Some Adsorption Characteristics of Sodium decyl and dodecyl Sulphates on the surface of Emulsifier-free Polymer Latex Particles
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The adsorption characteristics of sodium decyl and dodecyl sulphates on polystyrene latex particles have been investigated. The study involves the addition of known amounts of the surfactant to an emulsifier-free latex, allowed to equilibrate at 33°C, and separating the two phases by a high speed centrifugation. The remaining concentration of the emulsifier is complexed with a solution of methylene blue and extracted by an organic solvent . the absorption of the organic phase is then measured at 610 nm. The adsorption isotherm is determined from the concentration profile from which the amount of emulsifier adsorbed is calculated. Knowing the average particle size, and consequently, number concentration of latex particles, allows the calculation of the moleculer area, Ag of the emulsifier in the saturated monolayer at the interface. This was found to be as 62A°2 for the decyl sulphate and 37A °2 for dodecyl sulphate in the presence of 0.1 M NaCl. The limiting molecular area, Ao were, respectively, 59 and 28 A° . The presence of electrolyte displaces the isotherms to lower equilibrium concentrations and, greatly, reduces the extent of hydrolysis of the surfactants.