A Surface Rheological Study of Silwet L-77 Surfactant at the Air/Water Interface

Abstract

The dilational viscoelastic properties of Silwet L-77, a trisiloxane surfactant of the general formula (Me₃SiO)₂SiMe(CH₂)₃(OCH₂CH₂)_7.5OH, at the air/water interface were investigated. Aqueous solutions of Silwet L-77 were spread onto a pendant drop and the dynamic surface tensions were measured by means of axisymmetric drop shape analysis. The surface dilatational elasticity, viscosity, and phase angle of the adsorption monolayer were also determined using the oscillating drop technique. The influences of frequency and concentration on the surface dilational properties were expounded. It is shown that the surface dilational modulus and elastic modulus increased with the increase of frequency, the viscous modulus was complex, while the phase angle decreased with the increase of frequency. Surface dilational modulus, elastic modulus, and viscous modulus passed through the maximum with the increase of bulk concentration and the phase angle increased with the increase of concentration.

Keywords:

• Dilational viscoelasticity
• elastic modulus
• phase angle
• trisiloxane surfactant
• viscous modulus

Acknowledgments

The authors are thankful for the financial support of the Natural Science Foundation of China (No. 20976003) and the Research Program of Beijing Municipal Commission of Education (No. KM201010011003).