Nanoscale hierarchical phase behavior of liquid crystalline block copolymers.

摘要

Self assembly of block copolymers (BCPs) is a bottom-up technique for manufacturing nanostructures with precision and efficiency. Hierarchy in structure and functionality can be achieved in BCPs by combining two classes of soft matter (BCPs and liquid crystalline polymers (LCPs)), which form ordered structures at different length scales, into a single phase system. Ensembles of nanostructures ranging from few nanometers to micrometers can be achieved. Three methods that have varying flexibility in terms of structure and functionality have been used to introduce LCPs into BCPs. The first part of the research focused on the characterization of phase structures of mesogen-jacketed LCPs that form rigid macromolecular columns within which the mesogens were aligned at an angle to the polymer backbone. A series of samples were investigated and the influence of molecular weight (Mn) and volume fraction ( f) on the overall phase behavior was studied in both low Mn and high Mn systems and symmetric/asymmetric systems. After establishing the phase behavior of MJ-LCBCP system, the second part of the thesis was focused on changing the diameter and surface chemistry of the macromolecular columns. The diameter was increased by changing the three-ring mesogen into a five-ring mesogen and the surface chemistry was altered by introducing alkyl tails along to the mesogens. This led to the formation of core-shell MJ-LCBCP system formed by the mesogenic core and alkyl tails. Within this system, the influence of f on the final phase morphology was studied in symmetric/asymmetric samples. The final part of the thesis was focused on the influence of improving the flexibility of the mesogen. Accordingly, both SC-LCBCP and H-bonded LCBCPs were studied. In the SC-LCBCPs, 12 carbon spacers were used to decouple the interactions between the mesogen and polymer backbone whereas in the H-bonded system, interactions between terminal-OH group of mesogen and nitrogen of the pyridine block were exploited to achieve the H-bond. The influence of fLC on the final phase structures was studied in both these systems. Detailed structural characterization results are presented that emphasize the unique phase behavior of these advanced materials.