Carbon Black Dispersions: Minimizing Particle Sizes by Control of

Chapter 12

Carbon Black Dispersions: Minimizing Particle Sizes by Control of Processing Conditions 1

2

1,*

Downloaded by UNIV MASSACHUSETTS AMHERST on August 4, 2012 | http://pubs.acs.org Publication Date: January 21, 2005 | doi: 10.1021/bk-2005-0891.ch012

D. Forryan , D. Rasmussen, and R. Partch 1

Department of Chemistry and Center for Advanced Material Processing, Clarkson University, 8 Clarkson Avenue, Potsdam, NY 13699-5814 Department of Chemical Engineering, Clarkson University, 8 Clarkson Avenue, Potsdam, NY 13699-5705 2

The objective of the this work was to determine a technique for reducing the particle size of commercial carbon black aggregates for their possible use as laser absorbing fillers in optical lenses. Aggregate size in the range of 40-80nm has been achieved using one commercial carbon black sample in both water and a chlorinated organic solvent, using an ultrasonic horn and argon purge to create the dispersion. Addition of anionic, cationic or nonionic surfactant to the solvent before processing did not result in further size reduction. Cabot Monarch 1100 large carbon black aggregates composed of primary particles having 15-20nm diameter gave the best results. After processing the dispersions were stable for over twenty-four hours and after precipitation occurred, redispersion to the 40-80nm aggregates was achieved using only an ultrasonic bath.

170

© 2005 American Chemical Society

In Defense Applications of Nanomaterials; Miziolek, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

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Introduction Complete and uniform dispersibility of fillers in a matrix is a prerequisite for a composite to have optimum properties. Regardless of composition, shape or size of the particles, less than optimum distribution in, for example, ceramic, metal or polymer material can result in lower mechanical strength, random discoloration or decreased electrical or thermal conductivity. For these and other reasons much effort has been and continues to be devoted to understanding fundamental reasons why some powders readily disperse in a medium and others do not. It is clear from many historic studies (1-4) that the surface chemistry of a particle, which dictates relative hydrophilicity-hydrophobicity and zeta potential, is the dominant factor. Benefits of perfected filler dispersibility are found in dental resins (5), personal body armor (6), cosmetics and sunscreens (7), rubber products (5), latex paint (P), metal matrix composites (70), inks and gels (77), many foods, and in abrasive slurries used for chemical mechanical planarization (CMP of wafers during computer chip manufacture (12). For decades colloid scientists have prepared and characterized multi- and sub-micron sized particles to the extent that processing equipment and analytical instrumentation allowed. But the routinely handled sub-micron species, now called nanoparticles, were produced only in small quantities and usually in dilute dispersions (73). The development of scaled-up methods for synthesizing and collecting nanoparticles of single or mixed composition has caused a revolution in composite engineering, which has already resulted in material properties previously unavailable (14,15). But the price to pay as filler particle sizes are reduced to nano scale is their greater tendency to form soft or hard (fused) aggregates of the primary units, especially when in the dry state. Their surface areas are so large that Van der Waals forces of attraction inhibit their separation when mixed into a matrix. Large sized aggregates of nanoparticles dispersed in a matrix are not capable of enhancing the properties of a composite to the same degree as are smaller aggregates or unaggregated primary species. The recent availability of many types of dry nanoparticle fillers requires that techniques be devised to break apart the aggregates and to process the asgenerated smaller units before they re-assemble. The objective of the current study was to determine conditions by which carbon black powder aggregate sizes can be minimized below previously reported values and stabilized in various liquid media. The incentive was to provide filler theoretically (16) capable of absorbing laser radiation for use in optical lenses.


172

Discussion


Starting Materials Powdered carbon formed by natural or artificial combustion or pyrolysis of organic material has existed for centuries and been employed for a wide variety of uses (17-20). The dry powders are generally in the form of aggregates greater than lOOnm in size and do not de-aggregate into primary nanoparticles when placed in a liquid even with application of high energy mixing or addition of a surfactant. The latter, like many other organic chemicals such as colorants, flavors and odorants, are well known to adsorb strongly to the surfaces of the carbon aggregates. Four representative types of commercial carbon black samples were selected for use in the present study. As shown in Table I they were all of the Cabot Monarch variety and exhibited a range of primary nano-particle diameters from 13-16nm, surface areas and oxygen content. All as-received dry samples yielded only aggregates larger than 300nm when manually shaken in water. It was established (21) that the larger aggregates were weakly associated soft assemblies of smaller 40-50nm hard aggregates composed of fused primary particles. Prior to this study the larger aggregates were acceptable as fillers in most composites (22,23). Our goal was to achieve size reduction of particles to less than 50nm in a liquid, which, along with the dispersed carbon nanoparticles, may absorb and dissipate a range of laser photon energies.

Table I. Properties of Cabot Carbon Black Samples Carbon SampleParticle

DBPOil

Nitrogen

1

Density Iodine Number

Size (nm) Adsorption Surface Area (lbs/ft*) (mg/gram) (cc/100 grams)(M2/gram) Monarch 880

16

112

220

8

258220

Monarch 1000

16

no

343

13

500±30

Monarch 1100

14

65

240

15

258120

Monarch 1300

13

100

560

20

665±50

1

All data takenfromCabot product literature.


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Dispersion Procedures and Results Initially, 0.01-0.1wt% amounts of the four Monarch types of carbon black were mixed separately with water and treated as described in Table II. Particle sizes were obtained using both a Brookhaven BI-200SM instrument operating at 514nm and interfaced with a BI-9K digital auto correlator, and an A L V goniometer operating at 647nm. All particle size numbers are weight average with 8-10% deviations. As can be seen, Monarch 1100 carbon black yielded the smallest aggregates. The ultrasonic bath used was of the standard cleaning bath variety common to most laboratories. It's level of energy did not break apart the large soft aggregates any more efficiently than when the mixtures were shaken by hand. Contrary to the above observation, the use of an ACE 600W ultrasonic horn operating at 20 kHzfrequencyand 2.5s pulses with 1.0s intervals, as well as a Microfluidics M-110 microfluidizer, caused Monarch 1100 aggregates to be reduced in size down to 60-80nm clusters of partially fused primary particles. A slow purge of argon gas into the dispersion during sonication facilitated the process (24-28). To the naked eye the samples obtained after microfluidization appeared less dark in color. This could have been due to retention of some amount of the carbon inside the apparatus even though none was evident in wash fluids. An alternative explanation for the slight decolorization is that the fluidization process produces a higher percentage of less than 30nm particles, which is supported by light scattering data. Under the best conditions of treatment none of the other Monarch type carbon black samples yielded desirable results and were therefore not used in further studies. A review of the data in Table I reveals that Monarch 880 carbon black is possibly most similar in chemical and physical property to Monarch 1100 except for density. The iodine number, which indicates reactivity of vinyl and other functional groups, does not correlate with the results in Table II. Monarch 1100 is twice as dense as Monarch 880, which means greater mass per volume. This feature should correlate with tighter packing, possibly due to more interparticle fusion, of the primary carbon black nanoparticles in the aggregates. If this postulate is valid, the observation that the more dense aggregates yield to breakup more efficiently cannot be explained by the current results. Solvent effects on Monarch 1100 dispersions were also investigated. Table III shows the results when 0.1 wt% solids were mixed with water, toluene and hexachlorobutadiene under identical conditions of ultrasound treatment. It is evident that toluene is not a good medium into which any of the Monarch type samples should be dispersed. Furthermore, by comparing with Table II data, water has been superceded by the chlorinated organic as the best of the solvents evaluated to achieve carbon black size reduction. It is not possible to explain the observed trend of solvent effects on particle size reduction by shear or sonic


174 Table II. Conditions for Dispersion of Cabot Carbon Black Samples in Water


1

Dispersion methodParticle size

Carbon black

Media

Monarch 1100

Water

Shakenby hand

>450nm

Monarch 1100

Water

Ultrasonic bath

450nm

Monarch U 00

Water

Sonic horn 0.5 hr

120nm

Monarch 1100

Water/ Argon

Sonic horn 0.5 hr

80nm

Monarch 1100

Water/Argon

Sonic horn 1.0 hr

80nm

Monarch 1100

Water

Microfluidiser

60nm

5 passes Monarch 880

Water/Argon

Sonic horn 0.5 hr

lOOnm

Monarch 1000

Water/Argon

Sonic hom 0.5hr

11 Sum

Monarch 1300

Water

Sonic horn 0.5 hr

214nm

Monarch 1300

Water/Argon

Sonic horn 0.5 hr

128nm

Particle sizes are given as wt. ave. and have 8-10% deviation.

1

Table III. Solvent Effects on Monarch 1100 Particle Size Reduction Carbon Black

Water

Toluene

Hexachloro-1,3butadiene

Monarch 880

100 '

360

200

Monarch 1000

115

440

190

Monarch 1100

80

4300

40

Monarch 1300

130

2070

190

wt. ave. and have 8-10% deviation.


175 Table IV, Effect of Surfactants on Size of Monarch Carbon Black Particles in Water 1

Carbon black

Surfactant level

Particle size (nm)


(on wt carbon) Monarch 880

0.1%PVSA

100

Monarch 880

0.1% Triton

120

Monarch 1000

0.1%PVSA

100

Monarch 1000

0.1%PDDA

130

Monarch 1000

0.1% Triton

160

Monarch 1100

0.1%PVSA

90

Monarch 1100

2.0%PVSA

80

Monarch 1100

0.1%PDDA

80

Monarch 1100

1.0%PDDA

90

Monarch 1300

0.1%PVSA

110

Monarch 1300

0.1% Triton

220

Dispersions treated with sonic horn/argon for 0.5 hr. Particle sizes are given as wt. ave. and have 8-10% deviation. PDDA = poly (diallyldimethylammonium hydrochloride salt) PVSA = poly (vinylsulfonic acid sodium salt) Triton = poly (ethylene oxide) (X-100) energy. Solvent polarity cannot contribute to the difference because toluene and hexachlorobutadiane have similar low values compared to water. The symmetry of the perchlorinated diene prevents it from having much different polarity than toluene. No data is available to compare the energy due to cavitation in the dispersions in the different solvents employed in this study. Other chlorocarbon or chlorohydrocarbon solvents were not investigated in this study because the butadiene had the chemical and physical properties to act synergistically with the finely dispersed carbon to absorb and dissipate laser photon energy (16). The long-term objective is to transfer such effectiveness into optical lens composites for eye protection.



176 Time dependency of the stability of the 40nm and 80nm aggregate dispersions in hexachlorobutadiene and water, respectively, was measured qualitatively. In each case black solid settled to the bottom of the container after 48 hr. The redispersing-settling-redispersing sequence was cycled several times by use of an ultrasonic bath (not horn) and each time the redispersed aggregates returned to the 40-80nm size range. The effect of various surfactants on the above-described procedures in water is shown in Table IV(2P). Comparing particle sizes in water for the four Cabot carbon types in Table III with die data in Table IV reveals that for Monarch 880 neither anionic nor nonionic surfactant helps reduce particle size during sonication. In the case of Monarch 1000 and 1300 particles, the nonionic surfactant has a negative effect (1 IS to 160nm; 130 to 220nm), while the anionic surfactant appears to facilitate slight reduction in particle size (130 to lOOnm). The data in Table IV show that for Monarch 1100 none of the surfactants added to the water during sonication effect a size difference. However, the time dependent stability of Monarch 1100 dispersions in water containing surfactant appeared to be somewhat greater after sonication than without surfactant.

Conclusions Large aggregates of dry, commercial Cabot Monarch 1100 carbon black can be reduced in size to 80nm or 40nm particles in water and hexachlorobutadiene, respectively., by employing sonication. Other types of Cabot carbon black do not yield the same results. Toluene is a poor solvent in which to attempt size reduction. Added surfactants do not cause aggregate size to decrease further during processing but purging the dispersion with argon during sonic hom treatment does. Surfactants increase dispersion stability to some extent. Future research will employ a laser to input energy into carbon black dispersions to determine if further aggregate breakup can be achieved.

Acknowledgments The authors gratefully acknowledge discussions with Andrew Clements and Roger Becker, both associated with US Army TACOM, Michael Sennett with US Army Natick Lab, and with Barbara Severin of AMPTIAC. Financial support came from IITRI and the US Army Contract Office. Facilities were provided by the Center for Advanced Materials Processing at Clarkson University, sponsored by the New York State Science and Technology Foundation.


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References 1. Hydrophobic Surfaces; Fowkes, F.; Ed.; Kendall Award Symposium; Academic Press: New York, NY, 1969. 2. Sato, T.; Ruch, R. Stabilization of Colloidal Dispersions by Polymer Adsorption; Surfactant Science Series; Marcel Dekker: New York, N Y , 1980. 3. Colloidal Dispersions; Goodwin, J.; Ed.; Royal Society of Chemistry Special Publication No. 43; Dorset Press: London, 1981. 4. Colloidal Dispersions; Ottewill., R ; Ed.; Faraday Discussions of the Chemical Society No. 90; Arrowsmith Ltd.: London, 1990. 5. Xu, H.; Eichmiller, F.; Antonucci, J.; Schumacher, G.; Ives, L. Dental Materials 2000, 16, 356-63. 6. Medvedovski, E. Bull. Am. Ceram. Soc. 2002, 81, 27-32. 7. Reisch, M . Chem. & Eng. News. June 24, 2002, p 38. 8. Olmstead, H. Proc. Intertech Conference on Functional Tire Fillers; Intertech Co.: Portland, ME, 2001. 9. Duivenvoorde, F.; van Nostrum, C.; Laven, J.; van der Linde, R. J. Coatings Tech. 2000, 72,145052. 10. Proceedings of the MRS Meeting, Singh, R.; Hofmann, H.; Senna, M.; Partch, R.; Muhammed, M . , Eds.; Materials Research Society: Warrendale, PA, 2002, Vol. 704. 11. Smay, J.; Cesarano III, J.; Lewis, J. Langmuir 2002, 18, 5429-37. 12. Steigerwald, J.; Murarka, S.; Gutman, R. Chemical Mechanical Planarization of Microelectronic Materials; Wiley Interscience: New York, NY, 1997. 13. Matijevic, E. Langmuir 1994, 10, 8-16. 14. Rittner, M . Bull Am. Ceram. Soc. 2002, 81, 33-36. 15. Thayer, A. Chem. & Eng. News. May 6, 2002, p 23-30. 16. Goedert, R.; Becker, R.; Clements, A.; Whittaker,T., III. J. Opt. Soc. Am. B. 1998, 15, 1442-62. 17. Powell, R. Chemical Process Review No. 21; Noyes Development Corp.: Park Ridge, NY, 1968. 18. Smisek, M ; Cemy, S. Active Carbon: Manufacture, Properties and Applications; Elsevier: Amsterdam, 1970. 19. Mattson, J.; Mark, H., Jr. Activated Carbon: Surface Chemistry and Adsorption from Solution; Marcel Dekker: New York, NY, 1971. 20. Cooney, D. Activated Charcoal: Antidotal and other Medial Uses, Drugs and Pharmaceutical Science; Marcel Dekker: 1980, Vol. 9. 21. private communicationfromCabot Corp. 22. Zlaczower, I. In reference 8; Chapter 11. 23. Gerspacher, M . In reference 8; Chapter 8.


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24. Didenko, Y.; Suslick, K. Nature 2002, 418, 394. 25. Bonard, J.; Stora, T.; Salvetat, J.; Maier, F.; Stockli, T.; Duschl, C.; Forro, L.; de Heer, W.; Chatelain, A. Adv. Mater. 1997, 9, 827-31. 26. Coughlin, R.; Azra, F.; Tan, R. In reference 1, p 44-54. 27. Steele, W.; Karl, R. In reference 1, p 55-60. 28. Walker, P.; Janov, J. In reference 1, p 107-115. 29. Kiselev, A. In reference 1, p 88-100.


Carbon Black Dispersions: Minimizing Particle Sizes by Control of

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