Effect of Oxyethylene Numbers on Surface Dilational Properties of Alkyl Secondary Alcohol Ethoxylates

Abstract

The surface dilational viscoelasticity properties of alkyl secondary alcohol ethoxylates solutions, C₁₅-s-EO₇, C₁₅-s-EO₁₂, and C₁₅-s-EO₂₀, were investigated using the oscillating barrier method and interfacial tension relaxation method in Langmuir trough. The influences of oxyethylene numbers on dilational properties were expounded. The results show that the dilational modulus decreases with an increase in polyoxyethylene numbers at low concentration, which may be attributed to the fact that the surface concentration of C₁₅-s-EO_n with lower EO numbers is greater than that of C₁₅-s-EO_n with higher EO numbers. However, an increase in polyoxyethylene numbers cause an increase in dilational modulus at high concentration, which may be attributed to the slower relaxation processes caused by the “flat configuration” of the longer polyoxyethylene chain at the surface. The results from the interfacial tension relaxation method are in good agreement with the experimental results from oscillating barrier method.

Keywords:

• Alkyl secondary alcohol ethoxylates
• dilational modulus
• interfacial tension relaxation
• phase angle
• surface

Acknowledgements

The authors are grateful for the financial support from the National Science & Technology Major Project (2008ZX05011), the National High Technology Research and Development Program (2008AA092801), and the Knowledge Innovation Program of the Chinese Academy of Sciences (KJCX1-YW-21-03).

Notes

Notes. cmc = critical micelle concentration; HLB = hydrophilic-lipophilic balance number.