Aggregation of Synthetic Chrysotile Nanotubes in the Bulk and in Solution Probed by Nitrogen Adsorption and Viscosity Measurements

Abstract

Chrysotile nanotubes (ChNTs) were synthesized under hydrothermal conditions. The shape and size of individual ChNTs were examined by transmission electron microscopy (TEM). Specific surface area (SSA) of nanotubes surface treated with a silane coupling agent and of pristine nanotubes in the bulk was determined by BET analysis of N 2 adsorption at 77 K. The theoretical SSA of a single nanotube and of nanotubes organized in a bundle was calculated as a function of nanotube geometrical parameters and the bundle size, that is, number of nanotubes in the bundle. A comparison of experimental and theoretically calculated SSA values indicated that nanotubes form bundles in the bulk. The characteristic bundle size in the bulk was estimated. The tendency of ChNTs to form bundles was also investigated in polar (ethanol) and nonpolar (xylene) solvents by measuring the complex viscosity behavior of the corresponding colloidal solutions. Viscosity measurements showed that nanotubes form bundles and that they are larger, consisting of more nanotubes, in nonpolar xylene than in polar ethanol. The tendency of ChNTs to aggregate in the bulk and in the solution was reduced by surface treatment of nanotubes with a silane coupling agent.

Structural features of natural and acids modified chrysotile nanotubes

“…9 [10]. The chrysotile nanotubes obtained by synthesis method are characterized by the 1 average outer diameter 14 nm and the average inner diameter of the channel 3 nm [10]. But 2 these synthetic tubes were shorter (from 10 nm to 600 nm) than the raw ones.…”

“…Therefore, in this case only partial (fragmentary) leaching of 8 octahedral layer can be noted and thus the crystal structure is preserved. 9 [10]. The chrysotile nanotubes obtained by synthesis method are characterized by the 1 average outer diameter 14 nm and the average inner diameter of the channel 3 nm [10].…”

“…A lot of inorganic nanotubes have been already synthesized with target to use in 19 nanoelectronics as a dielectric matrix [8]. Considerable recent attention has been focused on 20 natural chrysotile, synthetic chrysotile nanotubes and nanofibrous silica produced from 21 chrysotile [9,10]. 22 It is customary to use chrysolite in industry for asbestos-cement production (pipes and sheets), 23 thermal insulation, filtering devices, and friction material for brakes [11,12].…”

“…The nanofibrous silica with the high surface area was extracted from 14 chrysotile by the acid-leaching method [24,25]. Recently, chrysotile nanotubes were also 15 synthesized under hydrothermal conditions [9,10,26]. 16 The comprehensive characteristics of structural features and physicochemical properties of 17 chrysotile nanotubes can promote their potential applications in nanotechnologies.…”

“…It can be assumed that the micropores may appear as a consequence of 9 destruction and plastic dislocations of the chrysotile sheets under influence of acid treatment. 10 The surface areas and the pore volumes of the samples calculated using the BJH method are 11 presented in Table 2. The cumulative pore volumes of the chrysotile mesopores before and 12 after acids treatment evaluated from adsorption curves were 0.014 and 0.…”