Crystal phases, structure, and orientation in isotactic polypropylene after isothermal crystallization under oscillatory shear as a function of nucleation agent

High-temperature resistant polypropylene films enhanced by atomic layer deposition

Last two decades has witnessed various technical programs towards the development of new dielectric films for high temperature and high energy density capacitor technology. Yet, the organic polypropylene film still holds its top position for film capacitors required for electric and electronic power applications such as power grid, hybrid electric vehicles, oil and gas exploration, and aviation. However, its low temperature stability determined by its structural nature limits its further adoption for more rising markets. This work thus developed a creative method (ultrathin coating of inorganic compound using atomic layer deposition) to increase the high temperature stability and the dielectric strength of such a strategically important polymer film from below 105 °C to above 140 °C. Several techniques also confirmed the effective minimization of the dimensional change and crystallinity loss at higher temperatures, i.e., Thermomechanical analysis, Dynamic mechanical analysis, Dynamic Scanning calorimetry, x-ray diffraction and electron microscopy techniques. This breakthrough discovery adds a huge value to the commercial PP films and relevant capacitor industry and will extend the operation of high-performance PP film capacitors to various high standard applications.

Toward Subtle Manipulation of Fine Dendritic β-Nucleating Agent in Polypropylene

Dendritic β-nucleating agent (β-NA) can readily manipulate the formation of dendritic β-crystal with a unique toughening effect on polypropylene (PP) to drastically enhance the ductility. However, by the current method, the geometric size is too large to fully perform the nucleating efficiency. In this study, by comparatively investigating the effect of molecular weight of PP and diffusion of β-NAs in a PP melt, we proposed a novel carrier strategy that selective enrichment of β-NAs in a PP carrier was followed by directed migration into polymer matrix. Accordingly, the growth of NAs was controlled by the release from the PP carrier, which decreased the available amount of β-NAs during the growth stage. In this case, the viscosity difference between PP carrier and matrix determined the interfacial movement of β-NAs. When the PP carrier and matrix had same molecular weight, the diffusion and release became favorable to facilitate the formation of the dense and fine dendritic aggregates. As a result, the relative content of β-crystals reached 92%, with a drastic increase of ∼82% in the optimal condition compared to the directed compounded PP/β-NAs sample. This study can open a new avenue to tailor the topologies of β-NAs and the ensuing β-crystals for high-performance PP products.

1,2,3,4-Bis(p-methylbenzylidene sorbitol) accelerates crystallization and improves hole mobility of poly(3-hexylthiophene)

The addition of 1,2,3,4-bis(p-methylbenzylidene sorbitol) (MDBS) does not change the nucleation mechanism or the crystal form of poly(3-hexylthiophene) (P3HT), but its presence increases the crystallization temperature (T c) of P3HT, decreases the crystallization half-time (t 1/2) and accelerates P3HT crystallization, which indicates that MDBS is an effective nucleating agent for P3HT. An acceleration of P3HT crystallization by the addition of MDBS decreases the crystalline size and crystallinity of P3HT, and enhances the connectivity between ordered regions of P3HT, leading to the hole mobility rising from 1.99 × 10(-6) to 7.57 × 10(-5) cm(2) V(-1)s(-1) in P3HT:PCBM blend based hole-only devices with sandwich configurations. Our results suggest that accelerating P3HT crystallization by adding a nucleating agent might be an important factor to improve the hole mobility and balance the electron and hole mobility in a photovoltaic blend.