Dilational Rheological Properties of P-(n-alkyl)-benzyl Polyoxyethylene Ether Carboxybetaine at Water–Decane Interface

Abstract

The dilational rheological behaviors of absorbed films of p-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine C_xBE₂CB (x = 8, 10, 12) at the water–decane interface have been investigated by the drop-shape analysis method. The influences of time, oscillation frequency, and bulk concentration on dilational modulus and phase angle have been expounded. The experimental results show that the phase angle of C_xBE₂CB (x = 10, 12) decreases with the increase of time, the slope of the log ϵ − log ω curve and phase angle of C_xBE₂CB (x = 10, 12) decrease in a wide concentration range. These phenomena become more and more apparent with the increase of hydrocarbon chain length and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. Therefore, the compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sublayer play a more important role for C_xBE₂CB (x = 10, 12) adsorption film. The dependence of dilational modulus on interfacial pressure can support our provided mechanism strongly.

Keywords:

• Dilational modulus
• dilational phase angle
• dilational rheology
• interface
• interfacial pressure
• P-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine