Strength of Emulsifier Films at Liquid-Liquid Interfaces

Abstract

Mass., AND RANDOLPH J. OWEX, The E. L. Patch Company, Stoneham, hIass. N A PREI'IOUS paper (7i t h e e a r l i e r investigations I on the formation of films of emulsifiers a t liquid-liquid interfaces and a simple method of forming such films were des c r i b e d . Qualitative informat i o n was given on the characteristics and speed of formation of films which appeared a t interfaces between aqueous solutions of eight different emulsifiers and four different oils.In this paper a method of m a king quantitative measurements of the strength of coher-A method is described for making quantitatice measurements of the strength of coherent films at the interface between emulsijier solutions and various oils. Data are given for the first time on the strength of such films and their changes on standing. These data are interpreted f r o m the point of view of practical emulsification. This type of measurements, combined with determinations of particle size, cataphoretic velocity, hydrogen-ion concentration, and viscosity, hace helped in the decelopment of methods of preparing stable and highly dispersed emulsions.the interface. In the instrument as supplied by the makers, t h e p l a t f o r m supporting the beaker is raised by a thumbscrew until the interfacial surface exerts an upward force on the ring. After each movement of the thumbscrew which raises the platform, the torsion head which measures the force is adjusted.More definite and reproducible results can be obtained if the platform is raised a t a constant slow rate by a suitable motor-driven mechanism instead ent interfacial film; is described and new data are shown in the form of curves. The method depends upon the use of a modified du Kouy interfacial tensiometer which is an instrument designed for the measurement of the surface tension a t the interface of two liquid phases. This instrument as first described by its inventor in 1919(4) was suitable for use only with a liquid-gas interface. An improved model which can also be used for measurements on a liquid-liquid interface was reported in 1925 (5). Its construction and manipulation are more fully described by the manufacturer (3).The instrument consists essentially of a platinum ring of known diameter mounted horizontally and held in a sensitive mechanism which measures any vertical force exerted on the ring in dynes per centimeter of ring circumference. The films whose strength waB to be measured were prepared in multiple by adding a fresh, aqueous solution of the emulsify-of intermittently a n d i r r e g ularly by the thumbscrew. For this purpose a telechron motor (Warren Telechron Company, type CM, Model M-43) was used whose shaft has a constant velocity of four revolutions per minute, and which raises or lowers the platform a t a rate of 3.8 mm. per minute by means of the mechanism shown in Figure 1. The hands and attention of the operator are thus left free to control the torsion head which measures the force exerted by the rising film on the platinum ring.The platinum ring is delicate and easily...

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