Interaction Forces in Thin Liquid Films Stabilized by Hydrophobically Modified Inulin Polymeric Surfactant. 1. Foam Films

Using the interferometric method of Scheludko−Exerowa for investigation of foam films, we have obtained results using a hydrophobically modified inulin polymeric surfactant (INUTEC SP1). Measurements were carried out at constant INUTEC SP1 concentration of 2 × 10-5 mol·dm-3 and at various NaCl concentrations (in the range 1 × 10-4 to 2 mol·dm-3). At constant capillary pressure of 50 Pa, the film thickness decreased gradually with an increase in NaCl concentration up to 10-2 mol·dm-3 NaCl above which the film thickness remains virtually constant at about 16 nm. This reduction in film thickness with an increase in NaCl concentration is due to the compression of the double layer and at the critical electrolyte concentration (Cel,cr = 10-2 mol·dm-3) the electrostatic component of the disjoining pressure is completely screened and the remaining pressure is due to the steric interaction between the adsorbed polymer layers. Disjoining pressure−thickness (Π−h) isotherms were obtained at Cel < Cel,cr (10-4 − 10-3 ...