whereas MWNT consists of a number of concentric SWNT.Both SWNT and MWNT are closed at the ends by dome-shaped caps.The concentric SWNTs inside an MWNT are also end-capped.The diameter of an SWNT is typically between 1 and 1.4 nm and its length is between 50 and 100 um.The specific surface area of an SWNT is 1315 m2/g,and is independent of its diameter [15].The outer diameter of an MWNT is between 1.4 and 100 nm. The separation between the concentric SWNT cylinders in an MWNT is about 3.45 A,which is slightly greater than the distance between the graphite layers in a graphite crystal.The specific surface area of an MWNT depends on the number of walls.For example,the specific surface area of a double-walled nanotube is between 700 and 800 m2/g and that of a 10-walled nanotube is about 200 m2/g [15]. The structure of an SWNT depends on how the graphite sheets is rolled up and is characterized by its chirality or helicity,which is defined by the chiral angle and the chiral vector(Figure 8.5).The chiral vector is written as Ch na1 ma2, (8.1) Zigzag direction (0,0) (3,0) (4,0) (6,0) (8,0) (9,0) (1,1) Ch (8,1) (2,2) (4,2) (5,2) (7,2) (8,2) (3,3) (6,3) a2 (4,4) (74) (5,5) Armchair direction FIGURE 8.5 Chiral vector and chiral angle.(From Govindaraj,A.and Rao,C.N.R., The Chemistry of Nanomaterials,Vol.1,C.N.R.Rao,A.Muller,and A.K.Cheetham, eds.,Wiley-VCH,KGaA,Germany,2004.With permission.) 2007 by Taylor&Francis Group.LLC.whereas MWNT consists of a number of concentric SWNT. Both SWNT and MWNT are closed at the ends by dome-shaped caps. The concentric SWNTs inside an MWNT are also end-capped. The diameter of an SWNT is typically between 1 and 1.4 nm and its length is between 50 and 100 mm. The specific surface area of an SWNT is 1315 m2 =g, and is independent of its diameter [15]. The outer diameter of an MWNT is between 1.4 and 100 nm. The separation between the concentric SWNT cylinders in an MWNT is about 3.45 A8, which is slightly greater than the distance between the graphite layers in a graphite crystal. The specific surface area of an MWNT depends on the number of walls. For example, the specific surface area of a double-walled nanotube is between 700 and 800 m2 =g and that of a 10-walled nanotube is about 200 m2 =g [15]. The structure of an SWNT depends on how the graphite sheets is rolled up and is characterized by its chirality or helicity, which is defined by the chiral angle and the chiral vector (Figure 8.5). The chiral vector is written as Ch ¼ na1 þ ma2, (8:1) Zigzag direction (0,0) (1,1) Ch (3,0) (2,2) a1 a2 (3,3) (4,4) (5,5) Armchair direction (7,4) (6,3) (4,2) (5,2) (7,2) (8,2) (4,0) θ (6,0) (8,0) (8,1) (9,0) FIGURE 8.5 Chiral vector and chiral angle. (From Govindaraj, A. and Rao, C.N.R., The Chemistry of Nanomaterials, Vol. 1, C.N.R. Rao, A. Mu¨ller, and A.K. Cheetham, eds., Wiley-VCH, KGaA, Germany, 2004. With permission.)
2007 by Taylor & Francis Group, LLC