Aggregation properties of siloxane surfactants with phenyldimethylsiloxyl groups in aqueous solution

Abstract

Two siloxane surfactants (Ph-Si3-EO16 and Ph-Si4-EO16) with two or three phenyldimethylsiloxyl groups were successfully synthesized by Piers-Rubinsztajn and thiol-ene reaction. The aggregation behavior in aqueous solution was investigated by surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and freeze-fracture transmission electron microscopy (FF-TEM). Owing to the steric hindrance and hydrophobicity of phenyldimethylsiloxyl groups, Ph-Si3-EO16 (40.4 mN·m−1) and Ph-Si4-EO16 (35.4 mN·m−1) have higher γCMC values. In comparison with Ph-Si3-EO16, Ph-Si4-EO16 has smaller CMC, γCMC, and Amin values attributed to the three phenyldimethylsiloxyl groups and intermolecular interaction. In the aqueous solution of Ph-Si4-EO16, the coexistence of spherical and rodlike aggregates resulting from intermolecular interaction (π-π interactions) was confirmed by TEM and FF-TEM. The results show that phenyldimethylsiloxyl groups play a vital role in the aggregation behavior of siloxane surfactants.