Energy Modeling of Competition Between Tubular and Platy Morphologies of Chrysotile and Halloysite Layers

Abstract

The present study considered the problem of halloysite nanoscroll synthesis by energy modeling of the formation of chrysotile and halloysite particles. The main aim of the study was to reveal an energy preference between scrolled and platy morphologies of the particles. Both hydrosilicates possess the ability to scroll spontaneously but relatively facile hydrothermal synthesis of the nanoscrolls is available only to the former, whereas halloysite forms mainly plates under the same conditions. This issue was investigated by a phenomenological energy model, taking into account: (1) strain energy due to the size difference between metal oxide and silica sheets; (2) surface-energy difference on the opposite sides of the layer; and (3) adhesion energy. Calculations showed that the halloysite layer had a significant scrolling potential due to the first energy component, but the surface-energy difference acted in the opposite direction and tried to unbend the layer. In contrast, these two actions were co-directional in chrysotile layers. In both cases, the formation of multi-layered plates became more energy favorable when the specific surface energy of the edges decreased. In the range 0.5–3 J/m2 for the specific surface energy, only halloysite layers showed an energy preference for platy particles over nanoscrolls, especially at small layer sizes. Certain processes, such as hydration, could reduce the corresponding specific surface energy value and, as a result, could stabilize the platy morphology of halloysite at the earliest stages of particle growth under hydrothermal conditions.

Nanostructure of serpentinisation products: Importance for water transport and low-temperature alteration

“…is not expected to be significantly different for brucite and lizardite in the coating mixture (Malvoisin and Brunet, 2014). However, is 1.5 J/m 2 for the (111) SiO2 surface and 0.05 J/m 2 for the (001) Mg(OH)2 surface (Churakov et al, 2004;Krasilin, 2020). These data indicates that the surface energy of lizardite could be approximately one order of magnitude higher than for brucite.…”

The influence of edge specific surface energy on the direction of hydrosilicate layers scrolling

“…( 1)). The case of a multiwalled-nanoscroll is compared with that of a multilayered plate, for which the energy gap between them would be lower [42]. Depending on the σ hk0 /σ h k 0 pair, the energy effect could differ on approximately 400 J/mol, whereas the preferable spiral length L 1 almost did not change.…”

“…1 Structural data was adopted from [27] and visualized by VESTA software [50] Only Mg-O and Si-O bonds were taken into account having bond energies E Mg-O = 401 ± 13 kJ/mol [49] and E Si-O = 444 ± 18 kJ/mol [48], respectively. Some of the (hk0) planes may intersect hydrogen bonds, however, their estimated energy (5.2 kJ/mol [42]) was almost two orders of magnitude less than those of Mg-O and Si-O bonds. In this regard, hydrogen bonds were omitted during the calculation.…”

“…The present study has attempted to investigate the issue with scrolling direction of hydrosilicate layers from an energy modeling [37][38][39][40][41][42] perspective. Recent developments in the field of phenomenological modeling of scrolling [42] have revealed a crucial role for the specific surface energy σ of the hydrosilicate layer edges in the choice between platy and scrolled particle shape. That study, however, operated with arbitrary range of edge σ values.…”

Young’s modulus of phyllosilicate nanoscrolls measured by the AFM and by the in-situ TEM indentation

“…Phyllosilicates with chrysotile, pecoraite, halloysite structure, as well as some others [1] roll up into long nanotubes and nanoscrolls with outer and inner diameters being in the range of 20 − 200 nm and 4 − 30 nm, respectively. The driving forces of the phyllosilicate layers scrolling are the surface structure differences and the crystal lattice mismatches between the metal-oxygen (octahedral) and silicon-oxygen (tetrahedral) sheets [2]. A similar mechanism underlies the method of 3D micro-and nanostructures production [3], in which a strained semiconductor film is separated from the substrate using a sacrificial layer, and then scrolled to compensate the strains.…”