Longzhen Qiu

Controlled synthesis of magnesium hydroxide nanoparticles with different morphological structures and related properties in flame retardant ethylene?vinyl acetate blends

Magnesium hydroxide nanoparticles with different morphological structures of needle-, lamellar- and rod-like nanocrystals have been synthesized by solution precipitation reactions of alkaline with magnesium chloride in the presence of complex dispersants and characterized in terms of morphology, particle size, crystal habits and thermal behaviour by transmission electron microscopy, x-ray diffraction and thermogravimetric analysis. The sizes and morphologies of magnesium hydroxide nanocrystals can be controlled mainly by the reaction conditions of temperature, alkaline-injection rate and the concentrations of reactants. The data show that the needle-like morphology is of size 10 × 100 nm2, the lamellar shape 50 nm in diameter and estimated 10 nm in thickness, and the rod-like nanoparticles 4 µm in length and 95 nm in diameter, respectively. All three kinds of nanoparticles are of hexagonal structures. The needle- and lamellar-like nanoparticles can be obtained by the reactions of alkaline injected into magnesium chloride solution at about 2 and 20 °C, respectively, while the rod-like nanoparticles can be prepared by a slower alkaline-injection rate and lower aqueous ammonia concentration at about 10 °C. The results obtained from the ethylene–vinyl acetate nanocomposites blended with the lamellar-like nanoparticles show that magnesium hydroxide nanocrystals possess higher flame retardant efficiency and mechanical reinforcing effect by comparison with common micrometre grade magnesium hydroxide particles.

Tailoring Structure and Field-Effect Characteristics of Ultrathin Conjugated Polymer Films via Phase Separation

A phase-separation method has been developed to control the semiconductor thickness and molecular arrangement via the semiconducting/insulating polymer blend system. The thickness of the poly(3-hexylthiophene) film has been regulated from 10.5 ± 1.4 nm down to 1.9 ± 0.8 nm with a favorable self-assembly degree and the mobility ranging from 0.21 to 0.03 cm2 V-1 s-1. The ultrathin films show high bias stability and weak decay after 24 days with a bottom-gate configuration. Benefited from a good molecular order, the films have low activation energy and a 2D charge transport profile in semiconductor layers. Moreover, this blending process can be used as a general strategy of thickness control in flexible low-voltage devices and donor-acceptor-conjugated polymers.

One-step fabrication of high performance organic field-effect transistors from semiconductor/dielectric blends

Vertical phase separation of organic semiconductor/dielectric polymer blends has been used in field-effect transistors (FETs) to fabricate low-voltage devices, improve environmental stability, and reduce semiconductor cost. However, all structures reported in previous studies are dielectric-up and semiconductor-bottom structures, and it is difficult to combine multi-advantages in one system because special materials and methods are used in each case. Here, we first fabricated a semiconductor-top and dielectric-bottom bilayer structure by surface-induced vertical phase separation of conjugated molecules and insulating polymer blends. The use of these bilayered blends as active layer in FETs leads to an improvement of the device performance with a drastic reduction of semiconductor content because insulating polymer layer can act as modifier at the semiconductor/dielectric interface. Moreover, because the insulting polymer layer can be used as dielectric layer without any other dielectrics, the blended films can be used to fabricate high-performance, lowsemiconductor-content, and low-voltage FETs in a one-step process.

Bar-Coated Ultrathin Semiconductors from Polymer Blend for One-Step Organic Field-Effect Transistors

One-step deposition of bi-functional semiconductor-dielectric layers for organic field-effect transistors (OFETs) is an effective way to simplify the device fabrication. However, the proposed method has rarely been reported in large-area flexible organic electronics. Herein, we demonstrate wafer-scale OFETs by bar coating the semiconducting and insulating polymer blend solution in one-step. The semiconducting polymer poly(3-hexylthiophene) (P3HT) segregates on top of the blend film, whereas dielectric polymethyl methacrylate (PMMA) acts as the bottom layer, which is achieved by a vertical phase separation structure. The morphology of blend film can be controlled by varying the concentration of P3HT and PMMA solutions. The wafer-scale one-step OFETs, with a continuous ultrathin P3HT film of 2.7 nm, exhibit high electrical reproducibility and uniformity. The one-step OFETs extend to substrate-free arrays that can be attached everywhere on varying substrates. In addition, because of the well-ordered molecular arrangement, the moderate charge transport pathway is formed, which resulted in stable OFETs under various organic solvent vapors and lights of different wavelengths. The results demonstrate that the one-step OFETs have promising potential in the field of large-area organic wearable electronics.

44.4: Invited Paper: Semiconducting Nanofibers Embedded in Insulating Polymer for Organic Thin-Film Transistors

We have Semiconducting nanofibers embedded in insulating polymer allow a reduction of the semiconductor content to as low as 3 wt % without considerable degradation of the field-effect electronic properties and thus are desirable for achieving excellent charge transport properties in low-cost, large-area, flexible organic thin-film transistors.