THE INFLUENCE OF OIL-IN-WATER EMULSIONS ON THE HYDRATION OF KERATIN

[摘要] A semi-permeable film is formed after evaporation of water from an oil-in-water emulsion. The emulsion may be so formulated that it becomes an adequate barrier to loss of water contained in callus, measured over a 16-hour period. The efficiency of this barrier depends on a certain minimum viscosity, the physical characteristics of the oil phase and the degree of hydrophilia of any adjuvants or secondary emulsifiers which may interfere with the formation of a continuous lipid film. Emulsifiers affect this barrier only as they change viscosity. Changes in the oil phase or the addition of hydrophilic adjuvants may produce an alteration of the barrier that is not directly proportional to any viscosity change. Hydrophilic adjuvants generally decrease barrier efficiency. Thus a preparation of high viscosity may form a barrier inferior to one that is less viscous. The foregoing would apply under conditions of low relative humidity where the callus loses water to the atmosphere. Passage of water vapor into callus at high relative humidities appears not to be influenced by the presence of an oil-in-water emulsion film or the type of film. Lipids presumably emulsified in keratin must be primarily in an oil-in-water emulsion, else the horn would not be able to exchange water as rapidly as it does under extreme conditions. If this is true, both water and solvent substances may remove lipid and emulsifier together, decreasing the total amount of water that the horn is able to bind, hence decreasing relative pliability. Certain types of oil-in-water emulsions are unique in that they show this water barrier characteristic at low relative humidities, maintaining it for an effective period, while permitting rapid diffusion of water at high humidities. This is a property not shown to any extent by water-in-oil emulsions or greases.