Local piezoelectric response of single poly(vinylidene fluoride) electrospun fibers

It is shown that electrospun poly(vynilidene fluoride) nanofibers are fully poled right after preparation and show b-phase contents of 70%, therefore being able to be implemented into electroactive devices without further processing steps. Further,the local piezoelectric properties of individual electrospun fibers have been studied by piezoresponse force microscopy. Piezoelectric response, polarization switching, and nanoscale patterning of the fibers have been demonstrated.

Osteoblast, fibroblast and in vivo biological response to poly(vinylidene fluoride) based composite materials

Electroactivematerials can be taken to advantage for the development of sensors and actuators as well as for novel tissue engineering strategies. Composites based on poly(vinylidenefluoride),PVDF,have been evaluated with respect to their biological response. Cell viability and proliferation were performed in vitro both with Mesenchymal Stem Cells differentiated to osteoblasts and Human Fibroblast Foreskin 1. In vivo tests were also performed using 6-week-old C57Bl/6 mice. It was concluded that zeolite and clay composites are biocompatible materials promoting cell response and not showing in vivo pro-inflammatory effects which renders both of them attractive for biological applications and tissue engineering, opening interesting perspectives to development of scaffolds from these composites. Ferrite and silver nanoparticle composites decrease osteoblast cell viability and carbon nanotubes decrease fibroblast viability. Further, carbon nanotube composites result in a significant increase in local vascularization accompanied an increase of inflammatory markers after implantation.

Thermomechanical environment characterisation in injection moulding and its relation to the mechanical properties of talc-filled polypropylene

This study is focused on the establishment of relationships between the injection moulding processing conditions, the applied thermomechanical environment (TME) and the tensile properties of talc-filled polypropylene,adopting a new extended concept of thermomechanical indices (TMI). In this approach, TMI are calculated from computational simulations of the moulding process that characterise the TME during processing, which are then related to the mechanical properties of the mouldings. In this study, this concept is extended to both the filling and the packing phases, with new TMI defined related to the morphology developed during these phases. A design of experiments approach based on Taguchi orthogonal arrays was adopted to vary the injection moulding parameters (injection flow rate, injection temperature, mould wall temperature and holding pressure), and thus, the TME. Results from analysis of variance for injection-moulded tensile specimens have shown that among the considered processing conditions, the flow rate is the most significant parameter for the Young’s modulus; the flow rate and melt temperature are the most significant for the strain at break; and the holding pressure and flow rate are the most significant for the stress at yield. The yield stress and Young’s modulus were found to be governed mostly by the thermostress index (TSI, related to the orientation of the skin layer), whilst the strain at break depends on both the TSI and the cooling index (CI, associated to the crystallinity degree of the core region). The proposed TMI approach provides predictive capabilities of the mechanical response of injection-moulded components, which is a valuable input during their design stage.

On the origin of the electrical response of vapor grown carbon nanofiber + epoxy composites

The origin of the electrical response of vapor grown carbon nanofiber (VGCNF) + epoxy composites is investigated by studying the electrical behavior of VGCNF with resin, VGCNF with hardener and cured composites, separately. It is demonstrated that the onset of the conductivity is associated to the emergence of a weak disorder regime. It is also shown that the weak disorder regime is related to a hopping depending on the physical properties of the polymer matrix.

Determinants of environmental disclosure in the annual reports of large companies operating in Portugal

Similarly to what has happened in other countries, since the early 1990s Portuguese companies have developed corporate environmental reporting practices in response to internal and external factors. This paper is based on empirical research directed to both the study of environmental reporting practices developed by Portuguese companies and the identification of the factors that explain the extent to which these companies disclose environmental information. This study focuses on the environmental disclosures made in the annual reports by a sample of 109 large firms operating in Portugal during the period 2002-04. Using the content analysis technique we have developed an index in order to assess the presence of the environmental disclosures in companies’ annual reports and their breadth. Based on the extant literature, several characteristics relating to firms’ attributes were selected and their influence on the level of environmental disclosure was tested empirically. The selected explanatory variables were firm size, industry membership, profitability, foreign ownership, quotation on the stock market and environmental certification. The results reveal that, in spite of the fact that the level of environmental information disclosed during the period 2002-04 is low, the extent of environmental disclosure has increased as well as the number of Portuguese companies that disclose environmental information. Moreover, the firm size and the fact that a company is listed on the stock market are positively related to the extent of environmental disclosure. This study adds to the international research on environmental disclosure by providing empirical data from a country, Portugal, where empirical evidence is still relatively unknown, extending the scope of the current understanding of the environmental reporting practices.

The influence of matrix mediated hopping conductivity, filler concentration, aspect ratio and orientation on the electrical response of carbon nanotube/polymer nanocomposites

A model to simulate the conductivity of carbon nanotube/polymer nanocomposites is presented. The proposed model is based on hopping between the fillers. A parameter related to the influence of the matrix in the overall composite conductivity is defined. It is demonstrated that increasing the aspect ratio of the fillers will increase the conductivity. Finally, it is demonstrated that the alignment of the filler rods parallel to the measurement direction results in higher conductivity values, in agreement with results from recent experimental work.