Materials PAN/SWNT composite PAN/CNT film composite film 18 PVA/SWNT composite film Schematic fractured surfaces of a composite film Clear Presence of Polymer/CNT Interfacial Region in the Bulk Composite at Fractured Surfaces Y. Zhang, M.L. Minus (In preparation)

19 Future Plans Study of the Properties by AFM or Nano-Indentation 19 Polymer coated SWNT Challenges: Testing the mechanical properties of the interfacial polymer-nanotube regions directly via AFM or nano-indentation Determine the optimal polymer and SWNT concentrations to form the desired coating structure. Isolate and deposit the coated SWNT (or SWNT bundles) on a certain substrate. Nano probe Y. Zhang, M.L. Minus (In preparation)

20 Future Plans Looking into the Stress Transfer Properties between Interfacial Polymer and Bulk Polymer 500 nm 100 nm PAN coating on CNT PVA film PVA sonicated under conditions used for CNT dispersion then added to PVA bulk polymer before casting film Deposited on bulk PAN film Gap present between the bulk and interfacial PAN Single Crystals present in the final film separated from the bulk

21 Conclusions 21 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry. Polymer-assisted sonication enables polymer chains to exfoliate and wrap around SWNT bundles during a dynamic process. The polymer interfacial coating structures on SWNT, especially crystallized tubular coating, can dictate the best properties of polymer nano-composites.

22 GEL-SPINNING OF POLY(VINYL ALCOHOL)/CARBON NANO-CHIP FIBER COMPOSITE TAPES 22

23 WAXD images SEM images Morphology Analysis 23 Evident fibrillar structure PVA fracture surface PVA/CNCF fracture surface 002 graphitic peak Higher orientation PVA PVA/CNCF Kenan Song, Marilyn L. Minus et al. J. Appl. Polym. Sci. (2012)

24 Mechanical Properties 24 Sample PVA PVA/CNCF Remark Draw ratio 6 10 CNCF lubrication effect E, (GPa) 7.3 ± ± % increase σ, (GPa) 0.17 ± ± % increase ε max, (%) 18.3 ± ± 0.7 Toughness, (J/g) 16.1 ± ± % increase Toughness, (J/g) ~2 ~28 Small strain < 5% Toughness approaches Kevlar (28-36 J/g) Small-strain toughness has applications in bullet-proof vest, shielding, helmet protections et al. Kenan Song, Marilyn L. Minus et al. J. Appl. Polym. Sci. (2012)

25 SAXS images WAXD images Crystal Structural Analysis 25 PVA chains orientation along the tape axis is much higher in the composites. PVA PVA/CNCF Herman s Orientation (f) Misorientation (º) Long-order (nm) PVA PVA/CNCF Intensity versus q, SAXS curves Peak along meridian axis indicates periodic stacks of crystalline lamellae orientated along the fiber axis. Parallel crystalline stacks of the same width with different thickness. Conclusion: Composite display larger periodic stacking of the crystalline lamellae.

26 Morphology Analysis 26 sonication As-received CNCF Sonicated PVA/CNCF solution TEM image of sonicated CNCF

27 Nano- Carbons Mechanical Properties 27 Sample PVA PVA/CNCF Remark E, (GPa) 7.3 ± ± % increase Rule-of-Mixture: E c VE f f V E m1 m1 E f (GPa) V f E f, (GPa) V m1 E m1 (GPa) E c (GPa) f*v m2 *E m2 (GPa) SWNT Fully oriente d MWNT SLG FLG WAXD images Lee, C. et al. Sci. 2008, 321, 385. Yu, M.-F. et al. Phys. Rev. Lett. 2000, 84, Treacy, M. M. J. et al. Nat. 1996, 381, 678. Rasuli, R. et al. Nanotechnol. 2010, 21, Frank, I. W. et al. J.Vac. Sci. Technol. B 2007, 25, Poot, M. et al. App. Phys. Lett. 2008, 92, Liu, T. et al. Nano letters 2003, 3, 647. Low! Note: E m1, control tapes modulus; E m2, theoretical modulus of PVA, 255 GPa; f, Herman s orientation;

28 Mechanical Strengthening Analysis 28 Ec =VfEf +Vm1Em1 E c =V f E f +V m1 E m1 +V m2 E m2 Nano- Carbons E f (GPa) V f E f, (GPa) V m1 E m1 (GPa) V m2 E m2 (GPa) V m2 (%) SWNT MWNT Fully oriented SLG Misaligned FLG SWNT ropes Lee, C. et al. Sci. 2008, 321, 385. Yu, M.-F. et al. Phys. Rev. Lett. 2000, 84, Treacy, M. M. J. et al. Nat. 1996, 381, 678. Rasuli, R. et al. Nanotechnol. 2010, 21, Frank, I. W. et al. J.Vac. Sci. Technol. B 2007, 25, Poot, M. et al. App. Phys. Lett. 2008, 92, Liu, T. et al. Nano letters 2003, 3, 647. Kenan Song, Marilyn L. Minus et al. J. Appl. Polym. Sci. (2012)

29 Conclusions 29 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry. Polymer-assisted sonication enables polymer chains to exfoliate and wrap around SWNT bundles during a dynamic process. The polymer interfacial coating structures on SWNT, especially crystallized tubular coating, can dictate the best properties of polymer nano-composites. Morphology of the nano-carbons have an significant effect on the interfacial interaction with the matrix, and the resultant matrix microstructure development.

30 POLYMER/CARBON NANOTUBES COMPOSITE FIBERS BY USING STEADY SHEAR-FLOW

31 Increasing the Interfacial Polymer Low CNT loading (~1 wt%) Limited Exfoliation (~ bundle size 5 to 20 nm) Interfacial thickness: 15 to 100 nm (experimental observations) CURRENT Significantly increase interfacial thickness by promoting crystallization CNT Composite Fiber POTENTIALS Significantly increase CNT concentration

32 32 Micro-Structural Schematic Schematic of: (i) solvent molecules inter-dispersed between the polymer chains which allows for movement of the chains and assist alignment of the polymer chains during spinning, (ii) polymer chains and solvent molecules inter-dispersed between CNT bundles/ropes to assist alignment of the CNT during spinning.

33 Nanotechnology 22 (2011) Advantages of Using Polymers Nanotechnology 22 (2011) Figure 2. Schematic of the polymer/cnt composite manufacturing process: wafer (1), web (2), sliver (3), squeeze rollers (4), furnace (5), guide rods (6), yarn (7), bobbin (8) and polymer applicator (9). Pure CNT Yarns Modulus 27 GPa Strength 0.3 Gpa Zhang, M. et al., Science 2004, 306 (5700), K. R. Atkinson et al. Physica B, 2007, 394, C-D Tran. et al., Nanotechnology 2011, 22, Why polymer is important? Figure 7. Micrograph (SEM images) of the surface layer for CNT yarn using the modified pr CNT yarn. Figure 3. Preparation of CNTPU/ web/sliver: CNT Fiber micrograph of a CNT sliver using the modified dry spinning Modulus process 150 shows GPa the CNT bundle alignment. Strength 2 Gpa Figure 4. capillary e of the first of polyme section of polymer s (6, 7). of the co used for

34 Shear-Flow Spinning Set-Up 34 Cylindrical stir bar to create shear flow (50 to 300 RPM) Methanol Ice bath Tensile Force Hot plate As-Spun Fiber Syringe use for polymer solution injection Hot-drawn Fiber Various kinds of CNT and polymer fibers can be spun using this set-up The steady shear flow helps the alignment for both CNT and polymer chains by introducing shear force along fiber direction Initial draw ratio can be well controlled by adjusting both take-up speed and injection speed Fibers with up to 50 wt% CNT loading have spun successfully

35 PVA/SWNT 10 wt% Fiber Morphology μm Fiber Diameter ~ 40 to 60 μm 10 μm Fiber Diameter ~ 9 to 12 μm 50 μm PVA/ SWNT As-spun fiber (10 wt%) Hot Drawing 50 μm PVA/ SWNT fiber after hot drawing (10 wt%) Fracture surface of PVA/SWNT drawn fiber (10 wt%) 1 μm 10 μm

36 PVA/SWNT Mechanical Properties 36 Modulus Increase by 450% Strength Increase by 200% a b (a) Hot drawn PVA control fiber (b) Hot drawn PVA/SWNT 10 wt% fiber SWNT Loadings Draw Ratio Modulus (GPa) Strength (GPa) Elongationto-Break (%) Toughness (J/g) PVA Control ± ± ± wt% ± ± ±

37 Conclusions 37 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry. Polymer-assisted sonication enables polymer chains to exfoliate and wrap around SWNT bundles during a dynamic process. The polymer interfacial coating structures on SWNT, especially crystallized tubular coating, can dictate the best properties of polymer nano-composites. Morphology of the nano-carbons have an significant effect on the interfacial interaction with the matrix, and the resultant matrix microstructure development. Small amount of polymer acts as a plasticizer to help align CNT and improve stress transfer in the composite.

38 PROMOTING EXTENDED-CHAIN CRYSTALLIZATION POLYETHYLENE CARBON NANOTUBES STUDIES UNDER SHEAR FLOW

39 39 Introduction Shear flow helps to align crystals Orientation greatly affects mechanical properties A. J. Pennings, Makromol. Chem., Suppl. 2, p (1979) M. L. Minus, H. G. Chea, S. Kumar, Polymer 47, p (2006)

40 PE & PE/SWNT Drawing done at 130 C Draw Ratio 2-12x Control Fiber - Unwashed As-spun SWNT fiber 1 μm nm Drawn SWNT fiber 100 μm 1 μm Control Fiber - Drawn 1 μm 100 μm 400 nm 500 nm

41 41 Differential Scanning Calorimetry **Shift to higher melting temperature due to orthorhombic to hexagonal transition arises due to the presence to more extended chains which consists of planar zig-zag and helical segments (mixture of gauche and trans) As-spun Drawn at 130 C

42 Comparison of Mechanical Properties 42 Drawing E (GPa) ε (%) σ max (MPa) Increase in Stiffness Increase in Strength Control PE Control PE Drawn at 130 C PE/SWNT Undrawn PE/SWNT Drawn at 130 C % 181% % 812%

43 New Shear Flow Set-Up Front View Side View Reservoir Polymer/So lvent Injection points Pump Take-up Roller Heating Zones Basin

44 Conclusions 44 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry. Polymer-assisted sonication enables polymer chains to exfoliate and wrap around SWNT bundles during a dynamic process. The polymer interfacial coating structures on SWNT, especially crystallized tubular coating, can dictate the best properties of polymer nano-composites. Morphology of the nano-carbons have an significant effect on the interfacial interaction with the matrix, and the resultant matrix microstructure development. Small amount of polymer acts as a plasticizer to help align CNT and improve stress transfer in the composite. Basic crystallization studies between PE and SWNT show their ability to promote extended-chain polymer structure in the composite. Shows the special implications of nanotubes to promote unique polymer micro-structures.

45 Conclusions 45 Major Conclusions Initial sonication drastically breaks SWNT, but extended sonication does not further shorten the tubes below a critical length. The nanotube reaggregates more readily with sonication time, suggesting hierarchical rearrangement due to the increased tube crystalline symmetry. Polymer-assisted sonication enables polymer chains to exfoliate and wrap around SWNT bundles during a dynamic process. The polymer interfacial coating structures on SWNT, especially crystallized tubular coating, can dictate the best properties of polymer nano-composites. Morphology of the nano-carbons have an significant effect on the interfacial interaction with the matrix, and the resultant matrix microstructure development. Small amount of polymer acts as a plasticizer to help align CNT and improve stress transfer in the composite. Basic crystallization studies between PE and SWNT show their ability to promote extended-chain polymer structure in the composite. Shows the special implications of nanotubes to promote unique polymer micro-structures.

46 46 Acknowledgements MINUS Lab Research Group Dr. Yunume Obi (Post Doc.) Yiying Zhang (Ph.D) Kenan Song (Ph.D) Emily Green (Ph.D) Jiangsha Meng (Ph.D) Navid Tajaddod (M.Sci) Stephen Strassburg (B.Sci.) Stephen R Uram (B.Sci.) Andrew Waite (B.Sci..) Prof. Yung Joon Jung, Northeastern University (providing CNT arrays) Center for High-rate Nano-manufacturing, Northeastern University Air Force Office of Scientific Research (AFOSR) Department of Defense Defense University Research Instrumentation Program (DURIP) (research funding for wide-angle and small-angle X-ray systems)