Aggregation Behavior of "Linear" Trisiloxane Surfactant with Different Terminal Groups (CH-, ClCH-, and CF-) in Aqueous Solution.

Novel "linear" trisiloxane surfactants with different terminal groups (CH-, ClCH-, CF-) and two polyether hydrophilic groups were successfully synthesized and confirmed using H NMR, C NMR, Si 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-Si-EO, Cl-Si-EO, and F-Si-EO) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC ( γ) and single trisiloxane surfactant molecule at the air/water interface ( A ) values. Following the difference in the intermolecular forces and molecular volumes (CH- < ClCH- < CF-), the γ values decrease following the order Me-Si-EO > Cl-Si-EO > F-Si-EO, and the adsorption efficiency ( p C), surface pressure at the CMC ( π), CMC/ C , and A values increase following the order Me-Si-EO < Cl-Si-EO < F-Si-EO. As comparison, fluorinated trisiloxane surfactant (F-Si-EO) has greater surface activity attributed to the terminal CF- group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.