Dynamic surface properties and dilational rheology of acidic and lactonic sophorolipids at the air-water interface.

•Dynamic surface tension curves of acidic and lactonic SLs were investigated.•The dilational properties of the surface adsorptive film were investigated.•Lactonic SLs have a high diffusive rate from the bulk phase to the subsurface.•Adding NaCl increases the D values of acidic and lactonic SLs.•Lactonic SLs exhibit a relatively small dilational elasticity.