Hydrophilicity and flexibility of the spacer as critical parameters on the aggregation behavior of long alkyl chain cationic gemini surfactants in aqueous solution

Abstract

Series of quaternary ammonium-based gemini surfactants with long alkyl chains (C12 and C18) containing different spacers and substituents attached to the polar head group have been synthesized and their aggregation properties in aqueous solution examined. The effect of the hydrophobic chain, the nature and structure of the spacer group and the polarity of the head group on the aggregation behavior of such dimeric surfactants has been investigated. The critical micelle concentration (cmc) values of gemini surfactants in aqueous solution were determined by conductivity, steady state fluorescence and potentiometric measurements. The size of aggregates formed by investigated amphiphiles above the cmc in aqueous solution was examined by dynamic light scattering. Gemini surfactants show cmc values significantly lower than those of comparable single chain surfactants. The tendency of trimeric surfactants with a rigid spacer to form aggregates is higher than that of the corresponding dimeric surfactants. As occurs for monomeric ionic surfactants, the cmc of gemini surfactants decreases with the elongation of the hydrophobic chain. However, the effect of lengthening the alkyl chain on the cmc depends on the structure of the spacer. C12 gemini surfactants with a rigid hydrophobic spacer exhibit cmc higher than those containing a flexible hydrophobic spacer. For gemini surfactants with C18 alkyl chains this effect is even more pronounced and leads to differences in cmc values greater than one order of magnitude. The structure of the spacer, flexible or rigid chain, has been found to be a critical parameter on the self-assembly of long chain gemini surfactants. Spherical micelles are spontaneously formed above the cmc for C12 gemini surfactants, whereas trimeric and C18 gemini surfactants seems to form vesicle-like aggregates when self-aggregation occurs.

Modified Chitosan as a “Multi‐subtype” Macromolecular Emulsifier for Preparing Asphalt Emulsion

“…The γ ‐lg c curve of MCTS was shown in Figure , and the relevant surface activity parameters are given in Table . As shown in Table , we found that the CMC of the surfactant solution is merely 0.064 g L‐1, and the corresponding surface tension of the solution is 38.85 mN m‐1 at 298 K, which is lower than that of the Gemini surfactants . In brief, it may be explained by that the MCTS formed the cross‐linked network by the intermolecular and intramolecular hydrogen bonds (Figure ), which made molecules closer and facilitate the adsorption of surfactants at the surface of the solution and decrease the CMC.…”

Synthesis, Surface Activity, Thermodynamic Parameters, and Performance Evaluation of Branched Carboxylate Gemini Surfactants

“…As illustrated in Fig. , the minimum value of I 1 /I 3 is decreased with the increment of the hydrophobic alkyl chain length, implying that the longer alkyl tail leads to the palisade layer more compact and has a reduction for polarity (Garcia et al, ; Martin et al, ). It can be clearly noticed from Table that the obtained values of CMC are 1.93, 0.352, and 0.311 mmol L −1 for 3C 8 taDA, 3C 10 taDA, and 3C 12 taDA, respectively, which are in accordance with those obtained from surface tension measurements at 298.15 K.…”

Aggregation and pH Responsive Behavior of Thioester Surfactants and Formation of Disulfide Linkages in Aqueous Solutions

“…The results of the conductivity and SPQ fluorescence probe methods are summarized in Table 1. DLS measurements have been conducted to estimate the hydrodynamic diameter of the aggregates 20,21 .…”