Spreading behaviour of aqueous trisiloxane solutions over hydrophobic polymer substrates

The kinetics of spreading of aqueous trisiloxane solutions over different solid hydrophobic substrates has been investigated experimentally. Two pure trisiloxane surfactants with 6 and 8 oxyethylene groups at concentrations close to the critical aggregation concentration and the critical wetting concentration were used in the spreading experiments. Three hydrophobic substrates (Teflon AF, Parafilm, and polystyrene) having different surface properties were used. It was found that the spreading behaviour depends on the hydrophobic/roughness properties of substrates. The rapid spreading and complete wetting were observed for both trisiloxane surfactant solutions at the critical wetting concentration on a substrate with a moderate hydrophobicity. For both highly hydrophobic Teflon AF and Parafilm substrates only partial wetting was found. The experiments have shown that the spreading behaviour over all substrates proceeds at two stages. At the critical aggregation concentration for both trisiloxanes on all substrates the time lag of the spreading was detected.