Formation of Regular Wormlike Patterns by Dewetting Aqueous Dispersions of Halloysite Nanotubes

The wormlike micropatterns were elaborated by drying halloysite clay nanotube dispersions placed between two horizontal glass slides. This 0.1–0.2 mm thick confined space induces the fractal self-assembly of charged nanotubes governed by water evaporation and flow directions. The wriggled stripe clay patterns were formed both on the upper and bottom glass surfaces with width, height, and stripe spacing controlled by halloysite concentrations, space height, drying time, and temperature in the range of 20–80 °C. After separating the slides, the pattern was divided into two identical fractal clay surfaces. Birefringence in the stripes demonstrated the nanotube oriented domains with 50–100 μm length. A model for the pattern formation is proposed relating this phenomenon with the colloidal self-assembly and coffee-ring formation mechanisms. These solid micropatterns can be transferred on polydimethylsiloxane stamps for further polymer imprinting. The technique is simple and scalable and uses water-based natural clay materials, allowing for green chemistry surface processing.