Synthesis And The Solution Properties Of Gemini Surfactants With Five-membered Heterocyclic Head Group

Gemini surfactants, which are the new type of surfactant, have attracted much attention in recent years. Due to their special molecular structures, Gemini surfactants are often superior to the corresponding single tailed partners in various properties, such as higher surface activity, lower critical micelle concentration, rich aggregation behavior, lower Krafft points etc. Because surfactants are widely used in scientific research and practical application, synthesis of some new Gemini surfactants with special structure has become a hot research topic in the field of chemistry, biological and materials. For the regulation the structure in molecular, two types of Gemini surfactants with five-membered heterocyclic headgroups have been synthesized:one is the cationic Gemini surfactants with pyrrolidinium headgroups, the other one is the pH sensitive Gemini surfactants with imide headgroups. The aqueous solution and monolayer were studied by employing various techniques, such as surface tension, fluorescence, conductivity, dynamic light scattering, cryo-transmission electron microscopy (cryo-TEM), and dilatational rheological. This thesis is organised into six parts.In the first section, the history, synthesis, the special properties and application of Gemini surfactants are summarized. It was be found that the synthesis of novel Gemini surfactant is necessary, which provided a basis to carry out this thesis.In the second section, two types of Gemini surfactants with five-membered heterocyclic headgroups have been synthesized:one is the cationic Gemini surfactants with pyrrolidinium headgroups, the other one is the pH sensitive Gemini surfactants with imide headgroups. All the products were characterized by the methods of NMR, ESI-MS, POM and EA. The results show that all the products are object and have highly purity.In the third section, we investigated the surface activity and micellization of Gemini surfactants Cn-4-nPB (n=10,12,14,16) in aqueous solutions by employing various techniques such as surface tension, fluorescence, and conductivity. It can be found that Gemini surfactants Cn-4-nPB with heterocyclic head group had higher surface activity when compared with the m-s-m (CsH2s+1-α,ω-(CmH2m+1N+(CH3)2)2) type Gemini surfactants. It also can be found that the hydrophobic tails had significant effects on the micellization:the micellization is mainly entropy driven in the surfactant with shorter hydrophobic chain length (n＝10,12,14) but enthalpy driven in the surfactant with longer hydrophobic chain length (n=16).In the fourth section, we used surface tension, fluorescence and conductivity and studied the surface activity and micelliaztion of the Gemini surfactants C12-S-12PB with different spacer chain length (s=3,4,6,8,10,12,14,16). It can be found that the properties of C12-S-12PB are different with m-s-m Gemini surfactants:the minimum average areas per surfactant molecule for C12-S-12PB are increased with increasing spacer chain length. It can be explained by the limitations of the Gibbs adsorption formula. Through the surface tension, conductivity, fluorescent probe, UV visible spectrophotometer, dynamic light scattering and cryo-transmission electron microscopy measurements, it was found that the premicelle formation and double breakpoints exists in the solutions of C12-14-12PB and C12-16-12PB. It can be seen in the conductivity measurement that there is a significant difference of the effect of methylene groups in the hydrophobic tail and the spacer on the micellizationis.In the fifth section, we used π-A isotherms and expansion droplets to study the properties of monolayer and dilatational viscoelasticity of the C18-S-18PB (s=3,8,12). From the π-A isotherms, it can be found that all the monolayers of the surfactants used here are liquid core expanded film. The expansion droplet technology results show that the spacer length, disturbance frequency and surface pressure all affected dilatational viscoelasticity of the interfacial film.In the sixth section, we used pH titration, surface tension and fluorescent measurement to study the effects of the pH and hydrophobic tails on the surface activity and micellazation for the Gemini surfactants with imide headgroups. It was found that the aggregation transition in the aqueous solution was induced by pH.