Abstract
Self-assembly behavior of a mixture system containing rod-coil block copolymers and rigid homopolymers was investigated by using Brownian dynamics simulations. The morphologies of formed hierarchical self-assemblies were found to be dependent on the Lennard-Jones (LJ) interaction εRR between rod blocks, lengths of rod and coil blocks in copolymer, and mixture ratio of block copolymers to homopolymers. As the εRR value decreases, the self-assembled structures of mixtures are transformed from an abacus-like structure to a helical structure, to a plain fiber, and finally are broken into unimers. The order parameter of rod blocks was calculated to confirm the structure transition. Through varying the length of rod and coil blocks, the regions of thermodynamic stability of abacus, helix, plain fiber, and unimers were mapped. Moreover, it was discovered that two levels of rod block ordering exist in the helices. The block copolymers are helically wrapped on the homopolymer bundles to form helical string, while the rod blocks are twistingly packed inside the string. In addition, the simulation results are in good agreement with experimental observations. The present work reveals the mechanism behind the formation of helical (experimentally super-helical) structures and may provide useful information for design and preparation of the complex structures.
Highlights
Amphiphilic block copolymers have a capability to self-assemble into ordered nanostructures in selective solvents, such as spherical micelles, cylindrical micelles, and vesicles[1,2,3,4]
We studied the self-assembly behavior of mixture systems containing poly(γ-benzyl-L-glutamate)-b-poly(ethylene glycol) (PBLG-b-PEG) block copolymers and PBLG-g-PEG graft copolymers[22]
The experiments revealed that the PBLG homopolymers packed side-by-side to form bundles, and the PBLG-b-PEG block copolymers wrapped on the homopolymer bundles
Summary
Amphiphilic block copolymers have a capability to self-assemble into ordered nanostructures in selective solvents, such as spherical micelles, cylindrical micelles, and vesicles[1,2,3,4]. We have carried out a preliminary study on the self-assembly behavior of PBLG-b-PEG/PBLG mixtures in aqueous solution.[25] The experiments revealed that the PBLG homopolymers packed side-by-side to form bundles, and the PBLG-b-PEG block copolymers wrapped on the homopolymer bundles Supramolecular structures such as abacus-like (beads-on-wire) structures, super-helices, and plain fibers can be sequentially observed as the self-assembling temperature decreases. Twisting string and disk micelles were observed[41] Such success of the BD simulation made it to be successfully extended to examine the self-assembly behavior of rod-coil block copolymer/rigid homopolymer mixtures[25]. Many important issues remain unsolved in such complex systems, and the mixture systems need to be explored further
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