The effects of grafted carboxyl groups on the elastic properties of single-walled boron nitride nanotubes

The molecular dynamics method is used to investigate the effect of grafted carboxyl groups on the elastic properties of (5,5) and (6,6) armchair and (9,0) and (10,0) zigzag single-walled boron nitride nanotubes (SWBNNTs). The results show that the Young's moduli of (5,5) and (6,6) armchair and (9,0) and (10,0) zigzag SWBNNTs with no grafts are 920 and 884 GPa and 780 and 767 GPa, respectively. When the SWBNNTs are grafted by carboxylic functional groups, the Young's moduli all decrease. Thereamong, the fall for the zigzag SWBNNTs is larger than that for the armchair SWBNNTs, but their Young's moduli show few varieties as the graft quantity increases. The armchair SWBNNTs behave somewhat differently. Their moduli are sensitive to the graft quantity: an increase in grafts causes greater fluctuations around some intermediate value in the moduli. These results indicate that the effects of grafted carboxyl groups on the elastic properties of SWBNNTs are related to their chiral angle. The smaller the chiral angle, the greater the influence of the grafts but the lesser the influence of graft quantity on the grafted SWBNNTs. The grafted zigzag SWBNNTs have more stable elastic properties than the grafted armchair SWBNNTs. This phenomenon can be best analyzed according to the law of the isoline structure of deformation electron density and bondlength variation of SWBNNTs with different graft quantities. The average circumferential bond-length changes for grafted armchair SWBNNTs and the average axial bond-length changes for grafted zigzag SWBNNTs have good corresponding relations with the changes in their Young's moduli. Copyright © 2010 American Scientific Publishers All rights reserved.