Effects of the Polypropylene Oxide Number on the Surface Properties of a Type of Extended Surfactant

Abstract

AbstractThe surface properties of 5 extended surfactant C12–14P mE2S solutions in pure water and 0.1 M NaCl were investigated through surface tension and electrical conductivity measurements. The surface properties measured include the critical micelle concentration (CMC), critical surface tension (γcmc), maximum surface excess concentration (Γmax), minimum area occupied per surfactant molecule (Amin), and efficiency in surface tension reduction (pC20). The CMC values of the 5 surfactants decreased with increasing polypropylene oxide number (PON) and were higher than those obtained in 0.1 M NaCl. The Γmax values showed a downward trend whereas the Amin values exhibited an upward trend with increasing PON without NaCl. The Γmax values were higher and the Amin values were lower than those obtained without 0.1 M NaCl. The CMC values increased at elevated temperatures. The CMC values of C12–14P3E2S, C12–14P5E2S, and C12–14P8E2S were similar but were markedly lower than those of C12–14E2S at different temperatures. When PON was less than 12, the log CMC value decreased linearly with increasing PON in the absence of salt, and the relationship between pC20 and PON was linear. But in the presence of 0.1 M NaCl, the log CMC value decreased exponentially with increasing PON.