Study On The Surfactant In Aqueous Solutions By Ultramicroelectrode Voltammetry

Surfactants are widely used in various fields and becoming necessary additive in industrial production and people's daily life due to their unique properties. In recent years, the new generation of surfactant, Gemini surfactant, is becoming the researching hotspot of relative fields. The Gemini surfactant improves the structure of traditional surfactant and performs better property than the traditional surfactant. The research ranges from its structure design, composition and analysis to interface activity, quality of the congeries, cooperating effect and application, etc. Therefore, it's importance to develop new researching methods to study the performance, functioning rule and principle of the surfactants.Based on the existing researches, this work enlarges the application of the ultamicroelectrode voltammetry in the surfactant system, mainly its application in research of the quality of traditional surfactants and Gemini surfactant. The ultamicroelectrode voltammetry is used to measure the diffusion coefficient change of micelle, the effect of the additives on the quality of the surfactant solution is specially studied. The study includes interface tension, micelle shape, size, diffuse and interaction, relative rules and mechanism are discussed, and a deeper comprehension of the microcosmic structure change of the congeries and some important property is realized.The main contents and the results are as follows:1. The effects of catechol on the change of cetyltrimethylammonium bromide (CTAB) micelles in aqueous solutions have been studied by Ultramicroelectrode (UME) cyclic voltammetry and Time-Resolved Fluorescence Quenching (TRFQ). It has been shown that the diffusion coefficient decreases and the micelle aggregation number increases with the addition of catechol. In order to analyze the change of the micelles, other micelle parameters like the effective radius (a), surface area of micelle (S), area of single CTAB molecule (A) and packing parameter (P) were calculated. All the results show that catechol can accelerate the increase of the aggregate size and sphere-to-rod morphology change of CTAB micelles even with lower concentration of CTAB.2. The effects of NaCl on the properties of alkylbenzene sulfonate Gemini surfactant have been investigated by spinning drop method and Ultramicroelectrode (UME) cyclic voltammetry. Spinning drop method and UME are used to measure the interfacial tension between Gemini Ia aqueous solution and heptane, the diffusion coefficient of Ia in aqueous solutions. It has been shown that the interfacial tension decreases and the diffusion coefficient increases with the addition of Nacl. This is because that electrostatic force reduces the electrostatic repulsion forces between ionic groups of Ia, which leads to a tighter arrangement of Ia and then reduces the interfacial tension and diminishes the size of micelles; micelles surface charge has been neutralized, so the electrostatic repulsion force between micelles decreases and the mobility of the micelles increases, which shows a larger diffusion coefficient.