Phase Behaviors Of Self-assembled Helical Polyelectrolyte In Aqueous Solution

Self-assembling polyelectrolytes are formed by small-molecular unit through weak interaction which will ionize into surface charged polyion and counter-ions with opposite charge in aqueous solution.Self-assembling helical polyelectrolytes,namely,ionic self-assemblies with helical formation,not only maintain the character of self-assembling polymers but also with unique helical charge distribution and rotational degree of helical symmetry.It can serve as an unique model system to research non-trivial polyelectrolyte interaction and phase behaviors.On the other hand because they are similar to the biological macromolecular such as DNA they have widely attracted researchers ' attention.However numerous work about self-assembling polymers mostly refer to primary assembly and research on how the self-assemblies further arranged into long-range order structure and determining factors are still in embryo.Based on the background,in this thesis we systematically explore the charged helical self-assembling nanotubes' meso-phase behaviors in dilute solution,the mechanism and driving force under the arrangement of the charged helical nanotubes into highly ordered rectangular structure and the counter-ions effect on the rectangular structure in aqueous solution.The main works and results in this dissertation are summarized as follows:1.The charged supra-molecular helical nanotubes' meso-phase behaviors and the response of the meso-phase to aging time and additional salts are investigated in dilute solutions.The nanotubes can spontaneously pack into a transient phase with liquid-like positional order termed hexatic.The hexatic phase will transform into a stable rectangular phase by increase aging time or introducing NaCl to the solution.The hexatic phase is sensitived to the original solution state such as concentration and types of counter-ions.The angular correlation or relative rotation between neighboring nanotubes originates from the helical charge pattern and are responsible for the meso-phase behaviors.In contrast to the transient hexatic phase,the equilibrium structure is rather robust regardless of the salt concentration and ion type.Compared to biological macromolecules and colloidal crystal,the slow crystallization kinetics and the stable thermodynamic equilibrium may open a new sight to solution preparation of crystalline materials.Those result not only help to understand the phase behaviors of helical polyelectrolytes but also offer guidance to soft-matter assembling in solution.2.The mechanism of long-range ordering and crystallization kinetics of supra-molecular helical nanotubes are systematically investigated.The effect of original solution's concentration on the crystallization kinetics of helical nanotubes are monitored by SAXS.The essential role of counter-ions in the helical nanotubes'crystallization is explored by SANS.The helical nano tubes go through three stage forming the unique rectangular phase.They first arrange into a hexatic phase with neither long-range position order nor angular order and then the precursor rectangular are formed form by deforming the hexatic structure to reduce the angular frustration.After that by further rotation along the axis of the helical nanotubes,the rectangular structure is improved into a three dimensional more order structure with angular correlation.3.Different counter-ions,effect on the aggregation behaviors of highly charged and condensed supra-molecular nanotubes are compared.Explicitly opposite counter-ions,effect on the rectangular bundles were observed in aqueous solutions of chlorides and hydroxides.The hydrophobic TAA+ cations with large diameter,and less affinity to the surface charged-COO-groups induced isotropic compression and distorted the order of the bundles.However,smaller hydrophlic M+ counter-ions with stronger affinity to the surface charged group induced anisotropic expansion.The specific counter-ions effect can further influence the pH values of the mixture solution.The results contributed to the rational design of metallogels as well as other functional supramolecular materials.