Double Liquid Crystalline Block Copolymers And Their Blends:Synthesis,Phase Structures And Self-assembly Behavior

Liquid crystalline(LC)block copolymer is a fascinating candidate for advanced functional materials.The coupling of liquid crystalline order and micro-phase separation of block copolymer could potentially enrich the phase behavior of the hierarchical nanostructures.In this work,for the first time we have successfully synthesized a series of narrow dispersed(PDI<1.10),well-defined polyether based LC homoplymer and diblock copolymer composing different prototypical LC phases via anionic ring-opening polymerization.The LC block copolymer based hybrid materials are also fabricated with rational design.In this thesis,we systematically investigate the self-assembly behavior these LC polymeric soft materials in bulk,solution and thin film state by means of thermal analysis,X-ray scattering,Transmission electron microscopy(TEM)and simulation of the reconstructed lattice.We have discovered a series of novel nano-phase separated superstructures in block copolymer and elucidated the effect of size incommensuration and nano confinement to the structural and phase behavior of the LC orderings and the multiscale nano structures.The delicate control of the LC block copolymer in nanopatterning is also realized.Rational design and successful synthesis of a novel double side-chain LC diblock copolymer bearing the same flexible polyether backbone were achieved via sequential anionic polymerization.Although the building blocks are of the same smectic phase,symmetry and orientation,we have demonstrated that the tiny size(?3 ?)incommensurateness of phase structures across the interface could result in the competition of LC ordering.We have found that the strong LC field of one block could prohibit the formation of LC phase of the adjacent block.Moreover,it is observed that the existing LC phase can be disrupted with the evolution of the dominating LC field of the neighbouring block.Release of constraint from the dominating LC field by isotropization allows the development of the suppressed LC phase.This work highlighting the crucial role of size incommensuration effect in the self-assembly of the LC based soft matters.By artfully utilizing sequential anionic polymerization,we have acquired flexible double LC diblock copolymers composing different prototypical LC phases,semctics and nematics,which process different symmetries,orderings and modulus.Thermodynamics equilibrium hierarchical superstructures with orthorhombic and pseudo-hexagonal symmetries in block copolymers are discovered by introducing the competition of anisotropy attributed from liquid crystalline ordering and nano-phase separation.We demonstrate that the stretched N tethers,projected regularly from the S layers,could transfer the local organization and guide the correlated assembly.The strategy of utilizing anisotropic and soft featured LC interactions are suggested to contruct novel complex structures in block copolymers.The thermodynamics immiscible LC phases among the S and N,together with the huge polarity difference between the chemical structures of these mesogenic groups,could drive the S-N system to self-assemble into the nanostructures on sub 10 nano-scale.By tuning the composition of the building blocks in diblock copolymers,coexistence of smectic and nematic orders in 3D curvaceous bicontinuous cubic or body center cubic structures are observed in S-N system with as few as ?22 repeat units.The incompatibility of the symmetries between the curvaceous nanostructures and the LC orderings,lead to the frustrated smectic packing in both bicontinuous network and nano spheres.Our experimental work set out a new theoretical challenges to understand the relationship between geometrical frustration and LC orders.Rich phase structures and evolutions of the blends of S-N liquid crystalline diblock copolymers and a nematic solvent(5CB)are investigated in a concentrated regime.This type of fully LC systems are macroscopically homogeneous with ordered phase separated structures on nanometer scale.By varying the temperature as well as the content of 5CB,the phase diagram of the blends is constructed,where the order-to-order transition(OOT)between lamellar and cylindrical nanostructures can be induced either lyotropically or thermotropically.The temperature and concentration dual-responsive properties are found to be closely related to the selectivity and distribution of 5CB,in addition to its phase transformation at the nematic-isotropic transition.As inferred from the miscibility and phase behaviors of its blends with the respective smectic and nematic homopolymers,the partition of 5CB in the S-N diblock copolymers and its influence on the phase structures reveal the important role of the LC interactions on the self-assembly of the diblock copolymers.The influence of surface energy discrepancy between the building blocks to the nanopatterning in S-N/5CB thin film is well studied.We have found that the directional LC anchoring and the LC interactions play a crucial role in determining the LC orientation and nanostructure alignment in this kind of soft material.The controllable alignment of nanostructues in LC block copolymer thin film is also realized.