Cleavable Gemini Cationic Surfactants: Experimental and Theoretical Description of Adsorption

Abstract

The aim of the present study was to examine, both experimentally and theoretically, the interfacial behavior of cleavable gemini ester quat-type cationic surfactants in comparison to a standard gemini representative. For the theoretical description of the air/water surface tension isotherms of the corresponding geminis, a modified model of multiply charged ionic surfactant adsorption (surface quasi-two-dimensional electrolyte, STDE), taking into account counter ion specificity and formation of surfactant ioncounter-ion associates, was used. As a result, good agreement between theory and experiment was obtained.Following the example of Nature, the researchers have designed a variety of novel ecologically safe amphiphiles, which are functionalized with structural motifs, borrowed from biological systems, and thus often possess new interesting physicochemical and biological functionalities. 13 The search for environmentally friendly surfactants and a basic understanding of their self-assembling phenomena are of immense current interest because of the emerging necessity for specific applications in several areas, such as new cosmetic formulations and drug delivery systems, and in nanotechnology. Furthermore, the grafting of a labile moiety onto the hydrophobic backbone of the surfactant structure makes it possible to obtain high-quality environmentally friendly products with multifunctional capabilities, improved performances, and lower toxicities. The introduction of weak (so-called "labile") bonds into the hydrophobic backbone of the surfactant structure makes it possible to improve the rate of biodegradation and to obtain the most suitable environmentally friendly products. Labile groups such as ester, amide, and acetal groups deliberately inserted into surfactant structure are commonly called cleavable. In the literature, the terms chemodegradable, destructible, triggerable, temporary, hydrolyzable, and acid-(alkali-)sensitive surfactants can also be found. 47 The most well-known, and probably the most commercially viable, example of cleavable surfactants comprises the family of ester quats, i.e., cationic surfactants with an ester bond inserted between the hydrocarbon tail(s) and the quaternary ammonium head group(s).In the present work, we attempted to describe quantitatively and qualitatively the nonequivalent adsorption (considered both experimentally and theoretically) of cleavable newly synthesized cationic gemini ethylenebis[N,N-dimethyl-N-(n-alkyl)oxycarbonyl(methyl)methylammonium] dibromides (TMEAL-nBr; n = 10, 12) in relation to standard N,N,N¤,N¤-tetramethyl-N,N¤-di(dodecyl)ethylenediammonium bromide [d(DDA)EBr] in terms of the surface quasi-two-dimensional-electrolyte (STDE) model modified for multicharged structures. 810The studied ester quat-type gemini compounds were synthesized according to the method shown in Scheme 1. The obtained surfactants were purified by repeated crystallization until no impurities could be detected by 1 H NMR spectroscopy.The chemical structures of the compounds were det...

Adsorption Properties of Surface Chemically Pure Sodium Perfluoro-n-alkanoates at the Air/Water Interface: Counterion Effects within Homologous Series of 1:1 Ionic Surfactants

“…It is the Debye length that also plays the crucial role in it. ,, Thus, this approach may harmonize the adsorption properties of nonionic and anionic amphiphiles. However, the few experimental studies applied so far to test this theoretical approach of the so-called quasi-two-dimensional-electrolyte (STDE) cannot help us to determine its efficiency in general because of some inadequacies. − Thus, for example, the surfactant solutions used to test it cannot stand the strict requirement of surface-chemical purity. In addition, cleavable surfactants with complicated chemical structures have been applied, which are degraded and may hydrolyze in solution − As a result, the quality of the experimental σ e versus log c isotherms is insufficient, which is why there are a few absurdities in the quantitative molecular interpretation of the adsorption parameters.…”

Multiheaded Cationic Surfactants with Dedicated Functionalities: Design, Synthetic Strategies, Self-Assembly and Performance

“…[1]. In particular, the previously developed Surface Quasi-Two-Dimensional Electrolyte (STDE) model of surfactants adsorption at the water/air interface [71] and later expended [1,11,72] is convenient for describing the adsorption properties of a variety of multiheaded cationic surfactants. Recalling, the STDE model assumes that, due to the strong electric field, the counterions can penetrate the Stern layer, treated as a surface quasi-two-dimensional electrolyte (STDE), in which the electroneutrality condition is not met.…”