| As one of the most significant issues in the science of the21st century, molecular self-assembly, via non-covalent interactions, has been recognized as a fascinating, practical, bottom-up approach to achieve stable, structurally well-defined, and functional objects at the nano-and microscale in biological systems and materials synthesis. The current reports indicate that molecular self-assembly favors to occur in the solution and at the interface:(1) Self-assembly in solution is the process by which the amphiphilic molecules pack to form ordered aggregates by non-covalent interactions, such as micelles, vesicles, sponge structures and cubic structures. The amphiphilic molecules include lipids, surfactants, amphiphilic polymers and biomacromolecules, etc. The controlled assembly of amphiphiles in solution can be achieved by changing the molecular structures and the external conditions. Novel aggregates can be formed by varying the charges of the bilayers, which is also the hot research in soft matter chemistry.(2) Self-assembly at the interface is the process by which all kinds of molecules pack and assemble at gas/liquid, gas/solid, liquid/liquid, and liquid/solid interfaces. The interfacial assembly of multilevel films by various technologies, involving LB, breath figure method and chemical adsorption, can product film devices with special functions. In addition, the precise decoration of biological membranes or biocompatible interfaces can be performed by self-assembly, which helps to further understand the life systems and also provides a new approach to product new biomaterials for biological engineering. Therefore, molecular self-assembly has attracted much attention in chemistry, physics, biology, and material science.In this thesis, two issues were focused:(1) self-assembly of lamellar aggregates in surfactant solution, including disks, sponge, planar lamellas and vesicles;(2) formation of honeycomb-patterned porous structures of amphiphilic polymer at interface by breath figure method. We investigated the influence of various factors on the self-assembly and the structure transition, determined the ordered microstructures and their properties, discussed the formation mechanism and gave the theoretical consideration, and explored the functions and applications of these novel structures. It is expected that the research can reveal the theory of molecular self-assembly and the discipline of the structure transition, summarize the synergistic effect of various weak non-covalent forces in the equilibrium of variably-scaled multicomponent complex systems, and finally achieve the control of the microstructures and the functions. The outline and contents of this doctoral dissertation are as follows:Chapter I is a comprehensive introduction of the research background. The concepts and the differences of self-assembly and self-organization were determined firstly. Then the historical development of the colloid chemistry, nano science, soft matter and supramolecular chemistry as well as their relation was outlined in brief. The hot knowledge of surfactant physical chemistry includes the surfactant, weak non-covalent forces, and the theories of the aggregation formation. Particularly, the research status of the lamellar aggregates, the applications of vesicles in materials synthesis and the recent development of the honeycomb films by breath figure method were reviewed in detail. The objective and the scientific significance of this doctoral dissertation are also pointed out at the end of this part.In Chapter Ⅱ, the phase behavior, microstructures, the rheological behavior as well as the influences of salt and pH were investigated and compared in two double-chain anionic surfactant/nonionic surfactant aqueous systems, i.e., tetraethylene glycol monododecyl ether (C12EO4)/sodium bis(2-ethyl hexyl)sulfosuccinate (AOT) and C12EO4/bis(2-ethylhexyl) phosphate (HDEHP). The contrast advantage is that AOT and HDEHP have similar molecular configuration and area of head group. The membrane charge was confirmed to play a key role in the phase transition of the lamellar structures, which further provides a theoretical consideration for the self-assembly of onion-like vesicles driven by charges.(1) In the AOT/C12EO4/H2O system, an attractive net interaction exists between the two surfactant molecules and a negative interaction parameter values (βm and βs) indicate a synergism in the non-ideal mixing behavior. Onions, i.e., the densely packed multilamellar vesicles with uncountable bilayers are directly observed in a bluish sample solution by charging the swollen C12EO4lamellar phases with addition of AOT. The addition of AOT into nonionic lamellar phase, through electrostatic repulsion of the ionic headgroups, will suppress the Helfrich undulation and induce the transition from planar lamellas to vesicles. Interestingly, the addition of NaCl into the AOT/C12EO4system causes the phase transition from micelles to vesicles. As increasing the amount of salts, the bilayers of the lamellar phase exhibit more flexible due to the electrostatic shielding of electrolyte, along with a decrease of the solution viscosity and the viscoelasticity. It is believed that the charges act crucial roles in the flexibility of bilayer membranes. The obtained multilamellar architectures are facile for long-term storage of multiple components and can effectively slow their release.(2) In the HDEHP/C12EO4/H2O system, the addition of small amount of HDEHP into nonionic lamellar phase also induced the formation of vesicles, and the lamellar distance (d) decreased with the increase of HDEHP. A larger amount of HDEHP caused the increase of the d and subsequently leaded to the transition from vesicle phase to micelle/lamella two-phase. That is because excess HDEHP, just like the middle-chain alcohol, were solubilized in the vesicles, swelled the bilayers, and induced the phase separation. In addition, increasing the pH of HDEHP/C12EO4vesicle solution caused that the solution viscoelasticity and the stress force underwent a maximum value, and the d decreased firstly and then increased. A lamellar gel was formed at pH=3.78. This indicated that the membranes passed through a saturation of effective charge density with the pH.In Chapter Ⅲ, two metallosurfactants, calcium dodecyl sulfate (CDS) and Ferrum laurate (FeL3), were synthesized. The phase behavior and microstructures of these surfactants were studied in water and organic solvent, and normal and reversed vesicles were formed, respectively. Then the application of these vesicles in the materials synthesis were explored.(1) In the first part, the phase and temperature-dependent behavior of CDS/tetradecyltrimethylammonium bromide (TTABr)/H2O system with excess CaBr2was studied. At high temperature, a classic birefringent vesicle phase was observed in the TTABr-rich region while the precipitates in both the anion-rich and the cation-rich regions. This phase behavior is completely different with that of SDS/TTABr/H2O system. The introduction of the Ca2+ion was proposed to alter the electrostatic shielding of the surfactant headgroups. Then, the vesicles were used to prepare microcrystals of VH2O by adding dimethyl oxalate to vesicle solution. The production of brick-like (dodecahedrons) and star-like (icositetrahedrons) CaC2O4crystals indicated that the vesicles can play an important role in affecting the formation and growth of the crystals in solution synthesis.(2) In the second part, FeL3metallosurfactant can successfully self-assemble into reversed vesicles in organic media such as pure CHCI3and mixture solvent of CHCl3and CH3OH. Deformed solid vesicles, including collapsed erythrocyte-like and broken hollow shells, were obtained directly via drying selective organic solvents. This morphology was kept from reversed vesicles of metallosurfactant in organic media to hardly solid shells and it is ascribed to the evaporation rate of the solvents and the interactions between ferrum laurate and solvents. It is expected to expand the current considerations on the reversed vesicles and to demonstrate this kind of universal self-assembly phenomena in organic solvents. It also provides a facile strategy to modulate the deformation of the vesicles after the removal of the solvent and produce hollow shells.In Chapter IV, the phase behavior, microstructures, rheological properties as well as the influences of temperature and pH were investigated in two salt-free fatty acid/nonionic surfactant aqueous systems, i.e., perfluorolauric acid (PFLA)/C12EO4and lauric acid (LA)/C12EO4. The differences of the structures and properties of the self-assemblies induced by the CF-and CH-chains were compared in detail.(1) The PFLA/C12EO4mixture exhibits pronounced synergistic effects in mixed micellization and rheological properties. Only one type of mixed micelle is formed in the mixed dilute solution. At lower content of PFLA, with the increase of the total surfactant concentration, short thread-like micelles grow to form larger discs. After further addition of PFLA, due to that the fluctuant planar bilayers of nonionic C12EO4are charged, the vesicle gels spontaneously form comprised of densely packed unilamellar and multilamellar vesicles, in which the fluorocarbon chains in the bilayers are in a fluid state at room temperature. The elastic properties and the yield stress of the lamellar solution largely increase upon addition of small amounts of PFLA, and then pass through a maximum at a saturation of effective membrane charge density. Interestingly, increasing the pH of the gels causes a backward transition from stiff vesicles to flexible planar bilayers. As increasing pH, the bilayers exhibit more flexible due to the reduction of the membrane charges, along with a large decrease of the solution viscosity and the elastic properties. The combination of strong stability of the vesicle gels with the interconvertible transition of bilayers-vesicles is expected to be of practical function for controlled drug delivery and release.(2) The LA/C12EO4/H2O system exhibits rich phase behavior. At lower concentration of C12EO4, the concentration induced the spontaneous formation of vesicle phase and stable surfactant aqueous three-phase equilibria with coexisting forms. At higher C12EO4concentration, the lamellar liquid crystals were formed after the addition of LA. LA/C12EO4system showed a strong dependence on temperature and vesicle occurred in a narrow temperature range. Compared with LA/C12EO4system, PFLA and C12EO4exhibited stronger interaction and easier aggregation tendency, and can form stable vesicle gels. Furthermore, PFLA/C12EO4system owns a stronger resistance to the shearing and temperature, and is in favor of its application.In Chapter V, aqueous three-phase surfactant systems (A3PS) are important, multicomponent, stable three-phase equilibria with coexisting forms in a common colloid solution, but have been largely ignored regarding further characterization and application. We reported a new application for surfactant phase behavior and a general strategy for the assembly of A3PS by mixing simple, commercially available, single-tailed anionic/nonionic or anionic/cationic surfactants in water. The report also develops a better, more general understanding of the physical parameters needed to form and tailor the three-phase properties of such systems for different purposes. As with conventional aqueous two-phase systems (A2PS), the A3PS can be regarded as a new separation and extraction system for biomaterials and dyes. Here, the A3PS was also used as mild media for one-pot synthesis of multiscale CdS nanowires. Particularly, the A3PS does not change and simultaneously separates the CdS nanowires with the comparable size in one phase, which provides a facile strategy for collection of monodisperse nanomaterials. Furthermore, it also provides a potential strategy for synthesis with fewer purification steps, that is, during the reaction the resulting product is condensed in one phase while residual reactants or the coproducts are simultaneously separated into other phases.In Chapter VI, honeycomb-patterned polymer films with tuning pore sizes and regularity of ordered2-or3-dimensional hexagonal arrays have met with widespread interest in different areas, for instance, as separation and superhydrophobic materials in recent years. In this chapter,2D honeycomb-patterned films of amphiphilic ferrocenyl-based oligomer containing cholesterol as side-chains were prepared using breath figure method on solid surfaces and their surface wetting behaviors were tested. These films can be simply prepared by spreading mixture of polymer and organic solvents on solid surface under moist airflow and at air/water interface without any extra moist airflow. Ordered2D hexagonal array of pores over a large area and monodisperse pores in size distribution can be obtained by changing various influencing factors, including humidity, wet volume, concentration, selective solvent, and spreading method, which could provide a facile route to regulate the morphology of patterned porous films. The surface wetting behaviors indicate that higher hydrophobicity of the ferrocenyl-based oligomer honeycomb films can be obtained by modulating the pore size and regularity. The dimensionality nature of the honeycomb film, i.e., the array of pores varying from monolayer to multilayer structure, was studied in detail. A tentative model, including several key influencing parameters, is described to illustrate the varying layer numbers in the one film. The formation of multilayer structure is ascribed to the Marangoni convection, thermocapillary effects, wet thickness as well as evaporation speed. Furthermore, the honeycomb films with photoluminescence were fabricated by mixing NH2-terminal PS and diphenylamino-substituted terphenyls in CS2. Then the pincushion structures were fabricated by peeling off the top surface of the honeycomb film, and exhibited superhydrophobic property. It is expected that this can promote the potential application of ordered porous polymer films in hydrophobic materials and biochemistry.In Chapter VII, we reported a new, simple strategy to apply honeycomb films for patterning of colloidal particles. By combination of "bottom-up" breath figure method and the electrochemical properties of the honeycomb oligomer film, hierarchically ordered hybrid membranes with ring-like patterning of Ag nanoparticles (NPs) anchored at the edge of the micropores have been fabricated. The attachment, shape, and distribution of Ag NPs have been investigated. One interesting phenomenon is that the nucleation and adsorption of Ag dots occurred preferentially at the edges of the micropores. The hybrid membranes exhibited rich electrochemical activities towards reduction of iodate ions and effectively enhanced the catalytic reduction of organic dyes. We believe that this method can be used to decorate and/or assemble functional metal NPs such as Au, Pd, and Cu on honeycomb-patterned surface and is exploited in photonics, sensors, and catalysis. |
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