Formation Of Homochiral Helical Nanostructures In Diblock Copolymers Under The Confinement Of Nanopores

The crucial organic molecules associated with life are chiral.The amino acids and sugars from proteins and nucleic acids exhibit homochirality,which is expected to be a key biosignature in living systems.However,the origin of homochirality in life remains mysterious though many efforts have been devoted to this topic.In addition,chirality has great potential applications in electronic manufacturing,biomedicine,optical devices and other aspects,and thus attracted tremendous attention from the scientific communities of biology,chemistry,physics,and materials.Helical structure is a typical chiral morphology and is ubiquitous in nature.How to control the chirality of helix,especially the helix formed in achiral systems,is a problem with important re-search significance.Studies have shown that achiral block copolymers can self-assemble into helical structures confined in nanopores.Nonetheless,the helical structures possess random chirality selection,i.e.equal proba-bility of left-handedness and right-handedness.However,the chirality of helical structures is readily controlled by imposing proper external chiral conditions due to the intrinsic soft property of block copolymers,which offers a simple but efficient model for the study of chiral selection of helix.In this thesis,the external condition with chirality is introduced into the cylindrical confinement,and the stimulus response of the chiral selection of self-assembled morphologies from achiral macromolecules to external conditions is systematically studied from the thermodynamics by using the self-consistent field theory.In chapter one,we briefly introduced block copolymers and reviewed the research progress in this field.In chapter two,we introduced two reliable and commonly used theoretical and simulation methods on block copolymers researching,i.e.self-consistent field theory(SCFT)and the time-dependent Ginzburg-Landau theorv(TDGL).In chapter three,we proposed a method for the chiral control of helical structures by introducing spirally-arranged patches into a nanopore.The self-assembly of simple achiral AB diblock copolymers confined in a nanopore with spirally arranged patches on its inner surface was studied by SCFT.We calculated the free energy difference of the single-helical structures with different handedness.Moreover,we simulated the self-assembly process using an iterative process of SCFT solution starting from a disordered state,and counted the formation probability of different helical structures.We found that the formation probability of the homochiral helix with favorable free energy increases rapidly,leading to the conclusion that a minuscule difference of 0.5 N1.0 x 10-4 kB Tper chain is enough to obtain the homochiral helix by suppressing its counterpart of a higher free energy.However,for a stronger chiral guiding field,other homochiral helical structures with unfavorable handedness and thus increasingly higher free energy become more likely to be formed.Morphological snapshots during the self-assembly process reveal that the formation of these metastable helical structures is induced by their kinetic pathways,which are altered to be favorable by the strong chiral field of the patch pattern.Therefore,our work suggests that both thermodynamics and kinetics are important for controlling the chirality of helical structures.In the fourth chapter,we discussed the effectiveness of chiral pattern and tried to give the design principle of the chiral guiding patterns.Firstly,we studied the matching degree between helical structures and chiral guiding field by adjusting the patch positions,and examined the effect of the matching degree on chiral selection of helical structures.The results show that the inducing effect of chiral patterns has a certain tolerance,that is,when patterns as a whole deviate from the ideal position to a certain extent,the chiral guiding field still exhibits good induction ability.In addition,while the distance between patches exceeds a certain range,the ability of pattern induction decreases rapidly,which indicates that the pattern distribution with a good directed effect has a threshold value for their spacing.Based on these analyses,we deduced the design principle of chiral patterns on the surface of nanopores.The validity of this principle was verified by TDGL and SCFT from two aspects of dynamics and thermodynamics.It will have important significance for the preparation of helical structures with homochirality in experiments.The fifth chapter gave a summary.