Polymers ion-implanted

If the Fermi level is at an energy such that the electronic states are extended, then finite conductivity at zero temperature is expected. This model assumes that the substantial disorder is homogeneous through the isotropic three-dimensional sample. Other external parameters such as magnetic field or pressure can affect the localization/delocalization transition and the localization lengths. This model has received much experimental attention for doped and ion implanted polymers [2,49], although more recent studies of ion-implanted rigid rod and ladder polymers reveals a three-dimensional semimetallic conductor with weak localization effects [50]. 

These include the effect of the processing conditions on the mechanical properties of synthetic and natural polymers, the characterization of ion-implanted polymer surfaces, the study of mechanical changes in polymer implants after wear, the influence of coatings on surface properties, weatherability characterization of polymers, etc. 

To explore the behaviour of ion-implanted polymers microfriction studies were conducted on 1 MeV Ar" " implanted PEEK, and PS implanted to fluences of 5, 10 and 50 x 10 ions m (Rao et al, 1995). The results were compared with macrofriction values obtained using standard pin-on-disc-type tests. The polymers were also characterized for surface mechanical properties using the nanoindentation technique. The most striking aspect of the microfriction tests on the ion-implanted polymers is a marked stick-slip behaviour, which was not observed for the non-irradiated polymers. 

Valenza, A. Visco, A.M. Torrisi, L. Campo, N. Characterization of ultra-high-molecular-weight polyethylene (UHMWPE) modified by ion implantation. Polymer 2004, 45, 1707-1715. 

Ion implantation. Polymers, when exposed to proper ion beams, can become conducting due to the implantation of ions in the polymer s lattice, which form covalent bonds with the material. The doping level depends on the energy of the ion beam. 

The formation of surface pores, the changes in the polar component of the surface free energy, and the disruption and formation of centers of specific adsorption in the course of ion bombardment considerably affect the cell adhesion at the ion-implanted polymers, which opens up new possibilities for controlling the biocompatibility of polymer materials [76,77]. Thus the changes in the dynamics of plasma protein adsorption at silicon rubber upon implantation with 150-keV, ... 

Tauc plot [81], // is the number of benzoid rings that form the cluster, and /3 is the resonance integral (Hiickel theory gives jS = 2,9 eV). The fluence dependence of g for ion-implanted polymers can usually be fitted with an exponential function,... 

The values of t (i.e., the critical exponent for electrical conductivity versus fluence), obtained from the slope of logftr) versus log(4> - j) linear dependences for various ion-implanted polymers (polyacrylonitrile [11], polyimide [87], poly-2,6-dimethyl-polyphenyleneoxide [11], perylene derivatives [12]), are 4-5 when the energy is deposited predominantly by the collisional mechanism and 7-8 when electronic stopping prevails. These values of the critical exponent for conductivity are substantially higher than those observed for metal nanoparticles in a dielectric matrix [88], which can be apparently explained by the effects of the conducting phase ordering during the implantation. 

Studies of the temperature dependence of ESR line shape in vacuum and under different oxygen pressures provide some further information on the transport properties of the ion-implanted polymers [102,107,108]. These studies have shown that... 

With anodic polarization and in contact with an indifferent electrolyte, ion-implanted polymers readily lose electrochemical activity due to oxidation of the carbonaceous conducting phase. With carbon electrode materials, the anodic reactions proceed via the formation of adsorbed hydroxyl radicals [110] followed by their electrochemical desorption, which can be accompanied by the liberation of either CO2 (destructive pathway) or oxygen (nondestructive pathway) ... 

Slow degradation of the conducting carbonaceous phase, resulting in electrode deactivation, also occurs when oxidation of the redox species proceeds at the surface of ion-implanted polymers. 

Wasserman, B., Fractal nature of electrical conductivity in ion-implanted polymers, Phys. Rev. B, 34, 1926-1931 (1986). 

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