Polyoxyalkylated diethylenetriamine polymeric surfactants: molecular structure effect on thin wetting films

Abstract

Thin wetting films from aqueous solution of four polyoxyalkylated diethylenetriamine (DETA) polymeric surfactants (named A, B, C, and D) are studied. Surfactants A, B, and C have a star-like structure differing only by the number of polymeric branches: four, six, and nine in the mentioned order while the forth one, D, is of a dendritic type with four to six primary and two to three secondary branches. The receding contact angles θr of the solution on hydrophilic SiO2 glass surface and the contact angle θaq of a drop of doubly distilled water on SiO2 glass surface pretreated with DETA polymeric surfactant solution are measured. The θr values on hydrophobicity of SiO2 glass surface, respectively, increase in the following order: surfactant A, surfactant C, surfactant B, and surfactant D. The equilibrium thickness heq of wetting films from DETA aqueous solution on hydrophilic SiO2 glass surface is measured using the micro-interferometric method. Results show an unexpected course of the heq vs. Cs curves with a maximum. Results from the studies indicate that differences in polymeric surfactant molecular structure affect the properties exhibited at air/liquid and solid/liquid interfaces, such as the value of surface tension, degree of hydrophobicity of solid surface, equilibrium film thickness, etc.