The Synthesis Of New Carboxylate Gemini Surfactants And Their Micellization Character

New surfactant molecules are unremittingly appearing on account of the large research work aimed at increasing the performance of surfactant formulations. Comparing to ordinary surfactants which have single hydrophobic and single hydrophilic group per molecule, Gemini surfactants are made up of two amphiphilic moieties connected at the level of the head groups by a spacer group. Most research work have manifested that Gemini surfactants have higher performance than ordinary surfactants. It also makes prospective that we can control the delicate mutual forces at the level of molecule by changing the structure of Gemini surfactants, and as a result it will bring about interesting rheological properties. Owing to this, studies on the novel surfactants have attracted considerable attention in surface chemistry domain.To starting the research work, it is crucial to design and synthesize appropriate Gemini surfactants first. Generally, the methods used to synthesize Gemini surfactants are as follow: ①chose or design an appropriate coupling agent, then introduce two hydrophobic groups and two hydrophilic groups sequentially into the coupling agent; ②chose or design an appropriate coupling agent, then introduce two hydrophilic groups and two hydrophobic groups sequentially into the coupling agent; ③chose or design an appropriate amphiphilic molecule, then use a coupling agent to link the two amphiphilic molecules. In fact, selecting an appropriate material may simplify the synthesis route. But no matter what route you should chose, the intermediate must provide active parts for further reaction, and the active parts should be close to the joint of the hydrophobic group, the hydrophilic group and the spacer group. This is a key point when we consider designing the synthesis route or selecting the starting material.Until now, the synthesis of the carboxylate Gemini surfactants appearing on the literature only adopted method ① and ②. In this thesis, we adopt method ③: Start fromlong-chain fatty acids, use Hell-Volhard-Zelinsky α-Halogenation of fatty acid to prepare the intermediate (α-brominated fatty acids), then react the intermediate with the coupling agent (Benzene-1,4-diol; Ethane-1,2-diol; Butane-1,4-diol; Ethane-1,2-dithiol) via Williamson synthesis of ether, finally a series of carboxylate Gemini surfactants are obtained. In total, the synthesis route has the merits that the materials are in abundance and the route is shortcut.In this thesis, totally six kind of new carboxylate Gemini surfactants are synthesized. All products are characterized by elementary analysis, IR spectra and 1H-NMR spectra. Their structures are as follow:Also the critical micelle concentration and the counterion ionic association degree are determined. Based on mass action model, the Gibbs free energy, enthalpy and entropy changes in the process of micellization are evaluated. The values of cmc of the carboxylate Gemini surfactants are about one order of magnitude lower than the surfactant with single chain and single carboxylate group, showing that the Gemini surfactants are more efficient in forming micelle. It is also confirmed by the fact that the values of Gibbs free energy change of the Gemini surfactants are smaller than ordinary surfactants. On the other hand, the values of －T(Som are smaller than that of (Hmo , showing that the micellization is an entropy-driven process. Besides the enthalpy-entropy compensation phenomena are also investigated.