To measure dilational viscoelasticity of the interfaces, sinusoidal
oscillations of the drops’ areas (Myrvold & Hansen, 1998) were
increased by volume amplitude of 0.5 mL (about 10% area amplitude)
at a frequency of 0.04 or 0.1 Hz. The resulting changes in
interfacial tension and interfacial area were collected and used to
calculate the dilational elastic modulus (E0) and phase angle
tangent (tan q) utilizing the DROPimage software. Drops were
suspended for 1–10 min before measurements. The E0 values
measured at 0.04 and 0.1 Hz are shown in Fig. 1. Increasing
frequency from 0.04 Hz to 0.1 Hz systematically shifts the interfacial
dilational modulus values to a higher level. All the following
measurements were conducted at a frequency of 0.1 Hz. Values
reported are the averages of a minimum of three replications. The E0
measured at 5 min were used for the calculations.