Plasma Polymer Films Research Articles

Development of mass sensitive sensor platform based on plasma polymerization technique: Quartz tuning fork as transducer

This paper describes a modification process of QTFs’ prongs with stable amine containing bilayer plasma polymer film and an application of quartz tuning fork (QTF) as a transducer for biomedical application. To produce stable amine containing film, first, we created plasma polymer films from hexane precursors. We then subjected those films to a second capping layer of ethylenediamine plasma polymer. The film was characterized by contact angle measurement, atomic force microscopy, and X-ray photoelectron spectroscopy. The effect of the interfacial structure onto stability was also analyzed in air. A model protein, BSA, sensing experiments were examined by measuring the shift in the resonance frequency of QTFs. The performance of the proposed sensor was investigated in terms of quality factor. These findings reveal that amine containing bilayer coated QTFs have the potential to be used in mass sensitive biosensor applications for future.

Stability of oxygen-rich plasma-polymerized coatings in aqueous environment.

In this work, we report on the stability of oxygen-rich plasma-polymerized (pp) films in an aqueous environment. The pp films were deposited via atmospheric-pressure plasma jet treatment of polymerizable organic liquids. The monomers used for the plasma-assisted polymerization were tetrahydrofurfuryl methacrylate, 1,2,4-trivinylcyclohexane, and mixtures thereof. The pp films were deposited at different plasma input powers ranging from 3 to 7 W. The stability of the obtained pp films was studied upon long-time storage in pure water and in buffer solutions of pHs 4, 7, and 10. After 24 h of storage of the pp films in de-ionized water, all of the studied pp films experienced thickness losses along with the formation of various ringlike structures at their surface, whereas Fourier transformed infrared (FT-IR) analysis showed no changes in their chemical composition. The pp films stored in pH 10 were completely delaminated from the substrate surface, while the pp films stored for 24 h in pH 4 showed swelling behavior, partial delamination, and the formation of wrinkles at the coatings' surface. The pp films stored for 24 h in pH 7 experienced minor thickness losses and formation of wrinkles at their surface. FT-IR analysis of the pp films stored in buffer solutions of pH 4 and pH 7 showed a decrease of C=O and an increase of O-H stretching signals in all of the cases. The observed chemical changes corresponded to the hydrolysis of esters presented in the pp films' structure.

Plasma printing - direct local patterning with functional polymer coatings for biosensing and microfluidics applications

We present a robust and flexible approach for the fabrication of chemical micropatterns of controllable dimension, based on the deposition of plasma-polymerized (pp) polymer films by using atmospheric-pressure plasma printing. In particular, the deposition of oxygen-rich organic pp films, aimed at the immobilization of biomolecules, is discussed. The maskless, fast and eco-friendly depositions present a line resolution from 50 μm to 250 μm, and a film thickness between 70 and 600 nm depending on the applied process parameters. Physico-chemical properties –such as morphology and functional groups– can be tailored to adjust a certain chemical platform suitable for multiple biosensing and microfluidic applications. The generated pp films are characterized by a saturated aliphatic-branched polymer structure with incorporated oxygen functionalities and a sufficient level of stability in aqueous environment. Furthermore, pp films provide an excellent reactivity towards amine-bearing molecules, which is exemplarily shown for the binding of acriflavine, a fluorescent dye.

Controlled co‐immobilization of biomolecules on quinone‐bearing plasma polymer films for multifunctional biomaterial surfaces

AbstractIn this study, an efficient methodology, allowing the controlled co‐immobilization of two complementary biomolecules, is reported for the production of multifunctional antibacterial surfaces. To promote long‐lasting covalent immobilization, metallic surfaces are first coated with a quinone‐bearing poly(methacrylate)‐based thin film by combining an atmospheric pressure liquid‐assisted plasma polymerization and a controlled sodium periodate‐induced catechol oxidation steps. The influence of the oxidation step on the film morphology and chemistry is investigated using an analytical multitool approach involving atomic force microscopy, ultraviolet, infrared, and X‐ray photoelectron spectroscopy techniques. Quartz crystal microbalance with dissipation monitoring (QCM‐D) analyses allow the rapid determination of the optimal biomolecule immobilization conditions in terms of kinetics of grafting and biomolecule solution concentrations. In vitro functional assays combined with QCM‐D analyses demonstrate promising, dual biologically active coated surfaces.

Alternating Current Electrical Characterization of Plasma Polymerized Pyrrole Thin Films

The alternating current (ac) electrical characterization of plasma polymerized pyrrole (PPPy) thin films have been discussed in this article. A parallel plate capacitively coupled glow discharge reactor was used to deposit PPPy thin films. To study the ac electrical conduction in the thin film, the variation of ac conductivity and dielectric constant of different thicknesses were investigated as the function of frequency and temperature. The observed frequency dependence of the ac conductivity is attributed to relaxations caused by the motion of electrons, which could be involved to hopping or tunneling between equilibrium sites. It is also concluded that, the ac conduction mechanism in PPPy thin films shows the correlated barrier hopping (CBH) model. The strong dependence of conductivity on frequency and the low activation energies of the carriers are also an indication of a hopping conduction mechanism at low temperatures. At high temperatures it may be due to the movements of thermally excited carriers from energy levels within the band gap. In conductivity vs temperature study a weak dependence of σac on temperature is observed which interprets the ac conduction mechanism as the hopping between localized states at the Fermi level. The observed frequency dependence of the dielectric constant in this study is attributed to the interfacial or space charge polarization and to the orientational polarization of molecular chains. On the other hand, the strong temperature dependence of dielectric constant at higher temperature and lower frequencies is attributed to the thermally activated electron hopping mechanism.

Physicochemical and Mechanical Performance of Freestanding Boron-Doped Diamond Nanosheets Coated with C:H:N:O Plasma Polymer.

The physicochemical and mechanical properties of thin and freestanding heavy boron-doped diamond (BDD) nanosheets coated with a thin C:H:N:O plasma polymer were studied. First, diamond nanosheets were grown and doped with boron on a Ta substrate using the microwave plasma-enhanced chemical vapor deposition technique (MPECVD). Next, the BDD/Ta samples were covered with nylon 6.6 to improve their stability in harsh environments and flexibility during elastic deformations. Plasma polymer films with a thickness of the 500–1000 nm were obtained by magnetron sputtering of a bulk target of nylon 6.6. Hydrophilic nitrogen-rich C:H:N:O was prepared by the sputtering of nylon 6.6. C:H:N:O as a film with high surface energy improves adhesion in ambient conditions. The nylon–diamond interface was perfectly formed, and hence, the adhesion behavior could be attributed to the dissipation of viscoelastic energy originating from irreversible energy loss in soft polymer structure. Diamond surface heterogeneities have been shown to pin the contact edge, indicating that the retraction process causes instantaneous fluctuations on the surface in specified microscale regions. The observed Raman bands at 390, 275, and 220 cm−1 were weak; therefore, the obtained films exhibited a low level of nylon 6 polymerization and short-distance arrangement, indicating crystal symmetry and interchain interactions. The mechanical properties of the nylon-on-diamond were determined by a nanoindentation test in multiload mode. Increasing the maximum load during the nanoindentation test resulted in a decreased hardness of the fabricated structure. The integration of freestanding diamond nanosheets will make it possible to design flexible chemical multielectrode sensors.

Understanding the dielectric and electrical transport behaviors of plasma polymerized diethanolamine thin films under alternating electric field

A capacitively coupled parallel plate glow discharge reactor has been utilized to develop plasma polymerized diethanolamine (PPDEOA) thin films to look into the alternating current (AC) features of PPDEOA thin films. It is observed that the dielectric constant, ɛ′ in PPDEOA thin films enhances by declining the frequency and that increases with increasing temperature. The AC electrical conductivity, σac is frequency dependent. The frequency exponent, s values are found to be 0.32 to 1.0 and 1.0 to 1.8 in the lower (102–103 Hz) and higher (>103 Hz) frequencies, respectively. These suggest the presence of hopping conduction in the lower frequency region and other mechanisms in the higher frequency region. The activation energies are derived to be 0.03 to 0.28 eV illustrating the less effect of temperature on them. The real part, M´ and imaginary part, M ̋ of electric modulus vary with frequency. The frequency dependent loss tangent, tanδ is obtained. The ɛ′, σac , and tanδ deviate by the virtue of film thicknesses.

Topological properties and direct current electrical charge transport mechanism of plasma polymerized cyclohexane thin films

High-performance plasma polymerized organic thin films have been synthesized by employing a capacitively coupled glow discharge technique and cyclohexane is used as a precursor material. The surface of the plasma polymerized cyclohexane (PPCHex) thin films observed to be smooth, pinhole free and uniform. It is observed from thermal analysis that the rate of loss of mass is very low in air atmosphere below 510 K and the films are thermally stable. Above 510 K weight loss takes place in different stages in air. The current density of the PPCHex thin films is increased when the thicknesses is decreased and that is increased with increasing temperatures. The conduction mechanism of carrier transport operative in these PPCHex thin film is dominated by Schottky type conduction mechanism. The activation energy of the PPCHex thin films for applied voltage 10 V is found 0.14 ± 0.05 eV near room temperature region and that in the higher temperature region is 0.57 ± 0.04 eV. The activation energy in the Schottky region for the applied voltage 50 V is about 0.16 ± 0.06 eV near the room temperature region and that is 0.83 ± 0.05 eV at the higher temperature region.

Fabrication and characterization of biorenewable plasma polymer films using sandalwood oil precursor

AbstractSandalwood oil is a natural, biorenewable oil which has many beneficial properties such as being anticarcinogenic and cytotoxic to some viruses, while being safe for human consumption. Therefore, thin films derived from sandalwood oil are of interest in the biomedical field. Here, thin films using sandalwood oil as the precursor are deposited via plasma polymerization with the aim of minimizing degradation of the precursor structure. The chemical properties of the plasma phase were measured by optical emission spectroscopy and the degradation pathways of the precursor molecules were elucidated via mass spectrometry. Combined with surface analysis of the thin films, partial structural retention of precursor molecules is demonstrated.

IR spectroscopic and photoluminescence studies of plasma polymerized organic thin films based on tea tree oil

Plasma-assisted synthesis of transparent, environment friendly, lightweight, flexible and stable organic thin films from naturally occurring precursors were emerging as potential candidates for organic semiconductor industry. In the present study, tea tree (Malaleuca alternifolia) oil based polymer thin films were deposited on glass and silicon substrate by using radio frequency plasma polymerization technique. The polymer thin films were characterized with atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy techniques. AFM images indicate the formation of homogenous film on the substrate surface. FTIR spectra gives bands related to methyl and methylene groups which confirms the formation of chain branching in the polymer films. Relatively intense infrared (IR) bands obtained from films deposited on glass substrate reveals that glass substrate is more favourable for the growth of polymers than silicon substrate. Optical band gap of the polymerized thin film on glass substrate was estimated using Tauc plot which gives a value of 3.19 eV, indicating the semiconducting nature of the material. Photoluminescence (PL) emission in the yellow region were observed from both the samples and its CIE colour coordinates also matches with yellow emission. Broad visible emission observed in the wavelength range 465–695 nm indicates the presence of multichromophores in the polymer film. Samples also gives IR emission in the wavelength range of 850–1090 nm, upon excitation with a wavelength of 785 nm contributed to polaronic transitions.

Development of Organic Gas Sensor Using Quartz Crystal Microbalance Coated with Plasma-polymerized Films

Development of Organic Gas Sensor Using Quartz Crystal Microbalance Coated with Plasma-polymerized Films

Design and characterization of a plasma chamber for improved radial and axial film uniformity

AbstractFilm uniformity is an issue in many deposition processes, especially in substrates with elongated lateral dimensions such as fibers. In this study, a plasma chamber was designed with dual electrodes to improve the uniformity of plasma polymer films. Plasma‐polymerized acrylic acid films were deposited via single‐electrode or double‐electrode configurations onto silicon wafer pieces placed at the center of the chamber to mimic the potential position of a fiber. A radial and spatial map of film chemistry and thickness throughout the chamber was determined which demonstrated improved radial uniformity and film stability using the dual‐electrode configuration, thus highlighting the importance of spatial characterization when designing a reactor for the coating of three‐dimensional objects such as fibers.

Investigating the stability of cyclopropylamine-based plasma polymers in water

Amino-rich thin coatings, known to show superior cell adhesion, proliferation and viability, are prepared in this study by means of plasma polymerisation. The Yasuda parameter (W/FM) is used as a scaling factor for the deposition of cyclopropylamine based plasma polymer films (CPA-PPFs) making use of a dielectric barrier discharge (DBD) operated at sub-atmospheric pressure. In this paper, the experimental research is focussed on the stability of the CPA-PPFs in water, a property of PPFs which is often overlooked in literature. More specifically, after their plasma-assisted fabrication, the polymerised samples are immersed in water for 24 h after which the coatings are chemically evaluated using Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy. The obtained results reveal that for all W/FM values under study water immersion results in a significant loss in CN/CN groups and a shift of primary to secondary/tertiary amines combined with the incorporation of oxygen at the surface as amides and alcohols/ethers. Moreover, FTIR, XPS chemical depth profiling (by means of C60 sputtering) and scanning electron microscopy (SEM) results also reveal that at W/FM values ≤ 288 MJ/kg, the PPFs are gradually dissolving during water immersion, while at W/FM values > 288 MJ/kg, the PPFs are delaminating from the substrate due to their high crosslinking degree. Nevertheless, cell-coating interaction studies reveal no signs of cytotoxicity 1 day after cell seeding and show that the thin coatings remaining on the substrate still strongly increase the adhesion of fibroblasts. In the near future, efforts will be undertaken to avoid the delamination from the substrate of the PPFs prepared at high W/FM values.

Functional Plasma Polymerized Surfaces for Biosensing.

The capabilities of biosensors for fast, economic, and user-friendly analysis of complex samples has led to the exploitation of analytical devices for detection, quantification, and monitoring of specific chemical species for various applications. For a sufficiently high surface reactivity toward the adopted bioreceptors, a thin functional layer is required to enable coupling of the target biomolecules and to provide good stability in the presence of a sample matrix. In this work, the generation of water-stable oxygen-rich plasma polymerized (pp) films deposited by atmospheric-pressure jet plasma for reliable immobilization of biomolecules is presented. Three types of pp films were developed and characterized. All of the obtained pp films were successfully used as a matrix layer in the SPR immunosensors, which provided excellent level of sensitivity, stability, and regenerability. The achieved results show that atmospheric pressure plasma-induced polymerization is a powerful alternative method for the preparation of matrix layers for a wide range of applications in the biological field.

How the dynamics of subsurface hydration regulates protein-surface interactions

The role of water structure near surfaces has been scrutinized extensively because it is accepted to control protein-surface interactions, however, often avoiding effects of hydration dynamics. Relating to this, we have recently discussed how the amount and state of water, accumulated within various hydrophobic-to-hydrophilic subsurface gradients of plasma polymer films, influence the magnitude of adsorbed bovine serum albumin, spurring the hypothesis of the presence of a subsurface dipolar field. This study now analyzes the kinetics of hydration by systematically introducing modified gradient architectures and relating different hydration times to the adsorption of a dipolar probing protein. We find that dry-stored subsurface gradients, owing nominally identical surface characteristics, exhibits comparable surface potential and protein adsorption values, while they behave in a different manner at transient hydration times of few hours, before reaching near-equilibrium state of the hydration. A characteristic hydration time is found where protein adsorption on gradient films is minimal, unveiling the transient nature of the effect. In general, protein adsorption is sensitive to the time allowed for hydration of the adsorbent surface, supporting our initial hypothesis inasmuch as the quantity as well as quality of water inside the subsurface matrix is crucial for controlling protein-surface interactions.

Improving the longevity of passive microfluidic systems through plasma polymer films with a vertical chemical gradient

Capillary driven microfluidic devices rely on hydrophilic surfaces to facilitate and control the fluid flow inside microchannels. This can be accomplished through the deposition of a highly functional plasma polymer film (PPF) on the surface of the device. Highly functional plasma polymer films exhibit ageing effects characterized by oxidation, degradation, swelling, dissolution, and restructuring at the surface to minimize the surface energy. The application of plasma polymer films in microfluidics is, therefore, limited by this instability. To overcome this limitation, plasma polymer films in the form of a vertical chemical gradient structure were deposited on the surface of microfluidic devices designed to perform immunodiagnostics for use during space missions. The vertical chemical gradient PPFs were composed of a highly cross-linked base layer with gradually less cross-linked and more functional surface layers. The highly cross-linked base layer of the gradient structure effectively hindered restructuring at the surface of the film, resulting in a more stable surface composition and surface wettability than that of the more traditional non-gradient structure. In addition, the microfluidics prepared using a gradient structure showed more stable chip runtimes. The stability of the gradient plasma polymer films will allow for their implementation in microfluidics, as well as a diverse range of biomedical applications such as drug delivery and the generation of antibacterial coatings.

Flexible Al2O3/plasma polymer multilayer moisture barrier films deposited by a spatial atomic layer deposition process

Al2O3/plasma polymer multilayers were developed and characterized for the moisture barrier films of flexible organic devices. The inorganic Al2O3 thin films were deposited by a spatial atomic layer deposition process and the organic layers were deposited by plasma polymerization in the same chamber using CHF3, benzene, and cyclohexane precursors. The deposition rate, light transmittance, and surface roughness of the plasma polymer films obtained from the three precursors were investigated. The three plasma polymer layers were introduced between Al2O3 layers and their effect on the water permeability and flexibility of each Al2O3/plasma polymer multilayer structure was evaluated. The multilayer structure with hydrocarbon from cyclohexane shows better flexibility than that with fluorocarbon by CHF3 and hydrocarbon by benzene. Polymer interlayers with plasma thicker than 20 nm are necessary for reasonable flexibility. The authors increased the number of layers up to 21 to improve the water permeability and flexibility. The water vapor transmission rate (WVTR) of a 100 nm-thick Al2O3/plasma polymer was reduced to 8.5 × 10−5 g/m2 day with the 21-layer structure. This WVTR value is 58% lower than that of the 100 nm-thick single-layer Al2O3. The WVTR of a 100 nm-thick single-layer Al2O3 increased by 900% when it was bent 1000 times with a bending radius of 1 cm due to film cracks, while, under the same conditions, the 21-layer structure showed only a 32% increase in the WVTR. These results indicate that the nanometer-scale-thick plasma polymer can be an effective solution for multilayer moisture barrier films.

Atmospheric Pressure Plasma Polymerized Oxazoline-Based Thin Films-Antibacterial Properties and Cytocompatibility Performance.

Polyoxazolines are a new promising class of polymers for biomedical applications. Antibiofouling polyoxazoline coatings can suppress bacterial colonization of medical devices, which can cause infections to patients. However, the creation of oxazoline-based films using conventional methods is difficult. This study presents a new way to produce plasma polymerized oxazoline-based films with antibiofouling properties and good biocompatibility. The films were created via plasma deposition from 2-methyl-2-oxazoline vapors in nitrogen atmospheric pressure dielectric barrier discharge. Diverse film properties were achieved by increasing the substrate temperature at the deposition. The physical and chemical properties of plasma polymerized polyoxazoline films were studied by SEM, EDX, FTIR, AFM, depth-sensing indentation technique, and surface energy measurement. After tuning of the deposition parameters, films with a capacity to resist bacterial biofilm formation were achieved. Deposited films also promote cell viability.

Degradable plasma polymer films with tailored hydrolysis behavior

Thin films based on polylactic acid have been prepared using plasma-assisted vacuum thermal deposition under varying RF glow discharge power and characterized in terms of chemical composition and structural homogeneity. As a measure of the degradability of the films their wash-off and hydrolysis behavior were monitored. The properties of the films were found to be tunable to a significant degree by the deposition conditions.

Humidity Robustness of Plasma-Coated PCBs

The reliability of printed circuit boards (PCB) is at risk due to continuous miniaturization. As a result, PCBs are more susceptible to external factors such as humidity, temperature, contamination, etc., which affect their general performance, leading to failure of electronic devices. Therefore, protection of the devices against these factors is gaining greatly in importance. Plasma polymerization is used as a method to form a protective barrier by applying plasma polymer films on PCBs. However, the humidity robustness of such plasma coatings on the PCB surface is unknown. In this work, several methods were used to characterize two types of plasma-coated PCBs based on 1H,1H,2H-perfluorodecyl acrylate precursor (single-layer and stacked coatings) upon exposure to humidity, temperature, and bias voltage. Modulated-temperature differential scanning calorimetry enabled thermal analysis of the plasma coatings. Electrochemical impedance spectroscopy in combination with the gravimetric moisture vapor sorption technique were used to study the interaction of these coatings with moisture and quantify the water uptake. The results revealed an only 2% increase of the capacitance of the coatings due to water uptake. Direct-current (DC) leakage current measurements were used to study the influence of a bias voltage applied between the electrodes on the coated PCBs upon exposure to cyclic climatic conditions. Electrical DC testing revealed the protective character of the stacked coating, which did not fail under the given stress conditions, in contrast to the single-layer plasma coatings.