Abstract
We found that poly(γ-benzyl-L-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) rod-coil block copolymers and polystyrene (PS) homopolymers can cooperatively self-assemble into nano-spheres with striped patterns on their surfaces (strip-pattern-spheres) in aqueous solution. With assistance of dissipative particle dynamics simulation, it is discovered that the PS homopolymers form a spherical template core and the PBLG-b-PEG block copolymers assemble into striped patterns on the spherical surface. The hydrophobic PBLG rods are packed orderly in the strips, while the hydrophilic PEG blocks stabilize the strip-pattern-spheres in solution. Defects such as dislocations and disclinations can be observed in the striped patterns. Self-assembling temperature and sphere radius are found to affect defect densities in the striped patterns. A possible mechanism is proposed to illustrate how PBLG-b-PEG and PS cooperatively self-assemble into hierarchical spheres with striped patterns on surfaces.
Highlights
In a preliminary work, we have discovered that rod-coil block copolymer poly(γ-benzyl-L-glutamate)block-poly(ethylene glycol) (PBLG-b-PEG) and rigid homopolymer poly(γ-benzyl-L-glutamate) (PBLG) could cooperatively self-assemble into super-helical structures with uniform chirality and screw-pitch in solution[16,17,18]
When selective solvent was added to the initial solution, PS homopolymers could firstly aggregate into spheres due to the lower Critical water content (CWC) compared with that of PBLG-b-PEG block copolymers
Critical water content (CWC), an indication for the onset of aggregation, was measured according to the method described in reference 54 From the turbidity curves (Fig. 6a), we found that the CWC of PS and PBLG-b-PEG are 9.1 vol% and 14.4 vol%, respectively
Summary
We have discovered that rod-coil block copolymer poly(γ-benzyl-L-glutamate)block-poly(ethylene glycol) (PBLG-b-PEG) and rigid homopolymer poly(γ-benzyl-L-glutamate) (PBLG) could cooperatively self-assemble into super-helical structures with uniform chirality and screw-pitch in solution[16,17,18]. Replacing the rigid homo-PBLG by homo-PS, the mixtures of PBLG-b-PEG and homo-PS self-assembled into spherical structures with striped patterns on their surfaces (strip-pattern-spheres) which are like “wool balls”. In this case, the PS homopolymers may form spherical templates and the PBLG-b-PEG block copolymers self-assemble into striped patterns on the template surfaces. Simulations based on dissipative particle dynamics (DPD) method were carried out, providing more detailed information about the self-assemblies, which could not be obtained experimentally because of the limitation of characterization methods Influencing parameters such as interaction between rod and solvent (aRS) and sphere radius (R) were further explored to verify the results theoretically. A possible mechanism was proposed to illustrate the self-assembly behavior of PBLG-b-PEG/PS mixtures
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