Aqueous suspensions of steroid nanotubules: Structural and rheological characterizations

It has been known that lithocholic acid self-assembles in highly alkaline aqueous dispersions. By a combination of cryogenic-temperature transmission electron microscopy and small-angle neutron and X-ray scattering, we were able to characterize the long single-walled nanotubules that are formed in the system. We have found that the nanotubules appear quite monodisperse with cross sections of 52 nm outer diameter and an internal cylindrical cavity of 49 nm diameter. Such a steroid introduces a new class of tubule-forming systems with cavity dimensions in a not previously reported nanoscale range. The flowing properties of the lithocholate suspensions are analyzed, and it is concluded that the uniform nanotubules are interacting moderately in the suspensions. As these nanotubes are fairly insensitive to the presence of salts, they are potentially good candidates for metallization and mineralization templates.