Study On The Construction And Agglomeration Behavior Of Super - Amphiphilic Molecules Driven By Electrostatic Force

Gemini surfactants are a new kind of surfactant molecules. It has a lot of unique properties compared to conventional single-chain surfactant. However, the synthetic progress for conventional, covalently linked Gemini surfactant is quite tedious and time-consuming which greatly hindered the development and application of Gemini surfactant. At present, supramolecular amphiphiles, which refer to amphiphiles formed by noncovalent interactions including hydrogen bonding, electrostatic interactions, hydrophobic interaction, π – π stacking and metal-ligand complexation have become a hot theme. The noncovalent method avoids the complicated synthesis and purification process and realizes the efficient utilization of primitives.Electrostatic interaction has the advantages of simplicity, reliability and flexibility compared to other noncovalent interactions. Therefore, supramolecular amphiphiles driven by electrostatic interaction have attracted extensive attention.In this dissertation, a class of Gemini supramolecular amphiphiles driven by electrostatic interaction was designed and synthesized. Various techniques including cryogenic transmission electron microscopy(cryo-TEM), freeze fracture transmission electron microscopy(FF-TEM), small angle X-ray scattering(SAXS) and rheology are employed to investigate the self-assembly properties and microstructures of Gemini supramolecular amphiphiles in water. This study not only provides ideal materials for surfactant structure-activity relationship, but also provides a new thinking for constructing new surfactants with excellent performance. The dissertation mainly contains five sections.In chapter I, the concept and properties of surfactants, the application and development of anionic/cationic mixed surfactants are briefly introduced. The research progress of Gemini surfactant and amphiphilic molecules are introduced in detail. Finally, the research content and significance of this doctoral dissertation are pointed.In chapter II, we investigated the phase behavior, microstructures and rheological properties of a salt-free surfactant mixture formed by bola-type dicarboxylic acid(sebacic acid, SA) and zwitterionic surfactant tetradecyldimethylamine oxide(C14DMAO) in water. The research shows the existence of strong synergistic effects between SA and C14 DMAO in interfacial adsorption and self-assembly in water. 1H NMR proves that a kind of electrostatically and hydrogen bonding-driven pseudo-gemini surfactant can form by the mixture of SA and C14 DMAO molecules at a molar ratio of 1:2, denoted as C14-S-C14. C14-S-C14 exhibits rich phase behavior in water and forms birefringent lamellar phases. Various techniques including FF-TEM、cryo-TEM and SAXS et al. are employed to investigate the microstructures of typical lamellar phase samples, hyper-branched bilayers have been discovered for the first time which may be due to the freedom of C14-S-C14 in molecular packing. The hyper-branched bilayers are sensitive to the concentration of surfactant, shearing stress and temperature.In chapter III, we studied a new salt-free SISA system by using a phosphoric acid which bears hyper-branched alkyl chains(DEHPA) and a bola-type strong alkali dication(HMO(OH)2). Ionically self-assembled complexes form between DEHPA and HMO(OH)2 through acid-base neutralization. The ionically self-assembled complexes exhibit good performance in surface activity. Birefringent Lα phases form in slight excess of DEHPA. At ρ = 2.4, the self-assembly behavior was found to be concentration dependent and rather sophisticated. Open or closed faults and closely-stacked flat structures which look like foams or cellular networks as well as many other microstructures have been distinguished, some of which can coexistent in the same sample. Multilamellar vesicles with highly flexible and even branched bilayers were detected at ρ = 2.6 and 2.8. Transitions from isotropic L1 phases to birefringent Lα phases can be induced by the addition of NaCl, which significantly increases the critical packing parameter p by suppressing the effective area of the hydrophilic headgroups of the ionic complexes.In chapter IV, we investigated the phase behaviors and rheology properties of DEHPA/LiOH/H2 O 、 DEHPA/NaOH/H2 O and DEHPA/KOH/H2 O three systems.Compared with the fatty acid vesicles reported in the literature, the concentration of acid and alkali required to form vesicles is larger and the pH ranges of vesiclesformation is wider in these systems. Through FF-TEM observation found that closely packed vesicles form in the three systems. The viscoelasticity of the vesicles is higher and sensitive to the total concentration and mixing ratio of acid and alkali.In chapter V, we investigated the aggregation behavior of surfactant mixture formed by cationic surfactant(tetradecyltrimethylammonium hydroxide, TTAOH)and long-chain fatty acid(FA) at air/water interface. The effects of surfactant concentration, the molar ratio of TTAOH and FA, temperature, the carbon chain length of fatty acid and oscillating frequencies on the aggregation behavior were investigated. The studies found that the addition of fatty acid improved the surface activity of TTAOH. The larger the content of fatty acid and the longer the carbon chain length of fatty aicd, the higher the surface activity of TTAOH/FA mixed systems.The interface layer of TTAOH/FA systems is dominant for elastic modulus. The elastic modulus of TTAOH/OA system is less than that of TTAOH, but the elastic modulus of TTAOH/DA and TTAOH/LA systems are larger than that of TTAOH. The order of the elastic modulus at the same oscillating frequencies and nTTAOH/nFA is as follows: TTAOH/LA > TTAOH/DA > TTAOH/OA.