Application of a Coupling Agent to Improve the Dielectric Properties of Polymer-Based Nanocomposites

Summary

Here, we demonstrate a simple and low-cost solution-casting process to improve the compatibility between the filler and the matrix of polymer-based nanocomposites using surface modified BaTiO₃ fillers, which can effectively enhance the energy density of the composites.

Abstract

In this work, an easy, low-cost, and widely applicable method was developed to improve the compatibility between the ceramic fillers and the polymer matrix by adding 3-aminopropyltriethoxysilane (KH550) as a coupling agent during the fabrication process of BaTiO₃-P(VDF-CTFE) nanocomposites through solution casting. Results show that the use of KH550 can modify the surface of ceramic nanofillers; therefore, good wettability on the ceramic-polymer interface was achieved, and the enhanced energy storage performances were obtained by a suitable amount of the coupling agent. This method can be used to prepare flexible composites, which is highly desirable for the production of high-performance film capacitors. If an excessive amount of coupling agent is used in the process, the non-attached coupling agent can participate in complex reactions, which leads to a decrease in dielectric constant and an increase in dielectric loss.

Introduction

The dielectrics applied in electrical energy storage devices are mainly characterized using two important parameters: the dielectric constant (ε_r) and the breakdown strength (E_b)^1,2,3. In general, organic materials such as polypropylene (PP) exhibit a high E_b (~10² MV/m) and a low ε_r (mostly <5)^4,5,6 while inorganic materials, especially ferroelectrics such as BaTiO₃, e....

Protocol

1. Surface modification of BT fillers

1. Prepare 20 mL of KH550 solution (1 wt% KH550 in 95 wt% ethanol-water solvent) and ultrasonicate for 15 min.
2. Weigh BT nanoparticles (i.e., the filler) and KH550, respectively, so that fillers can be coated with 1, 2, 3, 4, 5 wt% of the coupling agent. Treat 1 g of BT nanoparticles in 1.057, 2.114, 3.171, 4.228, and 5.285 mL of KH550 solution by 30 min ultrasonication.
3. Evaporate the water-ethanol solvent from the mixture at 80 °C for 5 h and then at 120 °C for 12 h in a vacuum oven.
4. Use the dry BT nanoparticles as the surface modified fillers to prepare BT-VC91 nanocomposites.
....

Results

The free-standing nanocomposite films with different contents of fillers were successfully fabricated as described in the protocol, and were labeled as xBT-VC91, where x is the volume percentage of BT in the composites. The effect of KH550 (coupling agent) on the morphology and microstructure of these BT-VC91 films was studied by SEM and shown in Figure 1. The SEM images of 30BT-VC91 nanocomposites with 1 and 5 wt% coupling agent are shown in Figure 1a and

Discussion

As discussed above, the method developed by this work could successfully improve the energy-storage performance of ceramic-polymer nanocomposites. To optimize the effect of such method, it is critical to control the amount of coupling agent used in ceramic-surface modification. For ceramic nanoparticles with a diameter of ~200 nm, it was experimentally determined that 2 wt% of KH550 could lead to a maximal energy density. For other composite systems, this conclusion may be used approximately when the fillers with the dia.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3-Aminopropyltriethoxysilane (KH550)	Sigma-Aldrich	440140	Liquid, Assay: 99%
95 wt.% ethanol-water	Sigma-Aldrich	459836	Liquid, Assay: 99.5%
BaTiO3 nanoparticles	US Research Nanomaterials	US3830	In a diameter of about 200 nm
Ferroelectric tester	Radiant	Precision-LC100
Glass substrates	Citoglas	16397	75 x 25 mm
Gold coater	Pelco	SC-6
High voltage supplier	Trek	610D	10 kV
Impedance analyzer	Keysight	4294A
N, N dimethylformamide	Fisher Scientific	GEN002007	Liquid
P(VDF-CTFE) 91/9 mol.% copolymer
Scanning Electron Microscopy (SEM)	JEOL	JSM-7000F
Vacuum oven	Heefei Kejing Materials Technology Co, Ltd	DZF-6020