Computer Simulations And Experimental Studies On The Ordered Molecular Assembly Based On Nonclassical Amphiphilic Molecules

The surfactants can be assembled into various aggregates in different solvents, including micelle, liquid crystal, vesicle, gel, and also the ordered aggregates in solid state. In the past years, the aggregation behaviors of traditional surfactants in different solvents were investigated in details. With the development of surfactant industry, the word surfactivity is involved in many other fields to define some untraditional surfactants and then people begin to investigate the aggregates formed from them. Getting more information on these non-classical surfactants can expand the aggregates species and also help us better understand the process of microphase separation. So the aggregates, including micelle, liquid crystal, vesicle, gel, and also the ordered aggregates in solid state, formed by several non-classical surfactants are investigated by both experimental and theoretical simulation methods in this dissertation. The studies can be divided into four parts.1. Investigations on the aggregates formed by long chained imidazolium salts. The work can be divided into two parts:investigations on the aggregation behavior of [C16mim]Cl in two different ionic liquids, EAN and [Omim]PF6, and then compared with that in water in order to make clear the solvent effect; Investigations on the gel phase formed in [C16mim]Cl/SDS/H2O ternary system. Following results can be obtained.(1) [C16mim]Cl can be assembled into micelle, hexagonal, and reverse bicontinous cubic phases in EAN, [Omim]PF6, and water. The threshold temperature of liquid crystalline (LC) phase formation increases in the order of water, EAN, and [Omim]PF6 but the areas of the LC phases display an opposite trend. This could be attributed to the different assembling abilities of [C16mim]Cl in these three solvents, which are quite related to their Gordon parameters. Meanwhile, the dissipative particle dynamics (DPD) method was used to simulate the phase behavior of [C16mim]Cl-EAN binary system at room temperature. Obtained results can give us microphase separation information which is much difficult to get by experimental methods. Such an investigation is quite important, which can help us better understand both similarities and differences among EAN, [Omim]PF6, and water or between [C16mim]Cl and traditional surfactants.(2) The ternary system SDS/[C16mim]Cl/H2O can form a novel gel phase at quite high water content. Results from rheology and POM measurements show that, the gel phase formed in the present system may be less ordered and has analogous rheological properties to that of vesicles formed in traditional systems. The sol-gel temperature can be ascertained by DSC technique. Control experiments and simulated results have certified that the complex formed by the [C16mim]Cl and SDS is dissimilar to that formed by the parallel catanionic surfactants with different head groups. Besides, the solvophobic interaction is also proved to play very important role in the gel phase formation. The phase behavior of this ternary system is quite different from those of previous ones, which had broken up the conventional phase behavior of catanionic systems and can help us better understand the special structure of the surface-active surfactant [Cnmim]Cl.2. Investigations on the aggregates formed by long chained piperidine salts CnPDB (n=12,14,16). The work can be divided into two parts:the micellization behavior of CnPDB in water were investigated by surface tension, conductivity, and fluorescence methods and then compared with that of long chained imidazolium, pyrrolidine, and traditional cationic surfactants; Investigations on the LLC phases formed by long chained piperidine salts CnPDB in water, both concentration and temperature effects were discussed in details. The following are obtained results.(1)The critical micelle concentration (cmc) value of CnPDB decreases with increasing alkyl chain length. Various thermodynamical parameters (ΔGm0,ΔHm0和ΔSm0) during the micelle formation process are calculated. The obtained results show that, the micelle formation process is entropy dominatant at low temperature while it is enthalpy dominated at high temperature. Meanwhile, the cmc value of CnPDB was compared with those of CnmimBr, CnTAB, and CnMPB. Obtained results show that, the cmc value of CnPDB is a little higher than CnmimBr but lower than CnTAB and CnMPB, which can be attributed to the following reasons:the alkyl chain length of CnPDB head group is longer than CnTAB and CnMPB, which is better for surface tension decrease; Even though the alkyl chain length of CnPDB head group is longer than CnmimBr, the conjugated bands in the later can increase the interactions between different molecules, which will result in lower cmc. Such an investigation can help us better understand the micellization behavior of CnPDB in water and also makes it clear for both the similarities and differences among various long chain ILs.(2) Through comparison of these three LC systems, it can be found that, for C12PDB/H2O system, only the H1 phase is observed and a Maxwell behavior is exhibited. However, both H1 and V2 can be identified in C14PDB/H2O and C16PDB/H2O systems and the H1 phase here shows a gel-like behavior, unlike the traditional cationic surfactants. Such different rheological properties for H1 phases in these systems inspire us to extend investigations to systems with other series of surfactive ionic liquids. Meanwhile, the structural and rheological parameters have been claculated. Obtained results show that, the surfactant molecules tend to arrange themselves more tightly with increasing temperature and concentration. Such investigations were a great supplement to previous reports on surfactive ionic liquid and can help us to better understand the LLC phases formed by the piperidine salts.3. Theoretical investigations on the aggregates formed by Pluronic polymers in water. The phase behaviors of Pluronic P123 or P104 in water were simulated by a mesoscopic method, MesoDyn and then compared with the experimental results in details; The effect of EO charge on the aggregation behavior was also explored. The following are obtained results.(1)With P123 concentration increasing, different aggregates including micelle, hexagonal and lamellar phases, are formed in P123-H2O binary system, which can reproduce most experimental phase regions and has proved the accuracy and responsibility of simulation results. The simulated phase ranges are more or less different from those established from experiment, especially at high polymer concentrations. This can be attributed to different phase mapping situations, i.e. the constant shear used in simulation vs. the varied external forces in experiment. The influences of PO block amount or P123 concentration on aggregate formation rate can be explored by the changing trend of order parameters with increasing time steps, which can present us the microphase separation information more directly. The mesoscopic simulation method is a valuable tool for the description of mesoscale morphology and can give us insight into the aggregates formation process, which will be a great supplement to the experimental results.(2) With the increase of P104 concentration, two different aggregates, hexagonal and lamellar phases, can be formed in aqueous solutions. The hexagonal phase becomes more and more ordered with the increase of charge per EO bead while lamellar phases display a quite different trend. With the increase of charge per EO bead, the lamellar phases first become more ordered, then it turns to be a reverse hexagonal phase and finally the structures become disordered. Such results can be attributed to the changing curvature of polymeric domains caused by both short range and electrostatic interactions. This simulation can help us predict the results of new series surfactants and is also a great supplement to previous investigations on the phase behavior of P104.4. A much facile ionic self-assembly (ISA) route was employed, through the complexation between a double-tailed anionic surfactant, aerosol AOT and a functional dye molecular Rhodamine B (RB), to fabricate the ordered aggregates in solid state. The effect of different experimental conditions, such as temperature, concentration, and the storage period were investigated. The optimum formation condition of the ordered aggregates, star-shape aggregate is obtained. Their properties and structures are characterized by different techniques. Obtained results show that, the stoichiometry between AOT and RB in the complexes is determined as a 1:1 molar ratio; The center of the complex is occupied by a circle dot while the surrounding is encircled by many sheets; The results from steady-state fluorescence and laser confocal microsopy indicate that, the formed complex is of great fluorescent properties and may have potential applications in some specific fields. A possible formation mechanism for the complex is also proposed.Thanks for the financial supports from the National Natural Science Foundation of China (No.20573066,20773080 and 20973104).