Ethyl lactate is injected into a dielectric barrier discharge (DBD) to build up a degradable plasma polymer (PP) to be used as a drug delivery system. Plasma power, deposition time, and type of carrier gas (Ar, N 2 ) are correlated to the coating in vitro degradation rate. PPs are characterized by AFM, SEM, IR spectroscopy, XPS, and SEC, while surface profilometry is used to monitor the degradation kinetics. PPs deposited under N 2 are mainly composed of hydrophilic functionalities, which explain their fast degradation upon exposure to an aqueous environment. In contrast, PPs synthesized under Ar lead to a slower degradation rate due to their hydrocarbon structure containing some hydrolyzable moieties. The potential of the PPs for vascular applications is verified through cell viability experiments.

The influence of the input voltage frequency (35 and 150 kHz), interelectrode gap (1 and 2 mm) and precursor concentration (250, 350, and 450 ppm) on the electron temperature (Te), number density of metastable Ar atoms (n(Ar m )), and discharge current density (proportional to the electron density ne) is studied in an argon-ethyl lactate dielectric barrier discharge (DBD). An argon-ammonia Penning mixture is also considered as reference. These results are correlated to the chemistry (XPS, IR) and topography (AFM) of the ethyl-lactate-based plasma polymer coatings. Low Te values from 0.3 to 0.5 eV were obtained for all discharges. This observation, in addition to resemblances with the Ar-NH3 mixture, suggested that the ionization kinetics of ethyl lactate-based discharges is driven by Penning reactions. Among the investigated parameters, the dissipated power obtained through changes of the excitation frequency had the largest impact on both the coatings properties and the discharge behavior.

A combination of optical emission spectroscopy and collisional-radiative modelling is used to determine the time-resolved electron temperature (assuming Maxwellian electron energy distribution function) and number density of Ar 1s states in atmospheric pressure Ar-based dielectric barrier discharges in presence of either NH3 or ethyl lactate. In both cases, Te values were higher early in the discharge cycle (around 0.8 eV), decreased down to about 0.35 eV with the rise of the discharge current, and then remained fairly constant during discharge extinction. The opposite behaviour was observed for Ar 1s states, with cycle-averaged values in the 10 17 m −3 range. Based on these findings, a link was established between the discharge ionization kinetics (and thus the electron temperature) and the number density of Ar 1s state.

By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (Te) and number density of argon metastable atoms (n(Ar m)) were determined in argon-ethyl lactate dielectric barrier discharges. The influence of a square pulse power supply on Te, n(Ar m), and the discharge current is evaluated and correlated to the chemistry and the topography of the plasma-deposited coatings. Pulsed discharges were found to have shorter (100 ns) but stronger (1 A) current peaks and higher electron temperatures (0.7 eV) than when using a 35 kHz sinusoidal power supply (2 µs, 30 mA, 0.3 eV). The n(Ar m) values seemed rather stable around 10 11 cm-3 with a sinus power supply. On the contrary, with a pulse power supply with long time off (i.e. time without discharge) between each pulse, a progressive increase of n(Arm) from 10 11 cm-3 up to 10 12-10 13 cm-3 was observed. When the time off was reduced, these increases were measured in sync with the current peak. The chemical composition of the coatings was not significantly affected by using a pulse signal whereas the topography was strongly influenced and led to powder formations when reducing the time off.

Due to their chemical inertness and low friction coefficient, fluoropolymers are today widely employed in sectors of activity as diverse and distinct as the textile industry, architectural sector, and medicine. However, their low surface energy results in poor adhesion, for example, when used for a component in a composite device with multiple other materials. Among the techniques used to enhance their adhesion, atmospheric pressure discharges provide a fast and low-cost method with a reduced environmental impact. Although this approach has proven to be efficient, the different chemical and physical processes in the discharge remain not fully understood. In this study, fluoropolymer surfaces were modified using an atmospheric pressure dielectric barrier discharge in a nitrogen and organic precursor environment. To prevent any damage to fluoropolymer surfaces, the dissipated power in the discharges was tuned by applying a duty cycle. Evidence shows that plasma treatment allows for the incorporation of oxygen and nitrogen in the surface resulting in the formation of hydrophilic functionalities such as carbonyl groups both in ketone and amide form, amine, and hydroxyl groups after 180 s of treatment. Overall, the data reveal that the discharge duty cycle has more effect on the oxygen and carbon content in the coating than the precursor concentration. In addition, increasing the precursor concentration limits the molecular fragmentation and nitrogen incorporation into the coating. These experiments enable the building of a better fundamental understanding of the formation mechanism of such chemical moieties at the fluoropolymer surface.

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