Poly(L-lactic acid) (PLLA) samples were prepared with different degrees of crystallinity, obtained during cooling from the melt at different scanning rates, and subjected to annealing below Tg. For intermediate crystallinities two endothermic peaks assigned to enthalpy recovery could be detected by differential scanning calorimetry (DSC) on heating, indicating the existence of two distinct glass transition dynamics. The morphology at different length scales was characterized using WAXS, SAXS, and polarized light microscopy to correlate the DSC results to the microstructure. The low-temperature process was assigned to the bulklike glass transition whereas the high-temperature one was attributed to the restricted motions of the amorphous phase confined by the crystalline structures. The position and broadness of the two endotherms were found to be essentially independent of the spherulitic content of the samples. This was related to the invariance of the lamellar morphology within a large range of degrees of crystallinity. The occurrence of the high-temperature process throughout such range allowed to attribute this process to the hindered motions of the mobile amorphous phase within the lamellar stacks.

Due to the large potential of electroactive materials in novel tissue engineering strategies, the aim of this work is to determine if the crystalline phase and/or the surface electrical charge of electroactive poly(vinylidene fluoride), PVDF, have influence on the biological response in monolayer cell culture. Non-polar α-PVDF and electroactive β-PVDF were prepared. The β-PVDF films were poled by corona discharge to show negative or positive electrical surface charge density. It has been concluded that hydrophilicity of the PVDF substrates depends significantly on crystalline phase and

Poly(vinylidene fluoride) (PVDF) microparticles have been produced by electrospraying as a suitable substrate for tissue engineering applications. The influence of the polymer solution concentration and processing parameters, such as electric field, flow rate and inner needle diameter, on microparticle size and distribution has been studied. Polymer concentration is the most influential parameter on PVDF microparticle formation. Higher concentrations promote the formation of fibers while dilute or semi dilute concentrations favor the formation of PVDF microparticles with average diameters ranging between 0.81 AE 0.34 and 5.55 AE 2.34 mm. Once the formation of microparticles is achieved, no significant differences were found with the variation of other electrospray processing parameters. The electroactive b-phase content, between 63 and 74%, and the crystalline phase content, between 45 and 55%, are mainly independent of the processing parameters. Finally, MC-3T3-E1 cell adhesion on the PVDF microparticles is assessed, indicating their potential use for biomedical applications.

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The dielectric properties of biaxially stretched polyethylene terephthalate (PET) films of thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequency range Hz and the temperature range C. Differencial scanning calorimetry (DSC), in the range C, was employed to investigate the thermal properties of the PET samples. Besides measuring the relaxation associated with the glass transition and the secondary relaxation, special attention has been paid to the investigation of DC-conductivity-related effects. They give rise to high dielectric permittivity values and dielectric losses at low frequencies and high temperatures. The results are analysed within the complex permittivity formalism and discussed in terms of interfacial Maxwell - Wagner - Sillars polarization, the peak, conductivity relaxation, space-charge polarization, electrode polarization and DC conductivity. DC conductivity values determined from frequency plots of the AC conductivity follow the Vogel - Tamman - Fulcher equation at temperatures higher than the glass transition temperature, indicating that the charge-carrier transport mechanism is governed by the motion of the polymeric chains. On the basis of the temperature dependence of the DC conductivity PET is classified as a fragile system.

A phenomenological model for the process of structural relaxation in glass-forming materials is discussed. The model is based on an expression for the evolution of the configurational entropy of the material when subjected to an arbitrary thermal history and contains four fitting parameters. The prediction of the model is presented in terms of heat capacity cp(T) curves, which are compared with the experimental DSC heating scans. Experimental results on polycarbonate with a broad series of thermal histories are presented, and the routine employed to fit the parameters of the model is described. The procedure permits the determination of material parameters (independent of thermal history) of the polymer: a curve of calorimetric equilibrium relaxation times as a function of temperature and a value for the width parameter of the Kohlrausch-Williams-Watts relaxation function. The possibility that the limit states of the structural relaxation process do not coincide with the states obtained from the extrapolation of the experimentally determined liquidus curve is also discussed.

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