pubs.acs.org/Langmuir © 2010 American Chemical Society
Single-Walled Carbon Nanotube/Lyotropic Liquid Crystal Hybrid Materials Fabricated by a Phase Separation Method in the Presence of Polyelectrolyte Xia Xin,*,† Hongguang Li,† Ewelina Kalwarczyk,† Anna Kelm,‡ Marcin Fia lkowski,† Ewa Gorecka,§ Damian Pociecha,§ and Robert Ho lyst*,†,^ /
/
† Department III, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland, ‡College of Inter-Faculty Individual Studies in Mathematics and Natural Sciences, _ University of Warsaw, Al. Zwirki i Wigury 93, 02-089 Warsaw, Poland, §Department of Chemistry, _ University of Warsaw, Al. Zwirki i Wigury 101, 02-089 Warsaw, Poland, and ^ Department of Mathematics and Natural Sciences, College of Science, Cardinal Stefan Wyszynski University, Dewajtis 5, 01-815 Warsaw, Poland
Received December 5, 2009. Revised Manuscript Received April 12, 2010 We present a detailed study on the incorporation of single-walled carbon nanotubes (SWNTs) into lyotropic liquid crystals (LLC) by phase separation in the presence of polyelectrolytes. Two cases were studied in this work: (i) incorporation of SWNTs into the LLC phase formed by an anionic surfactant sodium dodecyl sulfate (SDS) in the presence of an anionic polyelectrolyte poly(sodium styrenesulfonate) (PSS); (ii) incorporation of SWNTs into the LLC phase formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB) in the presence of a cationic polyelectrolyte poly(diallydimethylammonium chloride) (PDADMAC). The SWNTs/LLC composites were characterized by polarized optical microscopy (POM) observations and small-angle X-ray scattering (SAXS) measurements. In both systems, the surfactant phase was condensed into a hexagonal lattice by the polyelectrolyte within the investigated concentration range. Several factors that can influence the property of SWNTs/LLC composite were examined, including concentration of surfactants and polyelectrolytes and temperature. Aggregated SWNTs were not observed, indicating that SWNTs were well dispersed in the LLC phases. SAXS measurements showed the lattice parameter of the host LLC phase changed upon varying the mixing ratio of polyelectrolyte to ionic surfactant. The SWNTs/LLC hybrids showed considerable stability against temperature rise in both systems, and desorption of surfactant from SWNTs was not observed at higher temperature.
Introduction Carbon nanotubes, especially single-walled carbon nanotubes (SWNTs), are among the most fascinating nanomaterials which have received increasing attention during the past decade. SWNTs show promise for a wide range of applications due to a combination of their unusual structural, mechanical, and electronic properties.1-3 Induced by van der Waals attraction between adjacent tubes which have extremely high aspect ratios, the asproduced raw SWNTs usually exist as ropes rather than single tubes, making it rather difficult to manipulate these interesting nanomaterials. A dispersion of SWNTs in a solution is thus a crucial requirement in realizing their full potential applications. In *To whom correspondence should be addressed. E-mail:
[email protected]. edu.pl (R.H.);
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Published on Web 04/22/2010
DOI: 10.1021/la101032d
8821
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the help of different kinds of surfactants and conjugated polymers,10 amphiphilic block copolymers,12 polyelectrolytes,24 and biopolymers.25 Surfactant or polymer-wrapped SWNTs can be effectively dispersed in a solvent without damaging SWNTs, up to a level of even single tube. Another problem that needs to be solved is the effective alignment of SWNTs. SWNTs are exceptionally anisotropic particles, with diameters on the order of nanometers but lengths ranging from micrometers to centimeters;27 they display most of their expected properties along the tube axis. The uniform alignment is therefore a crucial condition in most of the fascinating applications proposed to SWNTs such as innovative composite materials,15 solar cells,28 and sensors.29 Unfortunately, in SWNTs dispersions obtained with the help of surfactants or polymers, the tubes are randomly oriented. Thus, to utilize the full potential of SWNTs in diverse applications, one has to induce both the exfoliation of the bundles of SWNTs into individual tubes and subsequent tube alignment.30-33 In recent years, considerable attention has also been paid to the alignment of nanotubes by using lyotropic liquid crystals (LLC).34-41 With both fluidity and long-range order, LLC represents an ideal host to align CNTs. Dispersion of CNTs in LLC provides us a cheap, simple, versatile, and effective means of controlling nanotube orientation at macroscopic scale and at high CNT concentration, with no fundamental restrictions on nanotube type.42 In this case SWNTs dispersion is obtained first under sonication with the help of a surfactant, typically nonionic one such as Triton X-10041 or n-dodecylhexaoxyethene monoether (C12E6).43 Then more surfactant, either of the same type or different, is added to induce the formation of LLC. Since the viscosity of LLC is usually high at room temperature, a heating process is normally applied which may destroy the SWNTs/LLC composites due to the desorption of the nonionic surfactant at higher temperature. Recently, we have shown that the heating process can be avoided and SWNTs/LLC composites can be fabricated at room temperature via a phase separation of nonionic surfactant in the presence of a nonionic polymer such as poly(ethylene glycol) (PEG). In the present work, we report a detailed study of incorporation of SWNTs into LLC formed by ionic surfactants in the presence of polyelectrolytes. Our purpose is not only to illustrate and expand the phase separation method (27) Saito, R.; Dresselhaus, M. S.; Dresselhaus, G. Physical Properties of Carbon Nanotubes; Imperial College Press: London, 1998. (28) Guldi, D.; Rahman, G. M. A.; Prato, M.; Jux, N.; Qin, S.; Ford, W. Angew. Chem., Int. Ed. 2005, 44, 2015. (29) Modi, A.; Koratkar, N.; Lass, E.; Wei, B.; Ajayan, P. M. Nature 2003, 424, 171. (30) Casavant, M.; Walters, D.; Schmidt, J.; Smalley, R. J. Appl. Phys. 2003, 93, 2153. (31) Fischer, J. E.; Zhou, W.; Vavro, J.; Llaguno, C.; Guthy, C.; Haggenmueller, R.; Casavant, M. J.; Walters, D. E.; Smalley, R. E. J. Appl. Phys. 2003, 93, 2157. (32) Kamat, P. V.; Thomas, K. G.; Barazzouk, S.; Girishkumar, G.; Vinodgopal, K.; Meisel, D. J. Am. Chem. Soc. 2004, 126, 10757. (33) Nativ-Roth, E.; Yerushalmi-Rozen, R.; Regev, O. Small 2008, 4, 1459. (34) Lagerwall, J.; Scalia, G.; Haluska, M.; Dettlaff-Weglikowska, U.; Roth, S.; Giesselmann, F. Adv. Mater. 2007, 19, 359–364. (35) Badaire, S.; Zakri, C.; Maugey, M.; Derre, A.; Barisci, J. N.; Wallace, G. G.; Poulin, P. Adv. Mater. 2005, 17, 1673. (36) Song, W.; Kinloch, I. A.; Windle, A. H. Science 2003, 302, 1363. (37) Davis, V. A.; Ericson, L. M.; Parra-Vasquez, A. N. G.; Fan, H.; Wang, Y.; Prieto, V.; Longoria, J. A.; Ramesh, S.; Saini, R. K.; Kittrell, C.; Billups, W. E.; Adams, W. W.; Hauge, R. H.; Smalley, R. E.; Pasquali, M. Macromolecules 2004, 37, 154. (38) Dierking, I.; Scalia, G.; Morales, P.; LeClere, D. Adv. Mater. 2004, 16, 865. (39) Dierking, I.; Scalia, G.; Morales, P. J. Appl. Phys. 2005, 97, 044309. (40) Song, W. H.; Windle, A. H. Macromolecules 2005, 38, 6181. (41) Weiss, V.; Thiruvengadathan, R.; Regev, O. Langmuir 2006, 22, 854. (42) Lagerwall, J. P. F.; Scalia, G. J. Mater. Chem. 2008, 18, 2890. (43) Xin, X.; Li, H. G.; Wieczorek, S. A.; Szymborski, T.; Kalwarczyk, E.; Ziebacz, N.; Gorecka, E.; Pociecha, D.; Holyst, R. Langmuir 2010, 26, 3562.
8822 DOI: 10.1021/la101032d
Xin et al. Scheme 1. Illustration of the Phase Separation Method Used To Incorporate SWNTs into the LLC Matrix: (i) Sonication (43-45 kHz, 60 W, 2 h); (ii) Sedimentation (2 weeks); (iii) Homogenization (Hand-Shaking or Stirring); (iv) Phase Equilibration (30 C)
to ionic systems. Here we improve the stability of SWNTs/LLC hybrid materials against temperature increase by replacing nonionic surfactant with ionic ones, which can have big advantages in practical applications where the temperature is above room temperature.
Experimental Section Chemicals and Materials. SWNTs, with a diameter
