Aggregation Behavior of “Linear” Trisiloxane Surfactant with Different Terminal Groups (CH₃–, ClCH₂–, and CF₃−) in Aqueous Solution

Abstract

Novel "linear" trisiloxane surfactants with different terminal groups (CH 3 −, ClCH 2 −, CF 3 −) and two polyether hydrophilic groups were successfully synthesized and confirmed using 1 H NMR, 13 C NMR, 29 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 3 −EO 8 , Cl−Si 3 − EO 8 , and F−Si 3 −EO 8 ) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC (γ CMC ) and single trisiloxane surfactant molecule at the air/water interface (A min ) values. Following the difference in the intermolecular forces and molecular volumes (CH 3 − < ClCH 2 − < CF 3 −), the γ CMC values decrease following the order Me− Si 3 −EO 8 > Cl−Si 3 −EO 8 > F−Si 3 −EO 8 , and the adsorption efficiency (pC 20 ), surface pressure at the CMC (π CMC ), CMC/C 20 , and A min values increase following the order Me−Si 3 −EO 8 < Cl−Si 3 −EO 8 < F−Si 3 −EO 8 . As comparison, fluorinated trisiloxane surfactant (F−Si 3 −EO 8 ) has greater surface activity attributed to the terminal CF 3 − group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.

Role of isomers and steric hindrance in the micellization of carboxylated carbosilane surfactants

“…To date, the influence of molecular architecture on the fundamental interfacial properties of siloxane surfactants have been well investigated (Aramaki et al, 2019; Chen & Tan, 2020; Pukale et al, 2019; Schmaucks et al, 1992; Tan et al, 2013; Tan, Xiong, He, et al, 2019; Tan, Xiong, & Hu, 2019; Tan & Zhang, 2022b; Wang et al, 2014, 2017; Zeng et al, 2016), for example, trisiloxane and tetrasiloxane surfactants (Huang, Zhang, et al, 2020; Schmaucks et al, 1992), siloxane surfactants with multiple headgroups (Zeng et al, 2016), Gemini surfactants (Chen et al, 2018), polysiloxane surfactants (Wang et al, 2017), and so forth. Du et al investigated (poly)siloxane surfactants with various molecular architecture ranging from single‐tail/single‐headgroup type to double headgroups based to Gemini, and demonstrated that butynediol‐ethoxylate based siloxane surfactants exhibited excellent surface properties and can self‐assemble into 50–1000 nm spherical aggregates (Pukale et al, 2019; Wang et al, 2014; Wang et al, 2017).…”

Role of isomers and steric hindrance in the micellization of carboxylated carbosilane surfactants

“…Tan et al reported the in uences of molecular structure, headgroup structure (polyether, imidazolium, pyridinium, pyrrolidium, etc. ), unsaturation within the trisiloxane group, alkyl groups and steric hindrance, linear versus "T"/umbrella shape trisiloxane, on the surface properties and micellization [3,[11][12][13][14][15]. It was concluded that structural variations, the structure of hydrophobic (poly)siloxane or hydrophilic headgroups, play a vital and constructive role in their aggregation behavior [16][17][18].…”

“…To date, the in uence of molecular architecture on the fundamental interfacial properties of siloxane surfactants have been well investigated [5][6][7][8][9][10][11][12][13][14][15], for example, trisiloxane and tetrasiloxane surfactants [3,5], siloxane surfactants with multiple headgroups [7], Gemini surfactants [2], polysiloxane surfactants [8], and so forth. Du et al investigated (poly)siloxane surfactants with various molecular architecture ranging from single-tail/single-headgroup type to double headgroups based to Gemini, and demonstrated that butynediol-ethoxylate based siloxane surfactants exhibited excellent surface properties and can selfassemble into 50 to 1000 nm spherical aggregates [8-10].…”

Virtual Issue on Surfactants

“…Finally, it was concluded that some micelle demixing is occurring between the gemini and the zwittergent under certain micellar composition ranges, a phenomenon rarely associated with hydrocarbon surfactants. Again, Tan et al synthesized novel “linear” trisiloxane surfactants with different terminal groups (CH 3 –, ClCH 2 –, CF 3 −) and two polyether hydrophilic groups followed by successful characterization using the 1 H NMR, 13 C NMR, 29 Si NMR, and FTIR spectroscopy . In addition to this, the aggregation and adsorption behaviors of these surfactants in aqueous solution were studied by surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM).…”

“…Again, Tan et al synthesized novel "linear" trisiloxane surfactants with different terminal groups (CH 3 −, ClCH 2 −, CF 3 −) and two polyether hydrophilic groups followed by successful characterization using the 1 H NMR, 13 C NMR, 29 Si NMR, and FTIR spectroscopy. 8 In addition to this, the aggregation and adsorption behaviors of these surfactants in aqueous solution were studied by surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM). On the other hand, it was concluded that the fluorinated trisiloxane surfactant (F−Si 3 −EO 8 ) has greater surface activity attributed to the terminal CF 3 − group.…”