Abstract
A group of Gemini quaternary ammonium surfactants with the formula CnH2n+1CONH(CH2)2N+(CH3)2(CH2)2N+(CH3)2(CH2)2 NHCOCnH2n+1 · 2Y (n = 11, 13 and 15, Y = HCOO−, CH3COO− and CH3CHOHCOO−) have been synthesized by a counterion conversion process and characterized by Fourier transform infrared spectroscopy and mass spectroscopy. Their adsorption and self-aggregation properties are investigated by surface tension, conductivity, dynamic light scattering and transmission electron microscopy (TEM) measurements. The results show that these surfactants reduce the surface tension of water to a minimum value of 26.51 mN m−1 at a concentration of 5.72 × 10−2 mmol l−1. Furthermore, the increased alkyl chain length of the carboxylic counterions leads to the increased critical micelle concentration, the decreased degree of counterion binding (β) and the decreased self-assembly tendency, but the minimum area per surfactant molecule (Amin) adsorbed at the air–aqueous solution are similar. TEM images reveal that these surfactants self-assemble spontaneously into aggregates with vesicle or bilayer structures. It is also found that they have superior antibacterial activity at a concentration of 0.1 g l−1. The high surface activity and high antibacterial activity of the Gemini quaternary ammonium salt surfactants containing different carboxylic counterions bring more possibilities for the application in the field of biomedicine.
Highlights
Ionic surfactants are widely used in chemistry, material science, biochemistry and life science due to their unique interfacial adsorption and self-assembly behaviour
The Krafft temperature of these surfactants is determined from the plot of the specific conductance (κ) versus temperature in the aqueous solution
Seen from electronic supplementary material, figure S2, in the relatively low temperature range, the conductance of the surfactant solution has a small change with the increase of the temperature, and the sharp increase is observed within a relatively narrow temperature range that represents the sharp increase in surfactant solubility
Summary
Ionic surfactants are widely used in chemistry, material science, biochemistry and life science due to their unique interfacial adsorption and self-assembly behaviour. Anionic surfactants are often used in thickening, emulsification, decontamination and other aspects of research [1,2]. More and more novel surfactant systems and their applications have been reported [3]. Compared with other types of surfactants, cationic surfactants have two significant characteristics: they are highly bactericidal and adsorbed on the general solid surface. Quaternary ammonium surfactants, as a kind of important cationic surfactant, are usually used in antistatic, corrosion inhibition, sterilization and other aspects due to their molecular structure of positive charge head group [4,5,6]. Cationic surfactant–DNA particles are frequently used in the biochemical research and have promising prospects for application in the field of biochemistry [7,8,9]
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