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The influence of surfactant structure on foam properties of different alkyl polyglycosides (APGs) in aqueous solutions was studied. Foamability, foam stability, and foam morphology were analyzed using the FoamScan method. Results showed that the foamability, foam stability, and the liquid carrying ability of long-chain APGs are higher than those of short-chain APGs. Foam morphology analysis showed that the foam produced by short-chain APGs is more unstable than the foam generated by longchain APGs. Long-chain APGs have stronger intermolecular cohesion force, stringency, and ductility than shortchain APGs.

The 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.

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