Using surface tension data to predict differences in surface and bulk concentrations of nonelectrolytes in water

Recently, we developed a quantitative interpretation of surface tension increments (STI) of salts, acids, and bases in terms of the solute (or salt ion) partitioning model (SPM). Here, we obtain an analogous SPM-based interpretation of surface tension increments of nonelectrolytes, which yields local-bulk partition coefficients (Kp) quantifying the accumulation or exclusion of these solutes in the local region near the air−water surface, and the amount of water per unit area of that region (b1σ). Sucrose exhibits the largest positive STI (approximately 1.4 ergs cm−2 Osm−1). Assuming that Kp = 0 for sucrose (i.e., that it is completely excluded from the surface of water), these STI provide a minimum estimate of b1σ of 0.20 H2O/A2, or a minimum thickness of the surface region of approximately two layers of water at bulk density. This is the same value as obtained previously from analysis of surface tension and hydrocarbon solubility increments of Na2SO4 and also for the interaction of glycine betaine with a...