Determination of surface area and particle size of synthetic latex by adsorption I. Latices containing fatty acid soaps

Abstract

A method is described for the determination of the surface area and average particle size of synthetic latices containing fatty acid soaps. The method involves the titration of a latex with soap until the critical micelle concentration of the soap in solution is attained. From the total amount of soap adsorbed per gram of polymer at this point, and the effective molecular surface area of the soap, the above quantities can be calculated. The particle size given by this method is a volume to surface average diameter. Two techniques have been used to determine the titration end point, surface tension and conductance. Both methods give identical results. A scheme is also presented by which correction can be applied for the amount of unadsorbed soap in solution without assumption of the value of the critical micelle concentration of the soap used. In the soap titrations any free fatty acid present in the latices is completely displaced from the polymer surface by the added soap. The effective molecular soap areas required in the calculation of particle size and area have been determined for laurate, myristate, oleate, palmitate, stearate, and OSR soaps. It is shown that these areas are valid from about room temperature to 50°C.