Aggregation Behavior of "Linear" Trisiloxane Surfactant with Different Terminal Groups (CH3-, ClCH2-, and CF3-) in Aqueous Solution.

Novel "linear" trisiloxane surfactants with different terminal groups (CH3-, ClCH2-, CF3-) and two polyether hydrophilic groups were successfully synthesized and confirmed using 1H NMR, 13C NMR, 29Si NMR, and FT-IR spectroscopy. The aggregation and adsorption behavior of the "linear" trisiloxane surfactants in aqueous solution was studied by surface tension, dynamic light scattering (DLS), transmission electron microscopy (FF-TEM), and TEM. Owing to the introduction of two polyether hydrophilic groups in the terminal positions of the trisiloxane hydrophobic part, "linear" trisiloxane surfactants (Me-Si3-EO8, Cl-Si3-EO8, and F-Si3-EO8) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC ( γCMC) and single trisiloxane surfactant molecule at the air/water interface ( A min) values. Following the difference in the intermolecular forces and molecular volumes (CH3- < ClCH2- < CF3-), the γCMC values decrease following the order Me-Si3-EO8 > Cl-Si3-EO8 > F-Si3-EO8, and the adsorption efficiency ( p C20), surface pressure at the CMC ( πCMC), CMC/ C20 , and A min values increase following the order Me-Si3-EO8 < Cl-Si3-EO8 < F-Si3-EO8. As comparison, fluorinated trisiloxane surfactant (F-Si3-EO8) has greater surface activity attributed to the terminal CF3- group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.