Surface Potentials of Water and Organic Solvents

The surface potential of water, x , as any other surface potential, is not measurable. Its probable value is inferred from indirect observations. Such a potential difference has been postulated because the tetrahedral charge 

Many attempts to estimate x on the basis of different nonthermody-namic assumptions have shown that the value of this potential is positive and that it is comparatively small. According to subsequent estimates by Frumkin, Randles, and Trasatti x is equal to +0.1, +0.08 0.06, and +0.13 V, respectively. Dynamic experiments have confirmed this order of value. The time of establishing the equilibrium value has been found to be about 3 ms. 

The impossibility of x being equal to about 1 V, as suggested by Kamieifki, has been demonstrated by Frumkin on the basis of a discussion of the real energies of hydration. Estimates from the variation in the solution surface potential with electrolyte molarity have yielded the value of +0.025 0.010 V.21 For methanol, the same method results in a value of -0.09 V.146 Later the authors of that investigation stated that both estimated values should be understood as the lower limits of surface potentials of water and methanol.  

Recent molecular dynamics studies of properties of the water surface have led to predictions of the surface potential of water that differ not only in magnitude but also in sign. The main problem is connected with the difficulty of proper definition of the surface potential of a real polar 

The published experimental estimates of the surface potentials of various organic solvents have been derived mainly from the data on the real, asi, and chemical, gSi, energies of solvation of ions  

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