Novel Application of Diffuse Coplanar Surface Barrier Discharge: Fast, Efficient and Controlled Surface Functionalization
Authors: Skácelová Dana , Krumpolec Richard , Sihelník Slavomír , Medvecká Veronika , Černák Mirko , Kováčik Dušan 
Published: August 2024

Plasma chemistry is currently an interesting approach to surface modification of materials. In general plasma treatment is a fast process, affecting only the units of nanometers of the surface layer without altering the bulk properties. and has many potential benefits such as minimal waste and control of surface functionality. It represents a dry and environmentally friendly process that can achieve comparable results to wet chemical treatment. The research and development of plasma sources, mainly operating at atmospheric pressure, has been the main activity of the centre CEPLANT, Brno, Czech Republic for several decades. Our development is generally aimed at fast, efficient, and low-cost plasma treatments, easily implementable in industry, and flexibly responds to industrial requirements and current trends.

One of our most versatile plasma source, the so-called Diffuse Coplanar Surface Barrier Discharge (DCSBD) has been developed for in-line surface modification of various materials, primarily for fabric materials. DCSBD produces a 0.3 mm thin layer of non-equilibrium, cold macroscopically diffuse plasma at atmospheric pressure (Fig. 1) in any working gas, including oxygen, hydrogen, or even water vapors. Due to its strongly non-equilibrium nature, operation at atmospheric pressure, and low temperatures, the DCSBD represents a unique plasma source suitable for surface modification of low-cost and temperature-sensitive materials [1-4].

Unique results have been achieved in research on the practical application of flexible conductive layers on glass, with a focus on the deposition of transparent organic polymer coatings on ultra-thin flexible glass (UTFG). We have developed and optimized efficient and fast dry non-contact cleaning and activation of fragile and lightweight conductive glasses using DCSBD. The high-speed plasma treatment corresponding to the exposure times in the order of units of seconds leads to a synergistic balance between the efficient removal of impurities (carbohydrates) adsorbed on the UTFG surface and the formation of oxygen-based functional groups. Subsequent PEDOT:PSS-based coatings sprayed on plasma-treated UTFG surfaces achieve significantly higher electrical conductivity compared to the standard liquid-purified samples. This method combined with the unique properties of UTFG provides prospective results applicable in microelectronics, and optoelectronic devices like sensors or displays.

In the field of composite materials research, we have discovered that plasma treatment of reinforcing fibers leads to improvement of the mechanical properties of laminated fiber-reinforced polymer (FRP) composites. Efficient functionalization of various commonly used reinforcement fibers (flax, aramid and glass) in atmospheric low-temperature DCSBD increases the interfacial adhesion at the fiber-matrix interface, which has a provable positive effect on the resulting mechanical properties.

DCSBD plasma can also be utilized for the initiation of reducing chemical reactions. We have developed a simple and fast chemical-free fabrication method of 2D and 3D reduced graphene oxide (rGO) structures using an electrical plasma-triggered reduction & exfoliation of 3D porous graphene oxide (GO) aerogel-like materials [4] and also 2D GO paper-like films starting at temperatures not higher than 100 oC [5]. The plasma triggered the self-propagating reduction & exfoliation fast modification of GO into rGO, while the rGO structures retained their original shape without abrupt disintegration. We observed an approximately 105 fold decrease of the rGO paper resistivity compared to the unmodified GO paper. This novel method opens new opportunities for the production of conductive rGO and rGO-based composites for modern industrial applications.

Innovative results were achieved in the fabrication of ZnO nanofibers by a novel calcination approach assisted by DCSBD. Exposition of the polyvinyl pyrrolidone/zinc acetate fibers to DCSBD before the thermal processing leads to the gentle low-temperature removal of organic material. Plasma pre-treated nanofibers are characterized by a smaller diameter and retain a defined fibrous structure during heat treatment. Moreover, the ZnO nanofibers prepared by a combination of plasma and heat treatment exhibited considerably higher photodegradation activity increasing with decreasing calcination temperature [6]. The low-temperature and high oxidation potential of plasma makes plasma-assisted calcination of the inorganic nanofibers an attractive alternative to conventional thermal annealing with potential application in optoelectronics or biosensors.

The mentioned applications are only a small fragment of available cases of utilization of the DCSBD, which is now commonly established and applied in the field of surface modification of various materials (glass, metals, non-woven fabrics, polymers, paper, nanofibres) and biomaterials (seeds, grains, wood, natural leather).

[1] M. Černák et al., Plasma Physics and Controlled Fusion 53 (2011) 1-8

[2] R. Talviste et al., Surface and Interface 16 (2019) 2468-0230

[3] T. Morávek et al., Open Chemistry 13 (2015) 236-244

[4] R. Krumpolec et al., Flatchem 35 (2022)

[5] F. Zelenák , Carbon N. Y. 215 (2023) 118436

[6] V. Medvecká et al., Applied Surface Science, 581 (2022) 152384

Figure 1