Origin of the Strain Energy Minimum in Imogolite Nanotubes

Abstract

We have systematically analyzed the structure of imogolite and their energetics, to understand the physics governing control over imogolite nanotube diameter and strain energy. In this work, we have presented evidence that the arrangements of inner and outer hydroxyl (OH) groups, that is hydrogen bond (HB) networks, play an important role in the formation of imogolite nanotubes and their structural stability. The outer HB significantly affects the Al−O distances and generates two different structures. Even though the relaxation of inner and outer Al−O and Si−O bond distances is the driving force for tubular imogolite formation, we show that the origin of the strain energy minimum, that is high monodispersity of diameter in imogolite nanotubes, is the inner HB networks. The preference for zigzag chirality and the formation mechanism of tubular imogolite also can be understood based on HB networks. Therefore, we present that a comprehensive understanding of the origin of high monodispersity of diameter and the preference for zigzag chirality in imogolite nanotubes provide useful insight into the researches of technical applications of imogolite nanotubes.

Clay Mineral Nanotubes: Stability, Structure and Properties

“…Although the same methodology (DFT), functional (PBE), local basis and program (SIESTA) had been used as the previous discussed work (Zhao et al, 2009), the strain energy curve profile and minimum for imogolite are different. Lee et al (2011) have found a minimum at (8,0) and the strain energy curve does not present any local minimum, in contrast to Zhao et al (2009) that found the most stable structure at (9,0) and a local minimum at (12,0). Demichelis et al ( 2010) also contributed to the imogolite energy minimum topic.…”

“…Moreover, the presence of hydrogen bonds chains in the inner wall of the zigzag tubes allows stabilization of the curled structure in comparison to the armchair one. Lee et al (2011) also presented evidences that the unique arrangement of inner silanol groups (Si-OH) and the hydrogen network are the origin of the strain energy minimum and are the reason for preference of the zigzag chirality. According to those authors, depending on the rolling direction, inner silanol OH groups produce distinct hydrogen bond (HB) networks, e.g., for zigzag tubes occurs disk inner HB because inner OH groups are aligned with zigzag like rolling direction in parallel and helix-like inner HB networks occurs to armchair.…”

“…Several theoretical studies (Tamura & Kawamura, 2002;Konduri et al, 2006;Alvarez-Ramirez, 2007;Guimaraes et al, 2007;Zhao et al, 2009;Demichelis et al, 2010;Lee et al, 2011) using different methodologies indicated that there is clearly a minimum in the strain energy curve of the imogolite. However, the minimum value is still a matter of controversy.…”

“…Recently, first-principles calculations based on DFT have also been performed in order to study the origin of the strain energy minimum in imogolite NTs (Lee et al, 2011). Although the same methodology (DFT), functional (PBE), local basis and program (SIESTA) had been used as the previous discussed work (Zhao et al, 2009), the strain energy curve profile and minimum for imogolite are different.…”

“…The zigzag NTs can effectively construct inner HB networks. In order to evaluate the zigzag preference, Lee et al (2011) have investigated the structural relaxation of hydrogen saturated curved gibbsite-like imogolite, i.e., a piece of gibbsite like with armchair configuration. The obtained results have shown the curved gibbsite-like tubes spontaneously change the chirality from armchair to zigzag by shortening inner HB distances and changing the rolling direction.…”