The crystallization process and its influence on the microstructures and in turn the ferroelectric and electromechanical properties of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer were investigated. It was found that, in addition to the crystallites formed at the isothermal crystallization temperature T x, further crystallites form during the rapid cooling from Tx to room temperature. The proportion of lower melting crystallites increases with Tx, and for Tx ) 142 °C, this proportion is more than 90%. The experimental results show that the lower melting crystallites have a higher fraction of the all-trans conformation (and thus more polar-phase component) than the crystallites formed at T x. As a result, the higher Tx samples show an increased polarization hysteresis and reduced electric field induced strain response. For example, the strain is reduced from -5.9 to -4.2% as T x is increased from 112 to 142 °C. In addition, the experimental results in combination with other reported results indicate that CFE units are included in the crystalline lattice. Consequently, the influence of CFE on the ferroelectric behavior of the polymer is through the defects induced in the crystal lattice.

This paper studies the effect of contact stress on friction and wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups by means of friction and wear joint simulator testing under serum lubrication. For a given applied load, increasing the contact stress by increasing the ball/socket radial clearance decreased both the coefficient of friction and the wear rate. Friction and wear were highly correlated. The dependence of friction on contact stress for the UHMWPE socket under serum lubrication was similar to that of semi-crystalline polymers under dry sliding. This finding indicates the occurrence of partial dry contact at asperity levels for the metal-polyethylene ball-in-socket joint under serum lubrication.

We investigate the influence of the composition, especially the chlorofluoroethylene content, on the ferroelectric and electromechanical properties of the poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene) (PVDF-TrFE-CFE). It was found that increasing the CFE from 0to9mol% gradually converts the normal ferroelectric of the copolymer (in the compositions range of VDF/TrFE mole ratio between 64∕36 to 75∕25) to a relaxor ferroelectric, resulting in a nearly hysteresis free polarization loop and high electrostrictive response. On the other hand, increasing CFE content causes reduction in crystallinity, which will affect the elastic modulus and the induced polarization level of the polymer. These competing effects determine the desired terpolymer compositions for given applications. The electromechanical strain as a function of induced polarization and macropolar phase fraction was modeled by a modified electrostrictive relation, which closely matches experimental data. It is found that the electrostrictive coefficient is relatively constant across the compositions investigated.