Crystallization of Isotactic Polypropylene under the Spatial Confinement Templated by Block Copolymer Microdomains

Pronounced Surface Effects on the Curie Transition Temperature in Nanoconfined P(VDF-TrFE) Crystals

Changes in the Curie transition temperature of nanoconfined poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) copolymers can have a severe impact on the electroactive behavior and the application range of these materials. Therefore, the origin of the change in the Curie transition temperature requires a profound understanding. In this work, block copolymer self-assembly into a spherical morphology proves to be a viable method to effectively confine P(VDF-TrFE) in three dimensions for studying the effect of nanoconfinement on the Curie transition. Using differential scanning calorimetry and wide-angle X-ray scattering, easily accessible experimental techniques, we follow the crystalline phase transitions, showing that confining P(VDF-TrFE) in a nonpolar polystyrene (PS) or poly(4-tert-butoxystyrene) (PtBOS) matrix results in an increase of the Curie transition upon cooling and heating. However, when a more polar matrix is used to nanoconfine P(VDF-TrFE), the Curie transition temperature is drastically reduced due to surface effects.

Electroactive materials with tunable response based on block copolymer self-assembly

Ferroelectric polymers represent one of the key building blocks for the preparation of flexible electronic devices. However, their lack of functionality and ability to simply tune their ferroelectric response significantly diminishes the number of fields in which they can be applied. Here we report an effective way to introduce functionality in the structure of ferroelectric polymers while preserving ferroelectricity and to further tune the ferroelectric response by incorporating functional insulating polymer chains at the chain ends of ferroelectric polymer in the form of block copolymers. The block copolymer self-assembly into lamellar nanodomains allows confined crystallization of the ferroelectric polymer without hindering the crystallinity or chain conformation. The simple adjustment of block polarity leads to a significantly different switching behavior, from ferroelectric to antiferroelectric-like and linear dielectric. Given the simplicity and wide flexibility in designing molecular structure of incorporated blocks, this approach shows the vast potential for application in numerous fields.

Tailored Self-Assembled Ferroelectric Polymer Nanostructures with Tunable Response

A facile ferroelectric nanostructures preparation method is developed based on the self-assembly of poly(2-vinylpyridine)-b-poly(vinylidene fluoride-co-trifluoroethylene)-b-poly(2-vinylpyridine) triblock copolymers (P2VP-b-P(VDF-TrFE)-b-P2VP), and the effect of morphological characteristics of the block copolymers on the ferroelectric response has been investigated for the first time. By simple adjustment of the ratio between the blocks, lamellar, cylindrical, and spherical morphologies are obtained in the melt and preserved upon crystallization of P(VDF-TrFE). However, at high P(VDF-TrFE) content, crystallization becomes dominant and drives the self-assembly of block copolymers. The crystallization study of the block copolymers reveals the preservation of the high degree of crystallinity inside the confined nanodomains as well as the reduction of the crystalline size and the Curie transition temperature with the confinement level. Only a small difference in the coercive field and the shape of the hysteresis loop is observed for block copolymers with a lamellar morphology produced either by crystallization-driven self-assembly or by confinement inside preformed lamellar domains. In contrast, delayed spontaneous polarization or the absence of dipole switching is demonstrated for the confinement of ferroelectric crystals inside both isolated cylindrical and spherical domains, exemplifying the influence of dimensionality on the critical size for ferroelectric order.

Nanoconfinement-Induced β-Phase Formation Inside Poly(vinylidene fluoride)-Based Block Copolymers

The electroactive properties of poly(vinylidene fluoride) (PVDF) are a direct consequence of its crystalline phases. Although poorly understood, nanostructuring PVDF in confined geometries can drastically change its crystallization behavior. Therefore, we synthesized a variety of PVDF-based triblock copolymers to gain a better understanding of the melt crystallization and explore how crystallization is affected by the morphology and chemical nature of the amorphous block. Differential scanning calorimetry, small-/wide-angle X-ray scattering, and transmission electron microscopy gave us excellent insights into the morphology and the corresponding crystalline phases. We find that crystallization of PVDF inside spherical nanodomains occurs via a homogeneous nucleation mechanism leading to a large undercooling and the formation of the thermodynamically favorable ferroelectric β-phase. On the contrary, when confined crystallization occurs inside a lamellar morphology, or in the case of breakout crystallization, a heterogeneous nucleation process leads to the formation of the nonferroelectric α-phase. Furthermore, favorable melt interactions between both blocks induce crystallization into the polar γ-phase at moderate cooling rates.

CuAAC click chemistry: a versatile approach towards PVDF-based block copolymers

Functionalized benzoyl peroxide-initiated polymerization of vinylidene fluoride allows straightforward preparation of PVDF-based block copolymers with an appealing crystallization behavior.

Homogeneous crystal nucleation in polymers

The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 10⁶ K s^-1, allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability. As for other materials, the maximum homogeneous nucleation rate for polymers is located close to the glass transition temperature. In the experiments discussed here, it is shown that polymer nucleation is homogeneous at such temperatures. Homogeneous nucleation in polymers is discussed in the framework of the classical nucleation theory. The majority of our observations are consistent with the theory. The discrepancies may guide further research, particularly experiments to progress theoretical development. Progress in the understanding of homogeneous nucleation is much needed, since most of the modelling approaches dealing with polymer crystallization exclusively consider homogeneous nucleation. This is also the basis for advancing theoretical approaches to the much more complex phenomena governing heterogeneous nucleation.