Plasma and Polymers: Recent Progress and Trends

Abstract

Plasma-enhanced synthesis and modification of polymers is a field that continues to expand and become increasingly more sophisticated. The highly reactive processing environments afforded by the inherently dynamic nature of plasma media are often superior to ambient or thermal environments, offering substantial advantages over other processing methods. The fluxes of energy and matter toward the surface enable rapid and efficient processing, whereas the charged nature of plasma-generated particles provides a means for their control. The range of materials that can be treated by plasmas is incredibly broad, spanning pure polymers, polymer-metal, polymer-wood, polymer-nanocarbon composites, and others. In this review, we briefly outline some of the recent examples of the state-of-the-art in the plasma-based polymer treatment and functionalization techniques.

Keywords: plasma; polymer functionalization; polymers.

Figure 6

(a,b) Combination treatment that involves plasma treatment followed by Ag sputtering improved antimicrobial activity of polytetrafluoroethylene (PTFE) nanotextiles against Gram-negative E. coli and Gram-positive S. epidermidis. Plasma treatment was performed at the input power of 3–8 W for up to 240 s, and the Ag sputtering was performed for 80–300 s. The samples were allowed to incubate in the presence of bacterial culture for 2 h, and then cells were left to grow overnight on agar plates. Reproduced from Slepicka et al. (2021) [58] under the conditions of the CC BY license. (c) The non-thermal plasma pin system used to deliver plasma treatment uniformly over larger surface areas. Not seen on the image is a plastic box that was used to cover the system during treatments and optical measurements. The low-density polyethylene (LDPE) samples were placed within the plasma discharge for the duration of the treatment. Shown is the plasma discharge in ambient air. Reproduced from Scally et al. (2018) [60] under conditions of the CC BY license.

Figure 7

(a) Configuration of the dielectric barrier discharge Y-shaped source. Reproduced from Panaitescu et al. (2020) [73] under conditions of the CC BY license. (b) Scheme of the electrode system of the plasma reactor setup used for plasma nano/microtexturing of Teflon samples. The upper electrode is a shower-head type to allow homogeneous feed of the process gas (O₂ in this case). Samples are placed on the bottom electrode, which is radio-frequency (RF) powered. Reproduced from Mundo et al. (2017) [74] under conditions of the CC BY license. (c) Permeability of Torlon and Torlon/DES-5 composites for He, N₂, and O₂ at 30 °C. Reproduced from Pulyalina et al. (2021) [75] under conditions of the CC BY license. (d) Schematic representation of the two main steps needed for the design of an amphiphilic poly(ether urethane) exposing a tunable amount of carboxylic groups: (I) polyurethane synthesis; (II) powder plasma treatment. (e) Schematic representation of the plasma treatment process: (I) etching phase in the presence of Ar gas to create free radicals on powder surface and (II) grafting step in the presence of Ar gas and acrylic acid vapors to expose carboxylic groups. Reproduced from Laurano et al. (2019) [80] under conditions of the CC BY license.

Figure 8

(a) Schematic representation of polymer deposition during pulse-on and pulse-off pulsed mode in plasma polymerization. Reproduced from Iqbal et al. (2018) [84] under conditions of the CC BY license. (b) Schematic drawing of the atmospheric pressure plasma jet system used for polymer surface modification, and (c) optical photograph of the plasma jet at various distances of the nozzle from the sample. Reproduced from Vesel et al. (2020) [87] under conditions of the CC BY license.

Figure 1

(a) When the surface of the substrate is exposed to plasma, multiple reactions between reactive molecules and radicals can lead to the formation of a film. In plasma, the ions and radicals are formed and accelerate toward the surface. Once they arrive at the surface of the substrate, the following reactions may take place: (1) adsorption and (2) desorption of reactive molecules; abstraction of H by (3) H radical and (4) other radicals; (5) reactive molecule abstraction by radical; direct chemisorption of (6) reactive molecules, and (7) H onto dangling bond; (8) transfer of adsorbed molecules on hydride sites; (9) chemisorption of adsorbed molecules into dangling bonds; and (10) sputtering of mono-hydride sites by ions. Reproduced Marvi et al. (2017) [29] under conditions of the BY-NC license. Diagram of the plasma treatment equipment: (b) plasma device; (c) mechanism of plasma interaction with the polymer surface. Reproduced from Lu et al. (2019) [30] under conditions of the CC BY license.

Figure 2

Common control mechanisms in plasma-enhanced processing of matter across multiple length scales, from particle nucleation at nanoscale, to growth of objects and arrays at micrometer and millimeter scales, respectively. Reactor geometry, energy source, and external electric and magnetic fields can be tuned to optimize the process toward specific growth and functionalization outcomes. DC refers to a direct current source, arc refers to arc plasma, ICP and CCP denote inductively and capacitively coupled plasmas, respectively, DBD denotes dielectric barrier discharges, ECR refers to electron cyclotron resonance plasma sources, and PIII refers to plasma immersion ion implantation. Reproduced with permission from Baranov et al. (2018) [34].

Figure 3

(a) Schematic of cold atmospheric plasma (CAP) source used for the treatment of the ultra-high-molecular-weight polyethylene (UHMWPE) samples. (b) Tip and base treatment locations of the UHMWPE samples in the plasma plume. (c) Contact angle measurements as a function of the treatment time varied from 1 to 26 min. Reproduced from Turicek et al. (2021) [38] under conditions of the CC BY license.

Figure 4

(a) Exposure of polymer surfaces to plasma species leads to surface texturing, with features spanning micro and nano-scales, and simultaneous introduction of functional groups with an affinity for biomolecules, where the latter could be selectively immobilized via physical and covalent bonding in the absence of the linker. (b) Antibody immobilization on pristine and plasma-treated poly(methyl methacrylate) surfaces: (i) 1-Ethyl-3-(3-(dimethylamino)propyl)carbodiimide/N-hydroxysulfosuccinimide (EDC/sHNS) mediated and (ii) linker-free immobilization of antibodies labelled using Au nanoparticles. The mouse IgG antibodies labelled with two different methods were used. Reproduced from Wieland et al. (2020) [40] under conditions of the CC BY license.

Figure 5

(a) Fibronectin (FN) and collagen secretion by the fibroblasts seeded on PCL-ref and PCL-COOH. Cells were stained by antibody Alexa Fluor 594 (orange) to collagen (magnification 40×) and Alexa Fluor 488 to FN (magnification 20×). (b,c) The influence of scaffold surface on (a) cell proliferation and apoptosis, and (b) cell count for three and seven days of cultivation. The arrows indicate the relationship of the level of cell apoptosis and cell proliferation. Reproduced from Miroshnichenko et al. (2019) [41] under conditions of the CC BY license. (d) Cell adhesion of in vitro cultured mouse ASCs onto various plasma-treated films. (e) Cell proliferation rate of in vitro cultured mouse ASCs on PHB, PHB hydrophobic, PHB hydrophilic, PHBV, PHBV hydrophobic, and PHBV hydrophilic surfaces. (f) Concentrations of VEGF secreted from in vitro cultured mouse ASCs on PHB and PHBV films over a 7-day period. Reproduced from Chang et al. (2018) [42] under conditions of the CC BY license. (g) Morphologies of cells on the surfaces of plates: untreated titanium plate (left) and titanium plate treated with amine plasma (right). Nuclei color is blue. (h) Comparison of the average percentage of new bone formation for each specimen in the animal experiments. Reproduced from Jeong et al. (2019) [43] under conditions of the CC BY license. (i) Bacteria S. epidermidis surface coverage area (percent) formed on POx films deposited at different substrate temperatures. Reproduced from Stahel et al. (2019). [44] under conditions of the CC BY license.

Figure 9

(a,b) Schematic of a low-pressure plasma (LPP) reactor used for the surface treatment of polyethylene wood plastic composite (PE-WPC) and chamber scheme and (b) the direct configuration scheme. (c) Schematic of an atmospheric pressure plasma jet (APPJ) system used for the surface treatment of PE-WPC. (d) The 180° peel strength values for an as-received and plasma-treated PE-WPC/acrylic adhesive joints. An adhesion failure always occurred. Reproduced from Yáñez-Pacios et al. (2018) [90] under conditions of the CC BY license.

Figure 10

(a,b) Plasma device used for the surface treatment of 3D-printed samples on a CNC positioning system (top left image) with a gliding arc plasma jet (a), and sample for testing the bond shear strength (b). Reproduced from Kariž et al. (2018) [91] under conditions of the CC BY license. (c,d) Representation of the crack path in ABS-interleaved hybrid composites (c) with untreated ABS (d) with plasma-treated ABS. Reproduced from Marino et al. (2020) [92] under conditions of the CC BY license.

Figure 11

Possible mechanism of surface group oxidation by plasma treatment: (a) generation of C–O bonds, (b) generation of C=O bonds, (c) generation of O–C=O bonds. Reproduced from Lu et al. (2019) [30] under conditions of the CC BY license.

Figure 12

(a) Adhesive shear strength of pristine (grey) and plasma-treated (red) polymer/polymer and polymer/steel joints using various adhesives for PA6 (a) and POM-C (b). Reproduced from Károly et al. (2018) [93] under conditions of the CC BY license.

Figure 13

(a) Experimental setup used for PAVTD of PLA-like coatings and (b) chemical structure of conventional PLA with the assignment of C, O, and H that corresponds to different spectral peaks detectable by XP and NMR, respectively. Reproduced from Krtouš et al. (2021) [94] under conditions of the CC BY license.

Figure 14

Schematic representation of the deposition process in DC and RF plasma jet. Films with lower fraction of carbon were fabricated using RF plasma, with the outcome related to the difference in the injection point of the source material. Reproduced from Kuchakova et al. (2020) [95] under conditions of the CC BY license.