TThe shape transformation of polymeric nanostructures attracts much attention of scientists, which can change their rheological, optical and physiological properties, facilitating the exploitation of their potentials in diverse applications. Particularly, the stimuli-responsive transition of nanostructures from amorphous to crystalline state is of high interest in polymer science, but is still challenging. Herein, we demonstrate the transformation of amorphous nanobowls to crystalline ellipsoids triggered by UV induced trans-cis isomerization, using an azobenzene-containing amphiphilic homopolymer (PAzoAA) as building block. The amide bond and azobenzene pendants are introduced to the side chain of PAzoAA to afford hydrogen bonding and π-π interaction, which promotes the formation of nanobowls, which are asymmetric hollow structures with a large opening on the surface, showing advantages such as efficiently encapsulation, delivery and releasing of large sized cargoes on demand comparing with solid nanoparticles or closed hollow structures. Upon exposed to UV irradiation, the trans-cis isomerization of azobenzene pendants occurs, leading to the increase of hydrophilicity of PAzoAA and destruction of π-π interaction, further resulting in the disassembly of the nanobowls. Then the PAzoAA re-assembles to form crystalline ellipsoids instead of amorphous nanostructures when recovered at 70 °C without UV light. We further confirm that the high incubation temperature after UV irradiation is critical for the cis-trans transformation and the high mobility of the polymer chains to facilitate the regular rearrangement of azobenzene pendants. Overall, we propose a facile method to achieve the transformation of amorphous nanobowls to crystalline ellipsoids, which may bring new insight into preparation of crystalline nanoparticles using amorphous precursors.

The self-assembly of PAzoAA to form nanobowls and the <i>trans-cis</i> isomerization induced transformation of amorphous nanobowls to crystalline ellipsoids.

The self-assembly of PAzoAA to form nanobowls and the trans-cis isomerization induced transformation of amorphous nanobowls to crystalline ellipsoids.

Xiaoyan Zhou

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