Investigations into precipitation membrane growth

Abstract

In nature, hollow precipitation tubes form around deep sea hydrothermal vents and generate an electric potential across the material membrane. These structures are of significant scientific interest due to their possible connection to the origins of life on Earth, and synthetic precipitation membrane structures have been created in the laboratory to study their growth. This paper reports on the formation of metal hydroxide precipitation membranes within a microfluidic device designed to allow for the measurement of the electric potential across the flow channel during material formation. Using this device, the electric potential and growth curves were measured for nickel hydroxide, iron hydroxide, and cobalt hydroxide precipitation membranes. Based on these experiments, it was hypothesized that the application of an electric potential in opposition to the generated potential would reduce the growth rate of the membranes, and this hypothesis was experimentally verified. The results of this work discuss that the membranes formed are likely selectively permeable to a diffusive positive ion, possibly H+, which is responsible for controlling the growth rates of the material. Additional experiments, including direct electrical measurements of the membrane itself during growth, measurement of the pH within the flow channel, and material characterization after removal from the device, are proposed to further explore the growth of precipitation membranes.