The effects of various processing conditions, like annealing, poling, mechanical rolling and their combinations, on the dielectric and ferroelectric properties of PVDF [poly(vinylidene fluoride)] were systematically studied in this work. Further, the effect of processing sequence on the structure and properties was investigated. While all the processing conditions adopted here resulted in phase transformation of the α- to electroactive β-polymorph in PVDF, the fraction of β-phase developed was observed to be strongly contingent on the adopted process. The transformation of α to electroactive β-polymorph was determined by X-ray diffraction and FTIR. The neat PVDF showed only α-phase, whereas mechanically rolled samples exhibited the highest ca. 85% β-phase in PVDF. Both the permittivity and the loss tangent decreased in the samples which had undergone different processing conditions. The polarization-electric field (P-E) loops for all the samples were evaluated. Interestingly, the energy density, estimated from the electrical displacement-electric field (D-E) loops, was observed to be highest for the poled samples which were initially rolled. The results indicate that various processing conditions can influence the dielectric and the ferroelectric properties differently.

No abstract

Crystallization-induced phase separation and segmental relaxations in poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends was systematically investigated by melt-rheology and broadband dielectric spectroscopy in the presence of multiwall carbon nanotubes (MWNTs). Different functionalized MWNTs (amine, -NH2; acid, -COOH) were incorporated in the blends by melt-mixing above the melting temperature of PVDF, where the blends are miscible, and the crystallization induced phase separation was probed in situ by shear rheology. Interestingly, only -NH2 functionalized MWNTs (a-MWNTs) aided in the formation of β-phase (trans-trans) crystals in PVDF, whereas both the neat blends and the blends with -COOH functionalized MWNTs (c-MWNTs) showed only α-phase (trans-gauche-trans-gauche') crystals as inferred from wide-angle X-ray diffraction (WXRD) and Fourier transform infrared (FTIR). Furthermore, blends with only a-MWNTs facilitated in heterogeneous nucleation in the blends manifesting in an increase in the calorimetric crystallization temperature and hence, augmented the rheologically determined crystallization induced phase separation temperature. The dielectric relaxations associated with the crystalline phase of PVDF (αc) was completely absent in the blends with a-MWNTs in contrast to neat blends and the blends with c-MWNTs in the dielectric loss spectra. The relaxations in the blends investigated here appeared to follow Havriliak-Negami (HN) empirical equations, and, more interestingly, the dynamic heterogeneity in the system could be mapped by an extra relaxation at higher frequency at the crystallization-induced phase separation temperature. The mean relaxation time (τHN) was evaluated and observed to be delayed in the presence of MWNTs in the blends, more prominently in the case of blends with a-MWNTs. The latter also showed a significant increase in the dielectric relaxation strength (Δε). Electron microscopy and selective etching was used to confirm the localization of MWNTs in the amorphous phases of the interspherulitic regions as observed from scanning electron microscopy (SEM). The evolved crystalline morphology, during crystallization-induced phase separation, was observed to have a strong influence on the charge transport processes in the blends. These observations were further supported by the specific interactions (like dipole induced dipole interaction) between a-MWNTs and PVDF, as inferred from FTIR, and the differences in the crystalline morphology as observed from WXRD and polarized optical microscopy (POM).

Background: Longitudinal, patient-level data on resource use and costs after an ischemic stroke are lacking in Canada. The objectives of this analysis were to calculate costs for the first year post-stroke and determine the impact of disability on costs. Methodology: The Economic Burden of Ischemic Stroke (BURST) Study was a one-year prospective study with a cohort of ischemic stroke patients recruited at 12 Canadian stroke centres. Clinical history, disability, health preference and resource utilization information was collected at discharge, three months, six months and one year. Resources included direct medical costs (2009 CAN$) such as emergency services, hospitalizations, rehabilitation, physician services, diagnostics, medications, allied health professional services, homecare, medical/assistive devices, changes to residence and paid caregivers, as well as indirect costs. Results were stratified by disability measured at discharge using the modified Rankin Score (mRS): nondisabling stroke (mRS 0-2) and disabling stroke (mRS 3-5). Results: We enrolled 232 ischemic stroke patients (age 69.4 ± 15.4 years; 51.3% male) and 113 (48.7%) were disabled at hospital discharge. The average annual cost was $74,353; $107,883 for disabling strokes and $48,339 for non-disabling strokes. Conclusions: An average annual cost for ischemic stroke was calculated in which a disabling stroke was associated with a two-fold increase in costs compared to NDS. Costs during the hospitalization to three months phase were the highest contributor to the annual cost. A "back of the envelope" calculation using 38,000 stroke admissions and the average annual cost yields $2.8 billion as the burden of ischemic stroke.RÉSUMÉ: Impact du degré d'invalidité sur les coûts reliés à l'accident vasculaire cérébral ischémique au cours de la première année au Canada. Contexte : Nous n'avons pas de données longitudinales sur l'utilisation des ressources par les patients et les coûts ainsi engendrés suite à un accident vasculaire cérébral (AVC) ischémique au Canada. Les buts de cette analyse étaient de calculer les coûts engendrés au cours de la première année après un AVC et de déterminer l'impact de l'invalidité sur ces coûts. Méthode : Le Economic Burden of Ischemic Stroke (BURST) Study est une étude prospective d'une durée de un an chez une cohorte de patients ayant subi un AVC ischémique qui ont été recrutés dans 12 centres canadiens de traitement de l'AVC. Des informations ont été recueillies sur l'histoire clinique, l'invalidité, les choix de santé et l'utilisation des ressources au moment du congé hospitalier, trois mois, six mois et un an plus tard. Les ressources incluaient les coûts médicaux directs (en $ canadiens 2009) comme les services d'urgence, les hospitalisations, la réadaptation, les frais médicaux, diagnostiques et thérapeutiques, les autres services professionnels, les soins à domicile, les équipements médicaux/accessoires fonctionnels, les changements effectués au lieu de résidence et les aidants rémunérés ainsi que les ...