Surface properties, radiofrequency plasmas

This chapter aims to discuss and summarize theoretical and practical aspects of such plasma interfaces, presenting the existing examples from our own recent work on plasma electrochemical reactions between typical ionic liquids and plasmas. First, we address the plasma state and essential properties with respect to its application in electrochemistry. Today, low temperature plasmas - mostly in the form of radiofrequency or microwave plasmas - play an important role in the treatment or modification of solid surfaces. However, as plasma chemistry is usually not an element of chemistry curricula, we include a very brief introduction but refer the reader to the literature for more detailed information. 

Chemically modified celluloses have been analyzed by conventional wet methods and by various Instrumental methods designed to differentiate bulk and surface properties. Electron emission spectroscopy for chemical analyses (ESCA) used alone and In combination with radiofrequency cold plasmas yielded elemental analyses, oxidative states of the element, and distribution of the element. Techniques of electron paramagnetic resonance (EPR), chemiluminescence, reflectance infrared spectroscopy, electron microscopy, and energy dispersive X-ray analyses were also used to detect species on surfaces and to obtain depth profiles of a given reagent in chemically modified cottons. 

Among the different types of pretreatment methods proposed, plasma treatment represents probably the most versatile and efficient method for surface modification. The properties of plasma-modified surfaces mainly depend on parameters controlled by the reaction conditions (i.e., type of gas, pressure, radiofrequency, effective power, and time of treatment) and by the physicochemical properties of the polymer used. By using short plasma treatments, the surface modification can be confined to the first atomic layers of the polymer surface. Moreover, plasma treatment offers the ability to choose the nature of the chemical modification as a function of the gas used. As an example, the introduction of amine functionalities on PHB surfaces has been achieved using ammonia plasma [47, 51]. However, the number of functional groups formed at the surface is difficult to control. 

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