Pulsed Plasma Polymerization Research Articles

Fluorocarbon Plasma-Polymerized Layer Increases the Release Time of Silver Ions and the Antibacterial Activity of Silver-Based Coatings.

Silver-based antibacterial coatings limit the spread of hospital-acquired infections. Indeed, the use of silver and silver oxide nanoparticles (Ag and AgO NPs) incorporated in amorphous hydrogenated carbon (a-C:H) as a matrix demonstrates a promising approach to reduce microbial contamination on environmental surfaces. However, its success as an antibacterial coating hinges on the control of Ag+ release. In this sense, if a continuous release is required, an additional barrier is needed to extend the release time of Ag+. Thus, this research investigated the use of a plasma fluoropolymer (CFx) as an additional top layer to elongate Ag+ release and increase the antibacterial activity due to its high hydrophobic nature. Herein, a porous CFx film was deposited on a-C:H containing Ag and AgO NPs using pulsed afterglow low pressure plasma polymerization. The chemical composition, surface wettability and morphology, release profile, and antibacterial activity were analyzed. Overall, the combination of a-C:H:Ag (12.1 at. % of Ag) and CFx film (120.0°, F/C = 0.8) successfully inactivated 88% of E. coli and delayed biofilm formation after 12 h. Thus, using a hybrid approach composed of Ag NPs and a hydrophobic polymeric layer, it was possible to increase the overall antibacterial activity of the coating.

Comparison of continuous wave and pulsed mode plasma polymerization of glycidol for storage‐stable coatings for biomolecule immobilization

AbstractPlasma polymers from glycidol vapors are of interest for direct covalent grafting of molecules bearing amine or thiol groups. The question of whether pulsed plasma operation might lead to a higher surface density of epoxide groups and a higher density of grafted molecules is studied using the antifungal drug caspofungin. X‐ray photoelectron spectroscopy and Time of flight‐secondary ions mass spectrometry analysis followed by caspofungin grafting revealed that both continuous wave and pulsed plasmas led to surface epoxides but with higher densities upon pulsing. Investigations into stability suggested that glycidol plasma polymer coatings were still able to immobilize caspofungin after 2 years of storage, making them suitable for applications where grafting of molecules needs to be done immediately before usage of a device.

Confined Crystallization of Thin Plasma-Polymerized Nanocomposite Films with Maleic Anhydride and Cellulose Nanocrystals under Hydrolysis.

The creation of novel surface morphologies through thin-film patterning is important from a scientific and technological viewpoint in order to control specific surface properties. The pulsed-plasma polymerization of thin nanocomposite films, including maleic anhydride (MA) and cellulose nanocrystals (CNC), may result in different metastable film morphologies that are difficult to control. Alternatively, the transformation of deposited plasma films into crystalline structures introduces unique and more stable morphologies. In this study, the structural rearrangements of plasma-polymerized (MA+CNC) nanocomposite films after controlled hydrolysis in a humid atmosphere were studied, including effects of plasma conditions (low duty cycle, variable power) and monomer composition (ratio MA/CNC) on hydrolysis stability. The progressive growth of crystalline structures with fractal dendrites was observed in confined thin films of 30 to 50 nm. The structures particularly formed on hydrophilic substrates and were not observed before on the more hydrophobic substrates, as they exist as a result of water penetration and interactions at the film/substrate interface. Furthermore, the nucleating effect and local pinning of the crystallites to the substrate near CNC positions enhanced the film stability. The chemical structures after hydrolysis were further examined through XPS, indicating esterification between the MA carboxylic acid groups and CNC surface. The hydrolysis kinetics were quantified from the conversion of anhydride groups into carboxylic moieties by FTIR analysis, indicating enhanced hydrolytic stability of p(MA+CNC) nanocomposite films relative to the pure p(MA) films.

Pulsed plasma polymerisation of carvone: characterisations and antibacterial properties

The production of suitable coatings with excellent antibacterial performance has now become a viable technique for enhancing the functional qualities of various biomedical materials. Here, pulsed plasma polymerisation was used to produce an antibacterial coating from the carvone oil of the spearmint plant. The coating films have adjustable chemical and physical properties based on the deposition parameter – that is, duty cycle (DC). The static water contact angle (WCA) values of pulsed wave (PW) plasma-polymerised carvone (ppCar) increase with the increase in DC. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the molecular structure of carvone is less fragmented, retaining moieties associated with C–O and C=O when the DC is reduced. These C–O and C=O moieties likely reduced the measured static WCA. This surface chemical composition with predominantly C–O and C=O also showed a stronger bactericidal effect, based on the biofilm assay with bacteria (Escherichia coli and Staphylococcus aureus), compared with those coatings with C–C and C–H produced at a higher DC. As shown by the atomic force microscopy images, a lower DC resulted in smoother and more homogeneous coatings than those produced with a higher DC, while field emission scanning electron microscopy images show that when E. coli and S. aureus membranes were attached to PW ppCar, they ruptured and distorted with a pore created and that these distortions and ruptures increased as the DC was reduced.

Femtosecond laser surface roughening and pulsed plasma polymerization duplex treatment on medical-grade stainless steel substrates for orthodontic purpose

This study developed a surface modification technique to obtain nearly superamphiphobic films on AISI 304 stainless steel substrates, which are usually made into dental appliances in orthodontics for malocclusion. Direct fabrication of micro- and nanoscale roughened surfaces on stainless steel substrates were treated using femtosecond laser (FL) processing. Subsequently, pulsed plasma polymerization (P3) was adopted using hexamethyldisiloxane (C6H18OSi2) and octafluorocyclobutane (C4F8) as the precursors to deposit siloxane and fluorocarbon stacking films. The surface characteristics of the deposited films were examined, and in vitro cytotoxicity and antimicrobial tests were performed. Experimental results showed that the surfaces treated by FL and P3 processes exhibited nearly superamphiphobicity with water apparent contact angle (CA) 160°, advancing CA 161°, receding CA160°, contact angle hysteresis (CAH) 1°; sunflower oil apparent contact angle 146°, advancing CA 141°, receding CA137°, CAH 4°; and hexadecane oil apparent contact angle 124°, advancing CA 118°, receding CA113°, contact angle hysteresis CAH 5°, respectively. The nearly superamphiphobicity are attributed to the synergistic effects of pre-roughening by the FL process and post-flourinating with siloxane and fluorocarbon coating by the P3 process, which were consistent with the results of scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared analyses. In addition, the steel wool abrasion test exhibited the film's surface wear resistance, and in vitro tests revealed the film's non-cytotoxicity and effective inhibition of bacterial growth. Thus, the nearly superamphiphobic coating may be beneficial for applications in orthodontics.

Thin films deposition versus nanoparticles formation: How can the desired polymer coating be obtained?

AbstractThe properties of the final product resulting from plasma polymerization strongly depend on the operating conditions and they impact the final application of the plasma polymer coating. Low‐pressure pulsed plasma polymerization of maleic anhydride was investigated at two different positions in relation to the glow discharge in a 1‐m‐long tubular reactor. Interestingly, competition was observed in the deposition of maleic anhydride plasma polymer in the form of a smooth thin film versus that in the form of nanoparticles. The possibility of a spatiotemporal control of plasma polymerization enabled the deposition of a plasma coating with tunable morphological properties depending on the sample position from the glow discharge and on the plasma pulse parameters (on‐timeandoff‐time).

Plasma-assisted fibrillation and surface-modification of microfibrillar cellulose

The combination of microcrystalline cellulose (MCC) with maleic anhydride (MA) allowed for in-situ fibrillation and surface modification during pulsed plasma polymerization. Under optimized plasma parameters, the microfibrillated cellulose (MFC) morphology could be tuned according to the positioning in the reactor from small and short fibrils towards more elongated and crystallite structures in relation to the complex interactions between activated species. The chemical surface esterification was verified and resulted in good dispersion and higher water contact angle of the fibrils. The proposed route is an attractive ‘green’ and low-energy alternative for traditional mechanical processing and modification of nanocelluloses.

Unique combination of spatial and temporal control of maleic anhydride plasma polymerization

AbstractThe chemical properties of plasma polymers strongly depend on the operating conditions of plasma polymerization and impact their final application. Low‐pressure pulsed plasma polymerization of maleic anhydride was investigated at different positions from the glow discharge in a unique 1‐m‐long reactor. Based on a macroscopic approach, the growth kinetics of maleic anhydride plasma polymerization was investigated, leading to the identification of three growth regimes. The calculation of apparent activation energies associated with each regime and each position and the chemical characterization of polymer films by X‐ray photoelectron spectroscopy and attenuated total reflection–Fourier‐transform infrared as well as optical emission spectroscopy analyses of plasma species formed during deposition strongly indicate a combined spatial and temporal influence on the plasma polymerization kinetics.

Characterization of functionalized coatings prepared from pulsed plasma polymerization

Material assembly based on elastomer part and metallic substrate has been widely used in many industrial sectors. However, the adhesion between the two materials requests specific processes and adhesives. Plasma technology is an interesting way to prepare the assembly since the plasma polymer layers used for the adhesive joint can bear different reactive chemical functions toward the elastomer. Three different plasma coatings are synthesized from acetylene, acrylic acid, and maleic anhydride plasma because of their respective chemical functions able to open the carbon-carbon double bond of the elastomer (rubber, fluoroelastomer). For such a purpose, fine-tuning of plasma parameters was essential to preserve the precursor chemistry and to avoid any degradation. Pulsed plasma discharge was selected, plasma parameters defined thanks to the design of experiment. The different plasma polymers were characterized by FTIR, XPS and NEXAFS spectroscopies and surface energy measurement.

Direct current gas–liquid phase pulsed plasma polymerization of polypyrrole under atmospheric pressure

AbstractIn this study, an atmospheric‐pressure nanosecond impulse discharge initiated above the pyrrole microemulsion surface is applied to polymerize pyrrole and obtain a polypyrrole film. The films obtained under different number of plasma discharge times and duration of argon gas input time are investigated using a field emission scanning electron microscope. Results show that the roughness and thickness of the polypyrrole film can be tuned by controlling discharge times and the gas feed time. Four‐point sheet resistance measurements of the films reflect that those with a smoother and more complete surface have better electrical conductivity. The films are identified as polypyrrole by Fourier‐transform infrared spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectrometry. Also, N2 is a critical factor in polymerizing polypyrrole and the gas–liquid plasma polymerization mechanism, which has three steps, is discussed.

Molecular dynamics simulation of amine groups formation during plasma processing of polystyrene surfaces

Plasma treatment and plasma polymerization processes aiming to form amine groups on polystyrene surfaces were studied in-silico with molecular dynamics simulations. The simulations were compared with two experiments, (i) plasma treatment in N2/H2 bipolar pulsed discharge and (ii) plasma polymerization in cyclopropylamine/Ar radio frequency (RF) capacitively coupled discharge. To model favorable conditions for the incorporation of primary amine groups, we assumed the plasma treatment as the flux of NH2 radicals and energetic NH3 ions, and the plasma polymerization as the flux of cyclopropylamine molecules and energetic argon ions. It is shown in both the simulation and the experiment that the polystyrene treatment by the bipolar pulsed N2/H2 plasmas with an applied voltage of about ±1 kV formed a nitrogen-rich layer of a thickness of only a few nm. The simulations also showed that, as the NH3 incident energy increases, the ratio of primary amines to the total number of N atoms on the surface decreases. It is because the energetic ion bombardment brakes up N–H bonds of primary amines, which are mostly brought to the surface by NH2 radical adsorption. Our previous experimental work on the CPA plasma polymerization showed that increased RF power invested in the plasma leads to the deposition of films with lower nitrogen content. The MD simulations showed an increase of the nitrogen content with the Ar energy and a limited impact of the energetic bombardment on the retention of primary amines. Thus, the results highlighted the importance of the gas-phase processes on the nitrogen incorporation and primary amines retention in the plasma polymers. However, the higher energy flux towards the growing film clearly decreases amount of hydrogen and increases the polymer cross-linking.

Fabrication of Highly Stable Non-Volatile Memory Device Using Plasma-Polymerisation of Hexamethyldisiloxane with Graphene Quantum Dots

We demonstrated the fabrication of a highly stable non-volatile memory (NVM) device using pulsed radiofrequency (rf) plasma polymerization and a simple solution route. The two-terminal NVM devices were fabricated based on a metal-insulator-metal (MIM) structure consisting of graphene quantum dots (GQDs) embedded in hexamethyldisiloxane (HMDSO) dielectric layers. GQDs, the charge trapping layer, and the top contacts were formed by spin coating and spray coating methods. Whereas, the dielectric layers were deposited using pulsed rf plasma polymerization as it is a no thermal stressed induced method to deposit the insulator layers and does not disturb the deposited charge trapping nanoparticles. The current-voltage (I-V) curves showed highly reproducible bistable current behavior with the presence of a hysteresis window when measured at room temperature. The fabricated NVM memory devices were reprogrammable for multiple times with a distinct ON/OFF ratio of 103. Various conduction mechanisms were proposed based on the obtained I-V data.

Pulsed plasma surface functionalized nanosilver for gene delivery.

Lack of suitable surface properties in biomaterials is an acute challenge for their utilization in nucleic acid delivery, since surface plays a vital role in cell adhesion/uptake and immunity. Low pressure cold plasma is a promising technology for functionalization and surface modification of materials, in an effective, environment friendly and economical way. In this investigation we have modified the surface of silver nanoparticles (AgNPs) with chitosan biopolymer, using plasma treatment, to extend their application scope in intracellular DNA delivery. The plasma functionalized; chitosan modified AgNPs (MetaloPolymeric Nanocarriers; MPNCs) possessed superior biocompatibility compared to unmodified AgNPs. Carboxylic groups were incorporated on the surface of nanosilver using 3600 rotating pulsed plasma reactor and acrylic acid vapors were used as precursor gas. Pulsed plasma polymerization process was optimized with respect to working pressure of the system, duty cycle for pulsing, time of treatment and flow rate. Biocompatibility of the plasma functionalized nanosilver was enhanced by coupling it with Chitosan Oligosaccharide (COS), using EDC (1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide) to form amide linkages. The resulting MPNCs showed high cell viability and bio-stability, which was attributed to plasma processing of nanosilver and its association with COS. In vitro cellular studies illustrated significant uptake of nanoplexes. The study suggested the potential of plasma functionalization for manipulating surfaces of metallic nanoparticles to enhance their application in intracellular gene delivery.

Tunable surface chemistry and wettability of octafluorocyclobutane and acrylic acid copolymer combined LDPE substrate by pulsed plasma polymerization

Octafluorocyclobutane and acrylic acid (C4F8-co-AA) are plasma copolymerized onto low-density polyethylene (LDPE) and glass slides under various pulsation periods of radio frequency pulsed plasma. The surface wettability of plasma polymer coating is traditionally considered as a substrate-independent property. The combined effect of ultrathin C4F8-co-AA coatings and LDPE substrate on surface wettability is presented. The high concentration of the carboxylic acid functional groups gives rise to hydrophilicity via lowering duty cycle, and substrate impact gives rise to hydrophobicity for ultrathin coatings. The X-ray photoelectron spectroscopy and coating thickness measurements confirmed that the sudden increase in water contact angle for the lower duty cycle is influenced by the hydrophobic substrate for ultrathin polymer coatings. It is highlighted that the precise control over the surface wettability is attained by tuning the plasma parameters. The substrate-dependent wettability for flat substrate persisted for longer than 8 weeks, which demonstrates wetting stability for ultrathin coatings.

Tuning of the electrochemical properties of transparent fluorine-doped tin oxide electrodes by microwave pulsed-plasma polymerized allylamine

We report here the dry, one-step, and low-temperature modification of FTO surfaces using pulsed plasma polymerization of allylamine (PPAAm). PPAAm/FTO surfaces were characterized by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and contact angles to understand the morphological, structural, and optical properties. FTO were coated with a very thin layer of adherent cross-linked, pinhole-, and additive-free allylamine plasma polymer resistant to hydrolysis and delamination, and characterized by a high density of positively charged amino groups. Electrochemical studies revealed that PPAAm/FTO electrodes show wide range pH stability and reaction rates tuned by the duration of plasma treatment. We show how the modification of plasma treatment duration between 72 s and 288 s affects the chemical structure and thickness of the obtained modification, having a strong influence on the charge transfer kinetics. In particular, XPS revealed the occurrence of the reduction processes under long-term plasma exposure proving the need for monitoring of this key factor. This covalent immobilization of amine compounds on FTO surface using rapid process in microwave pulsed-plasma makes it a promising electrode for future applications in electrochemical biosensors and optoelectronic devices.

Atmospheric Aerosol Assisted Pulsed Plasma Polymerization: An Environmentally Friendly Technique for Tunable Catechol-Bearing Thin Films.

In this work, an atmospheric aerosol assisted pulsed plasma process is reported as an environmentally friendly technique for the preparation of tunable catechol-bearing thin films under solvent and catalyst free conditions. The approach relies on the direct injection of dopamine acrylamide dissolved in 2-hydroxyethylmethacrylate as comonomer into the plasma zone. By adjusting the pulsing of the electrical discharge, the reactive plasma process can be alternatively switch ON (tON) and OFF (tOFF) during different periods of time, thus allowing a facile and fine tuning of the catechol density, morphology and deposition rate of the coating. An optimal tON/tOFF ratio is established, that permits maximizing the catechol content in the deposited film. Finally, a diagram, based on the average energy input into the process, is proposed allowing for easy custom synthesis of layers with specific chemical and physical properties, thus highlighting the utility of the developed dry plasma route.

Interfacial Diels–Alder Reaction between Furan-Functionalized Polymer Coatings and Maleimide-Terminated Poly(ethylene glycol)

Surface functionalization is an interesting way to elaborate new smart materials. In this work, a two-step surface modification, based on pulsed plasma polymerization, was used to design functional...

Control of Interfacial Diels-Alder Reactivity by Tuning the Plasma Polymer Properties.

Functionalizing the surface of a material with a smart plasma polymer coating is an interesting alternative strategy to obtain a thermoresponsive material without changing its formulation. On the basis of a low-pressure plasma polymerization process, the present work first aims to fabricate polymer thin films that react via the well-known thermoreversible Diels-Alder (DA) reaction (diene/dienophile cycloaddition). A two-step surface modification process based on (pulsed) plasma polymerization enables the design of functional coatings that contain furan (diene) groups. The reactivity of these surfaces with maleic anhydride (dienophile) in solution is thoroughly investigated, mainly by studying the kinetics of the DA reaction by advancing contact angle measurements. The determination of rate constants of reactions at various temperatures leads to the quantification of thermodynamic parameters such as the activation energy of the reaction as well as the enthalpy and entropy of activation related to the formation of the transition-state complex involved in the DA reaction. More interestingly, the design of furan-functionalized coatings with various physicochemical properties enables the understanding of the role played by the density of functional groups and the cross-linking rate of the polymer on the interfacial reactivity. Thus, we show in this work how to control the interfacial DA reaction on plasma coatings by tailoring the operating conditions of plasma polymerization.

Carboxyl-Functionalized Nanoparticles Produced by Pulsed Plasma Polymerization of Acrylic Acid.

Carboxyl-enriched and size-selected polymer nanoparticles (NPs) may prove to be very useful in biomedical applications for linker-free binding of biomolecules and their transport to cells. In this study, we report about the synthesis of such NPs by low-pressure low-temperature pulsed plasma polymerization of acrylic acid. Gas aggregation cluster source was adapted to operate plasma with a constant pulse period of 50 μs and with varying duty cycle. The NPs were produced with the size ranging from 31 ± 5 to 93 ± 14 nm and with retention of the carboxyl groups ranging from 4.0 to 12.0 atom %. Two regimes of the NP formation were identified. In the large duty cycle regime, the NP growth was interfered with by positive ion bombardment which resulted in the ion-driven detachment of the carboxyl species and in the formation of carboxyl-deficient NPs. In the small duty cycle regime, the NP growth was accompanied by the radical-driven chain propagation with the attachment of intact monomer molecules. Improved efficacy of the monomer retention resulted in increased concentration of the carboxyl groups.

Fabrication of transparent bistable switching memory device using plasmapolymerized hexamethyldisiloxane layers with embedded graphene quantum dots

We demonstrated the feasibility to fabricate two-terminal non-volatile-memory (NVM) devices using pulsed radio frequency (rf) plasma polymerization and simple solution route. The two-terminal NVM devices were fabricated based on a metal-insulator-metal structure consisting of graphene quantum dots (GQDs) embedded in hexamethyldisiloxane dielectric layers. The charge trapping layer, GQDs and the top contacts were formed by spin coating and spray coating methods. Whereas, the dielectric layers were deposited using pulsed rf plasma polymerization. The current-voltage curves showed a bistable current behavior with the presence of hysteresis window. The fabricated NVM memory devices were reprogrammable when the endurance test was performed and stable up to 1×104s cycles with a distinct ON/OFF ratio of 104. Based on the obtained I-V characteristics, Schottky emission, Poole-Frenkel emission, trapped-charge limited-current and space-charge-limited current were proposed as the dominant conduction mechanisms for the fabricated NVM devices.