ABSTRACT
Poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE)) ferroelectric nanotube arrays were fabricated using an anodized alumina membrane (AAM) as a template and silver electrodes were deposited on both the outer and inner sides of the nanotubes by an electroless plating method. The nanotubes have the unique structure of being sealed at one end and linked at the open end, thus preventing electrical shorting between the inner and outer electrodes. Compared with a P(VDF-TrFE) film with a similar overall thickness, the idealized nanotube array has a theoretical capacitance that is 763 times larger due to the greatly enlarged contact area between the electrodes and the polymer dielectric. A capacitance that is 95 times larger has been demonstrated experimentally, thus indicating that such nanotube arrays are promising for realizing high density capacitance and high power dielectric energy storage.
ABSTRACT
Electrochemical deposition is an attractive technique for the deposition of calcium phosphate, especially hydroxyapatite, on titanium implants. However, the adhesion of these coatings to the titanium substrates needs to be improved for clinical use. It is demonstrated that anodization of a titanium alloy does marginally increase the adhesion of calcium phosphate coatings. Although scratch test measurements on coatings deposited at a constant potential appear to suggest that adhesion improves with increased thickness of the anodized layer, when a constant current is used to deposit the coatings their adhesion becomes independent of the thickness of the anodized layer. This apparent contradiction is explained by the thicker oxides acting as larger series resistors that reduce the magnitude of the current density when deposition is conducted at a constant potential. The resulting lower current density is responsible for increased adhesion of the calcium phosphate coating. It was also observed that surface roughness affects the interfacial adhesion strength between the coating and the titanium substrate, with a more adherent coating being formed over a rough surface. However, adhesion becomes independent of surface finish at levels smoother than 600 grit, suggesting that mechanical interlocking is not the sole force at play.
