Dynamic Surface Tension of Heterogemini Surfactants with Quaternary Ammonium Salt and Gluconamide or Sulfobetaine Headgroups.

Dynamic surface tensions of two types of heterogemini surfactants with nonidentical hydrophilic headgroups consisting of a quaternary ammonium salt (cationic) and a gluconamide (nonionic) or sulfobetaine (zwitterionic) group were measured using the maximum bubble pressure method. For these compounds, effects of alkyl chain length, structure of the hydrophilic groups, and surfactant concentration were investigated using diffusion coefficients and parameter x. The parameter x is related to the difference between the energies of adsorption and desorption of the surfactant. The values of x of heterogemini surfactants increased as the alkyl chain length increased, and they were slightly larger than that for the corresponding monomeric surfactant. This is because of an increase in hydrophobicity caused by two alkyl chains, as well as interactions between two different hydrophilic groups. Adsorption rate of the heterogemini surfactants decreased with increasing alkyl chain length, indicating slow dynamics, and inhibited adsorption to the air/water interface as the chain length increased. However, at higher concentrations, the heterogemini surfactants showed rapid and effective adsorption and increased adsorption rates at higher concentrations. Diffusion coefficients of the heterogemini surfactants decreased with increasing concentrations for all chain lengths, indicating diffusion of the solute molecules to the subsurface and adsorption of the solute from the subsurface to the surface.

Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups 2: aggregation behavior studied by SANS, DLS, and cryo-TEM.

The aggregation behavior in aqueous solution of zwitterionic heterogemini surfactants, N,N-dimethyl-N-[2-(N'-alkyl-N'-ß-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C(n)AmCa, in which n represents hydrocarbon chain lengths of 8, 10, 12, and 14), with nonidentical headgroups containing ammonium and carboxylate was investigated through small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. We found that the aggregation behavior of 2C(n)AmCa strongly depended on the hydrocarbon chain length and the surfactant concentration. 2C(8)AmCa forms spherical micelles with radius of approximately 2 nm in solution. 2C(10)AmCa forms rod-like micelles at low concentration in the solution, and the structure changes to vesicles with increasing concentration. The membrane thickness of the vesicle is independent of the surfactant concentration. Aggregation shape transitions were also observed for 2C(12)AmCa. In addition, it appears that the vesicles of 2C(12)AmCa coexist with the rod-like micelles at a wide range of surfactant concentrations. Interestingly, 2C(14)AmCa forms vesicles with averaged membrane thickness of 2.32 nm in solution, even at the extremely low concentration of 10 times the cmc. Thus, it was concluded that 2C(n)AmCa exhibits unique aggregation behavior, such as the formation of spherical micelle→rod-like micelle→rod-like micelle+vesicle (coexistence)→vesicle with increasing hydrocarbon chain length and surfactant concentration. We also found that the membrane structure is an interdigitated bilayer when the vesicles are formed. This formation of interdigitated structures is related to the origins of the effective properties of 2C(n)AmCa in solution.

Adsorption and aggregation properties of heterogemini surfactants containing a quaternary ammonium salt and a sugar moiety.

A novel heterogemini surfactant comprising two hydrocarbon chains and two different hydrophilic groups such as a quaternary ammonium cation and gluconamide nonion N,N-dimethyl-N-[2-(N'-alkyl-N'-gluconamide)ethyl]-1-alkylammonium bromides (2CnAmGlu, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14) was synthesized by reacting N,N-dimethylethylenediamine with alkyl bromide, followed by a reaction with 1,5-D(+)-gluconolactone. The adsorption properties of 2CnAmGlu were characterized by surface tension measurements made using the Wilhelmy plate method, and their aggregation properties were investigated by dynamic light scattering and cryogenic transmission electron microscopy techniques. The relationship between the hydrocarbon chain length and the logarithm of the critical micelle concentration (cmc) for 2CnAmGlu exhibited a linear decrease when the chain length was increased up to 12 and then a departure from linearity at n=14. The surface tension reached 24-26 mN m-1 at each cmc, indicating high efficiency in lowering the surface tension of water. Furthermore, it was found that the structure of the aggregate formed for 2CnAmGlu in solution was influenced by the hydrocarbon chain length; that is, for n=10 and 12, micelles with a hydrodynamic radius of 2-5 nm were formed, whereas vesicles were also observed for n=14.

Surface tension and micellization properties of heterogemini surfactants containing quaternary ammonium salt and sulfobetaine moiety.

A novel gemini surfactant with two hydrocarbon chains and two different hydrophilic parts containing a quaternary ammonium salt and a sulfobetaine moiety, N,N-dimethyl-N-{2-[N'-methyl-N'-(3-sulfopropyl)-alkylammonium]ethyl}-1-alkylammonium bromides (2C(n)AmSb, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14), was synthesized by reacting N,N,N'-trimethylethylenediamine with n-alkyl bromide, followed by reacting with 1,3-propane sultone. The adsorption and aggregation properties of 2C(n)AmSb in the absence and presence of NaCl were characterized by the measurement of surface tension, steady-state fluorescence, and dynamic light scattering. The critical micelle concentration (cmc) and surface tension at the cmc of 2C(n)AmSb were compared with those for the corresponding monomeric surfactants, their mixtures, and gemini surfactants. The poor solubility in water shown by 2C(n)AmSb was improved by the addition of NaCl. The cmc of 2C(n)AmSb in the presence of NaCl is lower than that in the absence of NaCl, and the surface tension is almost identical for both systems. The radius of the aggregates formed by 2C(n)AmSb in a solution containing NaCl is found to be 0.70+/-0.3, 2.5+/-0.7, 5.6+/-1.4, and 10.7+/-2.4 nm for n=8, 10, 12, and 14, respectively. The particle size increases with an increase in hydrocarbon chain length; in particular, relatively large aggregates are formed for n=12 and 14.

Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups. 1. Adsorption and micellization.

Zwitterionic heterogemini surfactants with two hydrocarbon chains and two different hydrophilic groups, N,N-dimethyl-N-[2-(N'-alkyl-N'-beta-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C(n)AmCa, where n represents the hydrocarbon chain lengths of 8, 10, 12, and 14), were synthesized by N,N-dimethylethylenediamine with alkyl bromide, followed by reaction with succinic anhydride. One of the hydrophilic groups is a carboxylate anion, and the other is an ammonium cation. Their physicochemical properties were characterized by measuring equilibrium and dynamic surface tension, fluorescence intensity of pyrene, and light-scattering intensity. A relationship between a logarithm of critical micelle concentration (cmc) and hydrocarbon chain length showed a linear decrease upon increasing chain length and then a departure from linearity at n = 14. This is due to the existence of premicellar aggregations at concentrations below the cmc for n = 14. The surface tension of 2C(n)AmCa reached 27-30 mN m(-1) at each cmc, indicating efficiencies typical of hydrocarbon chain surfactants. The adsorbing rate at the air/water interface became slow with an increase of the chain length. From the fluorescence intensity ratios of 373 and 384 nm using pyrene as a probe, for n = 8, 10, and 14, the pyrene was solubilized in surfactant micelles at around the cmc, whereas for n = 12 the pyrene was solubilized from a concentration of 10-fold the cmc. The scattering intensities by dynamic light scattering also increased from around these concentrations for each chain length, showing the formation of aggregates in solution.