Asymmetrical Two-Headed Linear Cationic Surfactants with Halogenoferrate Magnetic and Bromide Counterions: Synthesis,...

A series of multicharged surfactants with magnetic counterions (Mag-D-Surfs) containing one hydrophobic tail and two hydrophilic groupings, and comprising exclusively carbon atoms in the hydrophobic part, i.e., 2-alkyl-N,N,N,N',N',N'-hexamethylpropan-1,3-ammonium salts (ferrates; alkyl: decyl, dodecyl, and tetradecyl, abbreviated, respectively, as C₁₀-D_CMe₃Mag, C₁₂-D_CNMe₃Mag, and C₁₄-D_CNMe₃Mag), were first synthesized and characterized by FT-IR, Raman, X-ray fluorescence (XRF), and FIR spectra as well as elemental analyses. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), supported by optical polarization microscopy, showed that the coexistence of isotropic and anisotropic subphases depended on cooling rates. Surface activity of C_n-D_CNMe₃Mag at the air/water interface was evaluated by measuring the surface tension of their solutions by the pendant drop technique and compared with surfactants without magnetic function. Moreover, surface tensiometry in a magnetic field demonstrated that the studied Mag-D-Surfs exhibited magnetically induced changes in the drop shape. Their magnetic behavior in the solid state was determined by superconducting quantum interference device magnetometry (SQUID). All findings related to the aforementioned double-headed Mag-D-Surfs were compared to linear magnetic ionic liquids surfactants (MILSs), i.e., alkyltrimethylammonium halogenoferrates (alkyl: dodecyl [DTA][FeCl_xBr_4-x^-], tetradecyl [TTA][FeCl_xBr_4-x^-], and cetyl [CTA][FeCl_xBr_4-x^-]). Magnetic tests confirm the paramagnetic nature of the studied compounds and the 1:1 molar ratio (surface active cation:Fe³⁺) for all the studied surfactants. Their unique physicochemical properties demonstrate exceptional performance, particularly in the development of new stimuli-responsive materials.