1. Could you explain the significance of your article to the non-specialist?

In nature, very diverse processes create astonishingly similar tubular structures. Examples include black smokers at hydrothermal vents, silica tubes in setting cement, soda-straw stalactites in caves, and biological structures such as the outer skeleton of certain algae.

Our work aims to establish and understand a lab-scale model by using the, seemingly simple, precipitation reaction between sodium silicate and copper sulfate.

This Article reports a surprising mode of rapid tube growth that is guided and templated by rising gas bubbles. Our experiments will help to understand tube morphogenesis in general and possibly suggest unconventional strategies for the fabrication of novel materials.

2. What has motivated you to conduct this work?

Our research team also investigates self-organization in corrosion systems. Blistering corrosion, which occurs at very high relative humidity, induces the growth of upright, millimeter-scale rust tubes. While we are intrigued by this phenomenon, this work is hampered by the extremely slow growth rate of these rust tubes (less than 1 mm/month).

During a Gordon research conference in Oxford, I learned about Julyan Cartwright's (Granada, Spain) work on "silica gardens", who was using Mach-Zehnder interferometry to quantify the flow fields in this system. 

Later, I learned about the colorful history of silica gardens which were once believed to be pre-biotic life forms. Moreover, I learned about the intriguing hierarchical nano-to-centimeter scale structure of the tube material and their potential as catalysts. I also began to understand that very different tube-forming systems share certain, poorly understood principles.

All of this enticed us to develop a reliable experimental model for this phenomenon and systematically explore different modes of tube growth in our system.

3. Where do you see this work developing in the future?

We still understand very little about this system. The immediate challenge is to learn as much as possible from analyzing the readily observable, macroscopic behavior.

These studies will reveal the physics behind different growth regimes and identify the dynamical instabilities that govern growth-mode transitions. Important long-term challenges include the use of this knowledge for the active design of the samples' microstructure, the fabrication of tube arrays, and perhaps the chemical patterning of the resulting materials.

4. Are there any particular challenges facing future research in this area?

Conventional equilibrium measurements will not cut to the heart of this non-equilibrium system. Also reaction-diffusion-flow coupling plays an essential role. These complications make the system interesting.