Visualization of Charge-Carrier Propagation in Water

Abstract

The electrical properties of water in the region between parallel electrodes were investigated using pH indicator dyes. Different pH values corresponded to different colors, which could be registered by a video camera. Imposition of electrical current was able to produce zones of constant pH around, and well beyond each electrode: extremely low pH around the positive electrode and extremely high pH around the negative electrode. The border between alkaline and acid zones was jagged and separated by only a narrow layer of water with neutral pH. When the water was replaced by various salt solutions, similar zones were observed. Again, passage of current produced large zones of extreme pH values near and beyond each electrode. Alkaline zones appeared to propagate from the negative to the positive electrode in narrow channels through the neutral solution. When the power supply was disconnected from the electrodes and replaced by a resistive load, a potential difference was registered, and current flowed through the resistor for some period of time. Hence, the acid and alkaline zones appear to carry opposite charges throughout their volume.