Wetting films from aqueous solutions of polymeric surfactants on hydrophobic solid surface

Wetting films from aqueous solutions of three different polymeric surfactants (hydrophobically modified inulin with two degrees of substitution, INUTEC SP1 and HMI-B, and hydrophobically modified polyacrylate, EFKA) were obtained on hydrophobic glass surfaces with different degrees of hydrophobicity. The equilibrium film thickness h was measured as a function of polymeric surfactant concentration C. For surfaces with low degree of hydrophobicity h increased, whereas for surfaces with high hydropobicity h decreased, with increase of CSP1. For HMI-B with higher degree of substitution h remained virtually constant for surfaces with low degree of hydrophobicity, while for high degree of hydrophobicity h increased with increase of CHMI-B. With EFKA h decreased with increase of polymeric surfactant concentration. The addition of 0.05 M NaCl caused a significant reduction in film thickness. A tentative explanation of the differences between the three polymeric surfactants was given in terms of the electrostatic interaction contribution. Two main features have been established: (i) stable films exist at high polymeric surfactant concentration and low degree of hydrophobicity of the solid surface; (ii) unstable films that rupture at low polymeric surfactant concentration and high degree of hydrophobicity of the solid surface.