Tailored Self-Assembled Ferroelectric Polymer Nanostructures\nwith Tunable Response

Abstract

A facile ferroelectric\nnanostructures preparation method is developed\nbased on the self-assembly of poly­(2-vinylpyridine)-<i>b</i>-poly­(vinylidene fluoride-<i>co</i>-trifluoroethylene)-<i>b</i>-poly­(2-vinylpyridine) triblock copolymers (P2VP-<i>b</i>-P­(VDF-TrFE)-<i>b</i>-P2VP), and the effect of\nmorphological characteristics of the block copolymers on the ferroelectric\nresponse has been investigated for the first time. By simple adjustment\nof the ratio between the blocks, lamellar, cylindrical, and spherical\nmorphologies are obtained in the melt and preserved upon crystallization\nof P­(VDF-TrFE). However, at high P­(VDF-TrFE) content, crystallization\nbecomes dominant and drives the self-assembly of block copolymers.\nThe crystallization study of the block copolymers reveals the preservation\nof the high degree of crystallinity inside the confined nanodomains\nas well as the reduction of the crystalline size and the Curie transition\ntemperature with the confinement level. Only a small difference in\nthe coercive field and the shape of the hysteresis loop is observed\nfor block copolymers with a lamellar morphology produced\neither by crystallization-driven self-assembly or by confinement inside\npreformed lamellar domains. In contrast, delayed spontaneous polarization\nor the absence of dipole switching is demonstrated for the confinement\nof ferroelectric crystals inside both isolated cylindrical and spherical\ndomains, exemplifying the influence of dimensionality on the critical\nsize for ferroelectric order.