ADSORPTION OF SMALL SILICONE POLYETHER SURFACTANTS AT THE AIR WATER INTERFACE/

Silicone polyether copolymers are used in a diverse number of applicat ions, for instance, as foam stabilizers, wetting agents, and emulsifie rs. We have explored the effect of surfactant structure, specifically the ethylene oxide (EO) chain length of a series of(Me(3)SiO)(2)Si(Me) -(CH2)(3)(EO)(x)OH (or Bis-(EO)(x)OH) molecules, on (1) the surfactant adsorption at the air/water surface, (2) the minimum surface tension of the surfactant solution, and (3) the critical aggregation concentra tion(CAC). The surface adsorption of these species does not vary with EO lengths x = 4-16, but decreases when x > 16. The results for x = 4- 16 are consistent with a tightly packed surface monolayer whose area/m olecule is determined by the dimensions and conformation of the Bis gr oup, and the close packing of the Bis methyl groups is responsible for the low surface tension. For x > 16, the EO chain penetrates the surf ace and disrupts the close packing. Other findings include that the mi nimum surface tension increases as x increases. The CAC also increases as x increases, reflecting the increase in hydrophilicity of the surf actant as the EO content of the copolymer increases.