Search

The plasma-based surface modification of polymer materials with desirable bulk properties is a useful way to obtain polymers with tailor-made surface properties. This is necessary because the surface properties of most engineering polymers in use today are less then optimum for many applications. New functionalities such as biocompatibility, adhesion, special functional groups as well as lubricative, friction and wear-and-tear properties are demanded. By optimization of the process parameters during a low pressure plasma treatment, most of these requirements can be fulfilled. A specific functionalization with, e.g., carboxyl, amino, epoxy or hydroxyl groups as well as the generation of ultra thin layers with those functionalities is possible. The most challenging problem is not only to find parameters which do not lead to a fragmentation of the monomeric structure, but moreover the adhesion of the thin films to the substrates must overcome a stability test without delamination. To optimize plasma processes, with their great variety of parameters influencing the obtained surface properties, several surface analytical techniques are indispensable. XPS, AES as well as AFM are helpful tools to characterize the modified sample surfaces and consequently optimize the set of parameters for the glow discharge treatment. With XPS the retention of the monomer structure can be controlled. AES depth profiling clarifies the elemental composition of gradient layers, necessary for a good adhesion of scratch-resistant coatings. AFM visualizes the surface morphology which is important for, e.g., the friction properties of plasma-coated substrates. [ABSTRACT FROM AUTHOR]

Abstract: In conventional plasma polymerization processes, the bulk properties of the treated substrates are maintained whereas the surface properties are changed to the ones of the coating polymer. In contrast, materials with ultrathin non-closed layers and domains of plasma deposited compounds can show combined properties (from the surface of the bulk material and the non-closed layer) or even completely new behavior. This can be seen by analyzing e.g. the wettability (contact angle), the tribological properties, chemical functionalities or biological interactions. Ultrathin closed and non-closed films (domains) of fluorocarbon polymer were produced by means of RF-CVD (radio frequency aided chemical vapor deposition, plasma polymerization) with CHF3 as monomer gas; argon was added as additional process gas. Our work has been carried out in a symmetric capacitively coupled reactor at 13.56 MHz in the low-pressure, glow-discharge regime. The influence of pulsing the plasma by varying on- and off-times on the surface properties were investigated on silicon wafers as substrates. The obtained functionalized surfaces were characterized by means of advancing and receding contact angle measurements, X-ray photoelectron spectroscopy (XPS) as well as atomic force microscopy (AFM). [Copyright &y& Elsevier]