Direct coating of copper nanoparticles on flexible substrates from copper precursors using underwater plasma and their EMI performance

Highlights

• Underwater plasma system for the direct coating of metal nanoparticles.

• One-pot process for synthesis and coating of nanoparticles using an underwater plasma.

• Rapid and cost-effective process to fabricate EMI shielding textile.

Abstract

The metal coated textiles and polymer films have become increasingly important in view of electromagnetic interference (EMI) shielding. In this study, we propose a simple underwater plasma system for direct coating of copper nanoparticles on textiles and polymer films to intercept electromagnetic wave. The proposed system can synthesize copper nanoparticles and coat it on substrate at once. We analyzed the characteristics of coating layer in order to optimize coating fabrication. When the copper nanoparticles were coated using optimized condition, the thickness of coating layer is about 1 μm and sheet resistance is about 95.44 mΩ/sq. The improved conductivity of polyimide film and nonwoven fabric significantly contributed to effective shielding of electromagnetic interference measured at 38.83 and 82.31 dB in frequency from 1 to 10 GHz.

Introduction

In recent years, serious electromagnetic interference (EMI) pollution has been documented from the rapidly expanding field of communications and associated devices, such as mobile telephones, local area network systems and radar systems [1], [2]. The EMI shielding technologies have been considered extensively in the electrical and electronic industries owing to the increasing concern about health issues caused by the human exposure to EMI waves [3], [4], [5], [6]. Textiles and polymer films have been considered as EMI shielding applications owing to their desirable properties in terms of flexibility, low mass and low cost.

Textiles and polymer films are intrinsically classified as non-EMI shielding materials. However, they can be successfully converted to EMI shielding materials following raw materials changes, the adoption of new production processes, or the use of process adaptions that make them electrically conductive [7]. Some of methods used to obtain conductive fabrics include the use of metallic fibers and yarns, such as stainless steel, aluminum or copper. However, these types of yarns tend to have non-optimal characteristics such as low flexibility, heavy weight, and increased stiffness. To overcome these problems, many researchers have developed metal coating processes, or other processes to produce conductive textiles or films with the use of conductive fillers or metal deposition process [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. These techniques are not only time-consuming and complex but also require the utilization and know-how owing to using of vacuum process or entire textile fabrication processes such as melt or wet spinning.

In recent years, the metal nanoparticles are of interest owing to their light weight, ease of processing and tunable conductivities as compared to other bulk materials such as metal plate [26], [27], [28], [29], [30], [31]. Silver, gold, and copper nanoparticles are excellent for reflection of electromagnetic waves, owing to their increased conductivities [32]. However, silver and gold nanoparticles are expensive because of the prices of precursors, while copper easily lose its conductivity by surface oxidation. Because of these problems, some groups developed the methods to synthesize copper nanoparticles without surface oxidation [33], [34], [35], [36], [37], [38], [39], [40]. These methods also have numerous disadvantages such as long processing times, use of capping agents to inhibit the oxidation, and low production rates.

In this study, we suggested the use of novel processes to directly coat Cu-NPs on the surface of polymer films with the use of using underwater plasma developed in our previous study [41]. These processes can synthesize NPs and coat them on the substrate at once. These technologies have the advantages of simplicity, fast processing times, and high throughput. We evaluated the characteristics of the coated layers to optimize the NPs coating process based on condition of the process, and measured the electromagnetic interference shielding efficiency of the films which were coated with the NPs.