A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes

Abstract

Liquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the ‘bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature. Indeed, aqueous suspensions of imogolite nanotubes, at low ionic strength, display the columnar liquid-crystal phase at volume fractions as low as ∼0.2%. Consequently, due to its low visco-elasticity, this columnar phase is easily aligned in an alternating current electric field, in contrast with usual columnar liquid-crystal phases. These findings should have important implications for the statistical physics of the suspensions of charged rods and could also be exploited in materials science to prepare ordered nanocomposites and in biophysics to better understand solutions of rod-like biopolymers.

Stability of Halloysite, Imogolite, and Boron Nitride Nanotubes in Solvent Media

“…Contrarily, the columnar phase, which can be seen in suspensions of other rod-like particles, was only observed at large volume fractions (10-70%) [68][69][70]. Meanwhile the columnar phase of INTs is presented at concentrations that are two orders of magnitude lower (Figure 3) [9]. the solution, and no precipitation was found for 24 h [64].…”

“…With this aim, this review will be focused on the colloidal stability of inorganic nanotubes, as well as on the most used strategies to prepare well-dispersed suspensions. In particular, these aspects will be investigated for halloysite nanotubes (HNTs) [8], imogolite nanotubes (INTs) [9], and boron nitride nanotubes (BNNTs) [10].…”

“…Their structure, proposed by Cradwick in 1972, is very similar to halloysite, namely a layer of orthosilicate tetrahedra overlapping a layer with an aluminum in a dioctahedral configuration [36]. INTs are considered the clay counterpart of carbon nanotubes, and they are very similar if dimensions, aspect ratios, and rigidity are considered [9]. Moreover, imogolite nanotubes are easily synthesized using hydrothermal techniques, without purification steps to do post-synthesis, and they form stable colloidal suspensions in aqueous solvents [34,37].…”

“…On the other hand, Paineau et al [9] firstly observed that INTs show a liquid-crystal phase, columnar in particular, at low concentrations (≈0.3%) with low visco-elasticity and that is aligned under an electric field.…”

M-Polynomials and Topological Indices of Titania Nanotubes

“…In addition, a comparison between three-and six-layered titania nanotubes can be launched with the help of careful analysis of the above results. The methodology described above can be extended to emerging types of neontubes: aluminosilicate/aluminugerminate [20,[24][25][26]. …”