Chapter 8: Chemotactic Droplets Serving as ‘Chemo-Taxis’

Chemotaxis is a natural way for cells and organisms to perform oriented movement in a chemical gradient. Positive chemotaxis occurs if the movement is in the direction of increasing concentration. If the movement is in the opposite direction, the chemotaxis is called negative. The goal of this chapter is to describe non-biological positive chemotactic movements of liquid robots in the form of liquid droplets in the concentration gradient of different chemical signal molecules. The movement mechanism is based on the Marangoni effect acting on decanol droplets in an aqueous environment. It is shown that the chemotactic droplets cannot only move by themselves, but also serve as transporters for dissolved chemically reactive payloads or even small physical objects, thus the term ‘chemo-taxi’. In future, artificial chemotaxis could be used as a transport mechanism for micro-scale devices and chemicals.