Adsorption behavior of branched polyoxyethylene ether carboxylate surfactants

In our work, branched anionic surfactant (3, 5, 7-trimethyl decanol polyoxyethylene ether carboxylate (A(13)EC(5-)Na)) has been successfully synthesized and characterized by fourier transform infrared (FT-IR) spectra. Static equilibrium surface tension, contact angle and dynamic surface tension of alcohol ether carboxylic acid (A(13)EC(5-)H), alcohol ether carboxylate (A(13)EC(5)-Na) and linear chain carboxylate (A(12)EC(5)-Na, as comparison) were investigated to study their spreading and adsorption behaviors. Electrolyte tolerance of anionic surfactants (A(13)EC(5)-Na and A(12)EC(5)-Na) was also studied to explore the application in enhanced oil recovery. The results indicated that critical micelle concentration (CMC) and minimum area per molecule (A(0)) are the lowest and the surface excess concentration (Gm) is the highest for nonionic surfactants (A(13)EC(5)-H). A(13)EC(5)-Na can decrease the surface tension of water to 27.43 mN/m. Due to the introduction of branched chains, Gm of A(13)EC(5)-Na is smaller than that of A(12)EC(5)-Na. And the adsorption efficiency and the efficiency of forming micelles of A(13)EC(5)-Na molecules are superior to that of A(12)EC(5)-Na. By contact angle and dynamic surface tension measurements, we can know that for branched products, the wetting ability is stronger, diffusion rate to the interface is faster and the time of surface tension reaching equilibrium is shorter. The adsorption process of A(13)EC(5)-Na is diffusion controlled, while the adsorption process of A(12)EC(5)-Na is mixed diffusion-kinetic adsorption mechanism. CaCl2 tolerance of A(13)EC(5)-Na is stronger than that of A(12)EC(5)-Na but NaCl tolerance of A(12)EC(5)-Na is stronger.