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1 30 Ossipee Road P.O. Box 9101 Newton, MA Phone: Fax: TEST REPORT De-agglomeration of Carbon Nanotubes Using Microfluidizer Technology Prepared by: Thomai Mimi Panagiotou, Ph.D. John Michael Bernard Steven Vincent Mesite 09/07/2005

2 SUMMARY Product: Dispersions of single-wall and multi- wall carbon nanotubes (MWNT or SWNT) in polymer resins, mineral oil, organic solvents and water. Objective: De-agglomeration of carbon nanotubes (CNT) to be used for low weight composites with enhanced mechanical and electrical properties. Conclusions: Microfluidizer technology was successful in de -agglomerating carbon nanotubes in a variety of media including polymer resins, mineral oil, organic solvents and water, with CNT concentration in the range of %. The length of the CNTs was reduced in a controlled manner based on the processing conditions. The technology was effective with both single-wall and multi- wall nanotubes as inferred from FESEM analysis, optical microscopy and particle size analysis. Recommendations: Microfluidizer M-110Y (pneumatic) or M-110EH (electro-hydraulic) for lab scale, or Microfluidizer M-700 series for production scale Chamber types: (a) H30Z (200 microns)-g10z (87 microns), or (b) H230Z (400 microns)-h210z (200 microns) depending on the dispersant fluid, the concentration of the carbon nanotubes and the desired final aggregate size Processing of the resin-based formulations at elevated temperatures Cooling of the material after processing 1(a) Unprocessed 1(b) 1 pass H30Z & 23,000 psi Figure 1. Images captured with an FESEM at 20,000X magnification depicting (a) unprocessed and (b) processed single wall carbon nanotubes in high viscosity mineral oil. 2

3 1. Background Carbon Nanotubes Carbon nanotubes (CNT) are seamless cylinders which consist of graphite (graphene) closed at either end with caps[1]. Depending on the number of cylinders one inside the other, the carbon nanotubes can either be single-wall (SWNT) or multi-wall (MWNT) nanotubes. They have a very high aspect ratio, with diameters varying from nanometers for SWNT to up to 20 nanometers for MWNT, while they can be a few millimeters long. The carbon nanotubes have remarkable mechanical, electrical and thermal properties[2-7]. They are 100 times stronger than steel with a sixth of the weight and they are as stiff as diamond. Depending on the way the graphite structure spirals around the tube, and other factors such as doping, the CNTs can be electrical conductors, semiconductors or insulators. In addition, they have thermal conductivity as high as that of diamond. Such properties make CNTs candidates for a variety of applications which require high performance materials[8-11]. Applications of CNTs include: conductive and high tensile strength composites; field emission displays; energy conversion and energy storage devices; nanometersize electronic devices; sensors; medical diagnostics; hydrogen storage. In order to achieve paramount performance, the carbon nanotubes must get de-agglomerated, frequently shortened and uniformly dispersed in media such as organic solvents, polymer resins, water, etc.[10-12]. De-agglomerated CNTs form networks and such networks are responsible for enhanced strength and electrical conductivity of polymer composites containing CNTs. Without proper dispersion, CNT composites perform no better than carbon black composites. These require large amounts of carbon black to achieve significant electrical conductivity and such amounts are usually detrimental to the mechanical properties of the composites. Any method used to de-agglomerate CNTs should be efficient, economical and scalable. Sonication is a method that is often used in lab scale to de-agglomerate and shorten the CNTs. This method does not scale up and may contaminate the CNTs with metal particles from the sonication probe. In addition, it may change the chiral properties of the nanotubes[12]. Functionalization of CNT surfaces to improve dispersion could improve dispersion but does not solve the problem fully and is still in research stage[11]. Microfluidizer technology provides a viable solution to dispersing the CNTs in a variety of media and also to shorten the length of the CNTs, if needed. The technology is fully scalable and has been used for two decades to disperse and reduce the particle size of powders in liquid media. Microfluidizer Processors Microfluidizer processors are high shear fluid processors that are very effective in particle deagglomeration and size reduction. These processors produce shear in the order of magnitude of 10 6 s -1, which is several orders of magnitude higher than that of conventional mixing equipment. The shear is applied uniformly to the material, so the final product is characterized by narrow particle size distribution. 3

4 The Microfluidizer processors are capable of pressurizing streams of liquid up to 40,000 psi and forcing them through tiny orifices, in the range of 100 microns. They provide continuous processing with flowrates in the range of liters/minute in a completely scalable fashion. 2. Material Processing Equipment: Microfluidizer unit Lab scale: Industrial scale: Interaction chambers: Electron Microscope: Optical Microscope: Particle size analyzer: -M110Y or M110EH - M700 series - H230Z (400 microns) - H210Z (200 microns) - H30Z (200 microns) - G10Z (87 microns) - F20Y (75 microns) - Zeiss - Supra25 FESEM - Olympus BH-2 optical with attachments - Horiba LA-910 laser scattering particle size analyzer Relative Refractive indices: i (water as diluent) i (toluene as diluent) Procedure: All materials in the formulation were mixed well before processing. Table 1 shows a list of carbon nanotube formulations processed using Microfluidizer processors. The processing conditions (pressure, number of passes and chamber size), shown in Table 2, were determined by the requirements of the final product and the rheological properties of the fluid. The processed samples were analyzed by a combination of techniques, including optical microscopy, Field Emission Scanning Electron Microscope (FESEM) and particle size analysis. Table 1. CNT formulations processed with the Microfluidizer Technology Sample Solids Content Nanotube Type Dispersant Surfactant % SWNT High viscosity mineral oil % SWNT High viscosity mineral oil % SWNT Polymer resin % SWNT Water 1 % % SWNT Toluene % MWNT Methanol % MWNT Methanol 1 % % MWNT Methanol % MWNT Methanol 1 % 4

5 FESEM was used to determine the extent of de-agglomeration and length reduction of SWNTs dispersed in high density mineral oil. Samples for FESEM analysis were prepared by placing a drop of the dispersion on a piece of aluminum foil and then heated to over 180ºC for 10 minutes to burn off the oil. Table 2. Processing conditions of CNT formulations Sample Solids Content Dispersant Pressure (psi) (# of passes) Chamber Combination (size in microns) % SWNT High viscosity mineral oil 23,000 (1) H30Z-G10Z (200-87) % SWNT High viscosity 23,000 (1-20) same mineral oil % SWNT Polymer resin 23,000 (1-3) same % SWNT Water 23,000 (1-4) same % SWNT Toluene 23,000 (1) same % MWNT Methanol 12,000-17,000 (1) H230Z-H210Z ( ) % MWNT Methanol 12,000-17,000 (1) same % MWNT Methanol 12,000-17,000 (1) same % MWNT Methanol 12,000-17,000 (1) same 3. Results The effects of processing 0.38% SWNT carbon nanotubes dispersed in high density mineral oil can be seen in images of the material captured with an FESEM, see Figure 2. The unprocessed nanotubes, Figure 2(a), are densely packed and the individual nanotube strands are not discernable. After a single pass, individual long and thin tubes can be clearly seen, see Figure 2(b). The CNTs appear much more de-agglomerated and forming a network. They are also uniformly dispersed throughout the media. It is not clear that these are individual nanotubes or thin strands but their diameter is fairly uniform. Additional passes shorten such strands, without necessarily decreasing the diameter of the strands, see Figures 2(c) and 2(d). 5

2(a): Unprocessed 2(c): 10 passes H30Z-G10Z @ 23,000 psi 2(b): 1 pass H30Z-G10Z @ 23,000 psi 2(d): 20 passes H30Z-G10Z @ 23,000 psi Figure 2.

Each picture corresponds to different number of passes through the Microfluidizer processor, ranging from 020 passes.

6 2(a): Unprocessed 2(c): 10 passes 23,000 psi 2(b): 1 pass 23,000 psi 2(d): 20 passes 23,000 psi Figure 2. Images captured with an FESEM at 20,000 X magnification. Each picture corresponds to different number of passes through the Microfluidizer processor, ranging from 020 passes. Figures 3 and 4 show pictures of carbon nanotube dispersions captured by optical microscopy. Processed SWNT depicted in Figure 3b are so well dispersed that the individual entities can barely be seen. Processed MWNT shown in Figure 4b indicate that after de-agglomeration the particles resemble thin fibers having high aspect ratio. 6

3(a): Unprocessed 3(b): 1 pass H30Z-G10Z @ 23,000 psi Figure 3.

The particles are so well dispersed; they are barely discernable with optical microscopy. 4(a): Unprocessed 50 µm 4(b): 1 pass H210Z-H230Z @ 17,000 psi Figure 4.

Particle size analysis of processed and unprocessed CNT dispersions was used to determine the presence of large agglomerates in the sample, as those shown in Figures 3a and

The measurements were taken with the Horiba LA 910 particle size analyzer.

7 3(a): Unprocessed 3(b): 1 pass 23,000 psi Figure 3. (a) Unprocessed SWNT; (b) SWNT with a median aggregate size of 363 nanometers after being processed at 23,000 psi for 1 pass with the H30Z-G10Z chambers configuration. The particles are so well dispersed; they are barely discernable with optical microscopy. 4(a): Unprocessed 50 µm 4(b): 1 pass 17,000 psi Figure 4. (a) Unprocessed MWNT; (b) MWNT after being processed at 17,000 psi for 1 pass with H210Z- H230Z chambers using the M-110Y unit. Particle size analysis of processed and unprocessed CNT dispersions was used to determine the presence of large agglomerates in the sample, as those shown in Figures 3a and 4a. Figure 5 shows particle size analysis results of a 1% SWNT dispersion in water before and after processing. The measurements were taken with the Horiba LA 910 particle size analyzer. It can be seen that the average particle size of the sample decreased almost 100 fold from over 35 microns (35,000 nm) to microns (363 nm) in four passes. In addition, the processed material does not contain agglomerates over 2 microns, an indication that the SWNTs are uniformly dispersed in water. The de-agglomerated particles, in contrast with the agglomerates, have high aspect ratios. Therefore the measured particle sizes of the dispersed particles do not necessarily correspond to 7

8 actual dimensions of the particles. The sizes of the dispersed, high aspect ratio particles should be interpreted as effective dimensions, as perceived by the instrument. Nevertheless, these measurements demonstrate clearly an overall decrease in particle size and the lack of agglomerates in the processed material. Frequency (volume %) Unprocessed Particle size (microns). 4 passes 23,000 psi Figure 5. Particle Size Distributions of a 1% SWNT dispersion in water, before and after processing with H30Z-G10Z chamber configuration at 23,000 psi. The Microfluidizer processor reduced the median aggregate size from microns to microns. 4. Summary Microfluidizer technology was successful in de-agglomerating SWNT and MWNT, and creating stable suspensions of nanotubes in various liquid media. The liquid media included polymer resins, organic solvents, mineral oil and water and the concentration of carbon nanotubes varied in the range of %. Microscopy, both electron and optical, confirmed that the nanotubes were de-agglomerated to a large extent and dispersed uniformly in the dispersion media in a single pass. Additional passes result in length reduction of the nanotubes. One of the distinct advantages of Microfluidizer technology is that the amount of shear that is applied on the material can be easily varied, allowing the nanotubes to detangle and be shortened to the extent required by any application. 8

9 5. References 1. "Helical microtubules of graphitic carbon", S. Iijima, Nature 354, 56 (1991). 2. Electronic structure of graphene tubules based on C 60 ", R. Saito, M. Fujita, G. Dresselhaus and M. S. Dresselhaus, Phys. Rev. B 46, 1804 (1992). 3. Structural Rigidity and Low Frequency Vibrational Modes of Long Carbon Tubules", G. Overney, W. Zhong, and D. Tománek, Z. Phys. D 27, 93 (1993). 4. Individual single-wall carbon nanotubes as quantum wires", SJ Tans, M H Devoret, H Dai, A Thess, R E Smalley, L J Geerligs and C Dekker, Nature, 386, 474 (1997). 5. "Unraveling Nanotubes: Field Emission from an Atomic Wire", A.G. Rinzler, J.H. Hafner, P. Nikolaev, L. Lou, S.G. Kim, D. Tománek, P. Nordlander, D.T. Colbert, and R.E. Smalley, Science 269, 1550 (1995). 6. Unusually High Thermal Conductivity of Carbon Nanotubes", Savas Berber, Young- Kyun Kwon, and David Tománek, Phys. Rev. Lett. 84, 4613 (2000). 7. M. Kociak, A. Yu. Kasumov, S. Guéron, B. Reulet, I. I. Khodos, Yu. B. Gorbatov, V. T. Volkov, L. Vaccarini, and H. Bouchiat, Phys. Rev. Lett. 86, 2416 (2001). 8. Storage of hydrogen in single-walled carbon nanotubes", A C Dillon, K M Jones, T A Bekkendahl, C H Kiang, D S Bethune and M J Heben, Nature, 386, 377 (1997). 9. Engineering Carbon Nanotubes and Nanotube Circuits Using Electrical Breakdown", P.C. Collins, M.S. Arnold, and P. Avouris, Science 292, 706 (2001). 10. Colbert, Daniel T, Single-wall Nanotubes: A New Option for Conductive Plastics and Engineering Polymers. Plastics Additives & Compounding. January/February Carbon Nanotubes: A Small Scale Wonder. Chemical Engineering, February Sonication-induced changes in chiral distribution: A complication in the use of singlewalled carbon nanotube fluorescence for determining species distribution. Heller, D.A., Barone, P.W. and Strano, M.S., Carbon, 43, (2005). 9

Car bo n Na no-t ube s: An Ov er view BY ARUNDUBEY ROLL NO. 0905EC ELEX. & COMM. DPTT. I. T. M., GWALIOR

Car bo n Na no-t ube s: An Ov er view BY ARUNDUBEY ROLL NO. 0905EC071033 ELEX. & COMM. DPTT. I. T. M., GWALIOR Pre se nta tion O ve rvie w Definition History Properties Current Application Manufacturing