ELECTROLYTES AND EMULSION STABILITY 187 Ethoxylate adsorption and interfacial coverage reach a maximum with a specific, as determined by ethylene oxide content, hydration energy above or below the limiting optimal hydration energy reduced adsorption results. The El5, El0, and E5 ethoxylates have hydration energies determined to a large extent by their ethylene oxide content. The pres- ence of added sodium, potassium, or calcium chloride reduces this hydration energy. However, in the case of the El5, El0, and E5 ethoxylates, their ethylene oxide content may be--by correlation of the variations in surface tension observed at the C.M.C. in the presence of electrolyte--greater than that required for optimal adsorption. It is also suggested that the reduction of the greater than optimal hydration energy through the addition of electrolyte can be related, in specific in- stances, to particle size reductions. Added electrolyte reduced the hydration energy of the El5, El0, and E5 ethoxylates by disrupting ethoxylate-water molecule interactions. However, in the case of formulations containing the El5, El0, and E5 ethoxylates, the hydra- tion energy is effectively reduced by electrolytes to the point of optimal stability. It is suggested that, since the ethylene oxide content of the E5 product is less than that of El0 or El5, smaller quantities of electrolyte are required to induce parameter variations associated with optimum stability. However, at electrolyte content greater than the 10% experimental limits the variations can be associated with still better emulsion stability in the case of the El5 and El0 products instead of deterioration as might occur with the E5 ethoxylate. Examination of the experimental data indicates that the surface parameter variations caused by sodium or potassium chloride were similar but of different magnitude than those brought about by the addition of calcium chloride. The pH's of formulations with El5, El0, and E5 ethoxylates and calcium chloride are lower than those of other emulsions. The ions released by the hydrolysis of calcium chloride result in acidic emulsion conditions. It has been claimed that aqueous solutions of inorganic acids have lower surface tensions than water (11, 12). This leads to the conclusion that the proton is adsorbed at the surface, a result which conflicts with that of other investigations (13). However, the proton adsorption theories do not satisfy the experimental results of this paper. Instead, it is postulated that the protons released through hydrolysis of calcium chloride are not strongly adsorbed. If they were adsorbed, competition for space at the emulsion interface might occur. In the presence of excess protons, the ethoxylate may not be adsorbed in those instances where interfacial coverage was en-

188 JOURNAL OF THE SOCIETY OP COSMETIC CHEMISTS hahted by added electrolyte to as great an extent as is observed with electrolytes which do not release excess hydrogen ions. Even though emulsion and surface parameter variations indicate increased emulsion stability with the El5, El0, and E5 ethoxylates in the presence of added electrolyte, the nature of the variations are such that formulations which contain sodium or potassium chloride may have greater long range emulsion stability than those containing calcium chloride. In this instance, the hydration of the polyvalent calcium ion induced parameter variations which are associated with diminished stability relative to those created by potassium or sodium chloride. SUMMARY The measurable effect of added electrolyte on emulsions containing ethylene oxide-fatty alcohol derivatives as primary emulsifiers depends on several factors and their interrelation. 1. The interaction of the electrolyte with the water molecules is an important factor. Added electrolyte disrupts ethoxylate-water mole- cule interactions. The presence of ions causes the water molecules to be drawn toward themselves. Hydrogen bonding among neighboring water molecules and hydration of the ethylene oxide groups of the ethoxylate molecules are inhibited. Consequently, the effective hydra- tion energy and solubility of the ethoxylate are diminished. 2. Ethoxylate hydration energy will help determine the extent of adsorption, particle size, C.M.C., and surface tension at the C.M.C. The values of these factors, as determined by inherent or electrolyte- induced ethoxylate hydration energy, play a decisive role in the emulsion's resistance to coalescence. By applying the numerical values for the above factors to Gibbs' adsorption isotherm and Stokes' cream- ing and sedimentation equation, the relative stability of the experi- mental formulas to coalescence can be predicted. 3. The quantity of electrolyte introduced into the experimental emulsions containing the El5, El0, and E5 ethoxylates determines emulsion stability. The presence of added electrolyte will reduce the hydration energy of the ethoxylate in a direct quantitative relationship. In those instances in which hydration energy is too great to be con- sistent with maximum interfacial adsorption, interfacial coverage (and as a consequence emulsion stability) increases with increasing amounts of electrolyte. 4. The nature of the electrolyte is also an important factor in pro- jected emulsion stability. The inclusion of sodium or potassium chloride