3.2. Interfacial dilational rheology
The complex viscoelastic modulus of the water–soybean oil with PGPR showed a slight decrease along time, keeping a value of approximately 5 mN/m (Fig. 5). This value was the highest among the evaluated systems. At water–hexadecane interface with PGPR, the complex modulus increased with time from about 1.5 mN/m to 4 mN/m. On the other hand, Span 80 at water–soybean oil interface led to a steep decrease in complex viscoelastic modulus with time, reaching values near zero. At water–hexadecane interface, a low viscoelastic modulus (about 2 mN/m) was kept constant along time. The modulus at the water–soybean oil interface with lecithin decreased from a high value (about 35 mN/m) to decrease up to values near 2 mN/m. The results of the water–hexadecane interface with lecithin oscillated between 20 and 100 mN/m, although those results are not so reliable, since the surface area of the drop extensively changed with time (data not shown).