Self-Assembly Of Amphiphilic Oligo(Phenylene Vinylene)-b-Poly(Ethylene Oxide) Rod-Coil Block Oligomers At Interfaces

Rod-coil block molecules are a well self-assembling system to constructsupramolecular structures. Through the phase separation of the rod block and thecoil block, rod-coil block molecules can self-assembly into various nanostructures,where the rod block can align and orient orderly. As a matter of fact, the functionsof self-assembling structures formed by rod-coil block molecules are, to a largeextend, dependent of the molecular alignment and orientation on solid substrates.Especially when organic conjugated groups are incorporated into the rod-coilblock molecules as the rod block, utilizing the ordered alignment and orientationof the organic conjugated groups, they will present some special properties in themicroelectronic field, such as the field-effect transistors, nanowires, polarizedlight-emitting diodes and so on. Recent studies have confirmed that the thin-filmself-assembling structures and microscopic morphologies of rod-coil blockmolecules are not only related to the molecular structure and composition but alsorelated to the interfacial conditions. However, a comprehensive understanding ofthe self–assembling behaviors of rod–coil block molecules on solid substrates,such as their morphologies, structures, and molecular alignments, is still lacking.It is therefore crucial to explore the relationship of the thin–film morphologies andself–assembling structures of rod–coil block molecules on substrates withinterfacial conditions, which will provide experimental and theoreticalfoundations for self-assembling behaviors of rod-coil block molecules atinterfaces and further have important directed meaning and application values forfunctional materials. On the basis of the self-assembly idea, in this thesis, we synthesized a series ofamphiphlic rod-coil diblock oligomers (EOnOPV, n, the ethylene oxide unitnumber, = 3, 7, 12 and 16) containing the conjugated oligo(phenylene vinylene)(OPV) dimer as the rod segment and poly(ethylene oxide) (PEO) as the coilsegment and firstly studied their self-assembling behaviors and structures at theair-solid interface, the air-water interface, and the liquid-solid interface, as well asthe influence of the interfacial conditions on their self-assembling behaviors andstructures. At the air-solid interface, we investigated the influences of the interfacialconditions such as solvent evaporation and atmosphere humidy on the thin-filmmicroscopic morphologies and self-assembling structures of EOnOPV oligomerswith different PEO segments on hydrophilic substrates. It is found that the coillength, solvent evaporation and atmosphere humidity can exert an importantinfluence on the thin-film microscopic morphologies and self-assemblingstructures of EOnOPV oligomers. Under the condition of quick evaporation anddry atmosphere, utilizing the simply casting method, we obtained surfacecoverage-controlled monolayer structures on hydrophilic substrates. Increasingthe cast solute volume, EO12OPV and EO16OPV oligomers with the longer coilsegment can form polar lamellar structure packed in the head-to-tail fashion. But,under the condition of the slow evaporation and humid atmosphere, EO12OPVand EO16OPV oligomers can form the curved and long ribbon-like aggregateswith the symmetric bilayer structure. In all these structures, the OPV segmentscan align shoulder to shoulder through the π-πstacking interaction. We believethat at the air-solid interface, changing the interfacial conditions can adjust themicro-equilibrium among the interactions between the rod segments, the rod andcoil segment with the substrate and the atmosphere, which may lead to theformation of various self-assembling nanostructures. We also study the self-assembly of EOnOPV oligmers with different PEOsegments at the air-water interface. EO3OPV oligomers with the shortest PEOsegment can present a well Langmuir film property and form the close-packedmonolayer film. EO12OPV and EO16OPV oligomers with the longer PEO segmentcannot form closely packed monolayers but form the irregular-shaped aggregates.However, EO7OPV oligomer presents a well Langmuir film property and mayform aggregates with the regular shape and uniform size. Interestingly, utilizing the phase separation of the mixed Langmuir-Blodgett(LB) monolayer of EO7OPV and palmitic acid (PA), the rod-like aggregatesconsisting of EO7OPV with regular shape and uniform size can form. Adjustingthe EO7OPV/PA mixing molar ratio, we can obtain a series of EO7OPV rod-likeaggregates with different lengths. The length of the rod-like aggregates can becontrolled in a large range. We think that the formation of the rod-like aggregatesof EO7OPV originates from the long-range molecular oriented order driven by theπ-πstacking interaction between the OPV segments. In addition, these rod-likeaggregates can align along the K+ ions arrangement with the 6-folded symmetryon the crystalline surface of the mica during the transfer of the Langmuir film. Wepropose a two-step forming processes of the oriented rod-like aggregates on micasubstrates. For the mixed LB film of EO3OPV and PA, the elongated aggregates...