Self-assembly of homopolymers through strong dipole-dipole interaction in their aqueous solutions

- Mechanism of homopolymers to form self-assembled microspheres in aqueous solutions is studied.
- The critical importance of dipole-dipole interaction for the self-assembly is revealed.
- The dipolar groups play the role of attractive “stickers” to cause the aggregation.
- The self-assembling intermediates show physical gelation like microgel.
- The final assemblies are formed through collapse of the swollen aggregates.

This study reveals the critical importance of dipole-dipole interaction for homopolymers to form self-assembled microspheres in solutions. For the polymers with different side-groups, the self-assembly is induced by gradually adding deionized water into their solutions in N, N-dimethylformamide (DMF). Three of the polymers containing side-groups with the strong dipoles form uniform colloidal spheres in the processes. Beyond the critical water content (CWC), the aggregate sizes first increase and then decrease with the increasing water content before forming the final assemblies. In the intermediate states, the aggregates possess a microgel-like structure in the swollen form. On the other hand, no such self-assembling behavior is observed for the other polymer without the dipolar side-groups, which precipitates from the DMF-H2O solution with the increase in the water content. The strong dipolar groups acting as associating groups are necessary to avoid polymer molecules forming dense aggregates and precipitating from the solutions after phase separation.

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