How non-ionic “electrically neutral” surfactants enhance electrical conductivity and ion stability in non-polar liquids

We show that it is possible to control the electrical conductivity of non-polar liquids such as kerosene using substances that are normally presumed to be non-dissociating and electrically neutral. This assumption is reflected even in the name “non-ionic surfactants”. These surfactants “solvate ions” in non-polar liquids by building protective shells around them, similar to the hydration layers of water around ions in aqueous solutions. The number of ions, and consequently the conductivity, correlates with amount of the solvating surfactant. This is a unique situation in which “solvation” controls the number of ions. It is exactly opposite to the situation in most aqueous systems for which the solvating agent (the water molecules) is in excess and the number of ions correlates instead with the amount of the dissociating agent. In order to determine the size of these “stericaly stabilized” ions we use a combination of conductivity and electroacoustic measurements. This approach was successfully used fifty years ago by Zana and Yeager to determine the size of hydrated ions in water. In the present case, these surfactants create anions and cations having quite different sizes, 30 and 1 nm, respectively.