Nano-scaled carbon fillers and their functional polymer composites

The manufacturing of low density conductive plastics, that could replace metals in many applications, is a challenging target that has been pursued by several technological segments. The incorporation of carbon nanofillers, namely carbon nanotubes and graphene, into a polymer matrix is a recent and promising approach. The achievement of highly conductive nanocomposites, with low electrical percolation threshold, depends mostly on the intrinsic properties of the fillers and their state of dispersion throughout the matrix. In this system the macroscopic properties of the composite are undoubtedly governed by the nature and extension of the interactions between filler particles, as well as between filler and polymer matrix. This doctoral dissertation therefore examines the macroscopic electrical behavior of carbon fillers, at initial stage, still as a powder, and subsequently when inserted into polymer matrix to form conductive nanocomposites. The latex technology has proven to be efficient on promoting a homogenous incorporation of exfoliated CNTs into any kind of viscous polymer which can be artificially brought into latex form, or which can be synthetized via emulsion polymerization. One objective of this dissertation is henceforth to study the scope and limitations of multifunctional graphene-based nanocomposites, using the superior DPI-owned water-based latex concept developed for CNTs, for dispersing the two-dimensional graphene nanofiller in polymer matrices (PS, PP, PS/PPO). For comparison, zero-dimensional (statistically spherical) carbon black nanoparticles, one-dimensional MWCNTs, and three-dimensional graphite are also evaluated. We strive to understand differences observed for the different carbon allotropes, each with a high surface-to-volume ratio Special attention is given to graphene as nanofiller, whose properties may be highly variable depending on the preparation method. In order to assess a collective understanding of the main routes utilized in this work for preparation of graphene, Chapter 2 introduces a systematic literature review on the particularities of each preparation method. Techniques used for characterization of single sheet properties and its organization inside polymer composites are presented, with focus on atomic force microscopy and Raman spectroscopy. The conductive performance of a composite is directly related to the formation of a conducting network through the polymer matrix and its understanding depends critically on the knowledge of the electrical behavior of the agglomerated nanoparticles, e.g. in the form of a bulk powder or a paper film. In literature there is still a lack of information concerning these macroscopic bulk properties of carbon powders. Chapter 3 studies the electrical conductivity of the nanofillers MWCNTs, graphene, carbon black and graphite, using compacts produced by a paper preparation process and by powder compression. Powder pressing assays show that the bulk conductivity depends not only on the intrinsic material properties but is also strongly affected by the number of particle contacts and the packing density. Conductivities at high pressure (5 MPa) for the graphene, nanotube and carbon black show lower values (~102 S/m) as compared to graphite (~103 S/m). For nanotube, graphene and graphite particles, the conductive behavior during compaction is governed by mechanical particle arrangement/deformation mechanisms while for carbon black this behavior is mainly governed by the increasing particle contact area. The materials resulting from the paper preparation process for carbon black and graphite showed similar conductivity values as for the compacts, indicating a limited effect of the surfactant on the conductivity. The paper preparation process for the large surface area nanotube and graphene particles induces a highly preferred in-plane orientation, thereby yielding largely the single particle intrinsic conductivity for the in-plane direction, with values in the order of 103 S/m. In Chapter 4, the percolation thresholds and final conductivities of polypropylene (PP) composites, prepared with the fillers studied in Chapter 3, are evaluated and compared with powder and paper results. The latex technology concept is used for the incorporation of the carbon fillers in the polymer. The fillers are first dispersed in water (assisted by surfactants) using ultra-sonication, subsequently mixed with PP latex, then freeze-dried and, finally, hot-pressed into composite tablets. PP composites produced in this work showed well-dispersed fillers inside the polymer, with percolation thresholds as low as 0.3 wt.%. The maximum conductivity obtained for the composites is approximately ~1 S/m, not reaching the high value of ~103 S/m, which are obtained for graphene and nanotube-based paper films or graphite compacts. Chapter 5 focuses on the characterization of graphene layers via micro-Raman spectroscopy, tip-enhanced Raman spectroscopy (TERS) and tip-enhanced Raman spectroscopy mapping (TERM). In particular TERM allows for the investigation of individual graphene sheets with high Raman signal enhancement factors and allows imaging of local defects with nanometer resolution. Enhancement up to 560% of the graphene Raman bands intensity was obtained using TERS. TERM (with resolution better than 100 nm) showed an increase in the number of structural defects (D band) on the edges of both graphene and graphite regions. Continuing the investigation of graphene structures, Chapter 6 compares graphene sheets produced from graphite powder using the three best known water-based conversion approaches. The first two are based on chemical oxidation methods, only differing in the reduction process, either by the use of hydrazine or by thermal expansion, respectively. The third one is based on long-term ultrasonic exfoliation. Water/surfactant solutions were prepared with these three nanofillers and latex technology was applied for the preparation of conductive graphene/polystyrene composites with well-dispersed graphene platelets. The samples were characterized with respect to filler properties and morphology, and their influences on electrical conductive properties of the composites were compared. Microscopic studies showed that both reduction processes lead to agglomeration/wrinkling of the nanoplatelets, even though they yield composites with high conductivity and low percolation threshold. Although mechanical ultrasound exfoliation of graphite produces less defective multi-layer graphene, these platelets have a smaller lateral size and their composites exhibit a higher percolation threshold. As a final attempt, in Chapter 7, the concept of liquid-phase dispersion, inspired on the latex technology, was applied for the preparation of well-dispersed suspensions of multi-wall carbon nanotubes and graphene in chloroform, using long-time ultra-sonication, without the use of surfactants. The dispersions with pre-defined filler concentration (0.5 mg/ml) were monitored via UV-Vis until the achievement of optimum exfoliation (6 h). The mixture of the filler suspensions with a PS/PPO solution, both using chloroform as solvent, subsequent drying and hot pressing, yielded for most of the samples a visually homogeneous and shiny black composite tablet. The well-dispersed organization of the fillers inside the polymer matrix, visualized with scanning electron microscopy, resulted in ultimate conductivities and percolation thresholds of 57 S/m and 0.2 wt.% for nanotubes composites, and 0.9 S/m and ~1 wt.% for graphene composites, respectively. Dynamic mechanical analysis showed that an increase in the storage moduli of the PS/PPO matrix could be gradually obtained by the insertion of fillers, e.g. reaching ~30% of enhancement by the addition of 3 wt.% of graphene filler. The same trend in improvement, at lower augmentation, was observed for the corresponding nanotubes-based composites

Asymmetric information in the regulation of the access to markets

It is frequently argued that the high costs of clinical trials prior to the admission of new pharmaceuticals are stifling innovation. At the same time, regulation of the access to markets is often justified on the basis of consumers` inability to detect the true quality of a product. We examine these arguments from an information economic perspective by setting a framework where the incentives to invest in R&D are influenced by the information structure prevailing when the product is launched in the market at a later stage. In this setting, by changing the information structure, regulation (or the lack of) can thus indirectly affect R&D efforts. More formally, we construct a moral hazard - cum - adverse selection model in which a pharmaceutical firm exerts an unobservable effort towards developing an innovative (high quality) drug (moral hazard) and then announces the (unobservable) quality outcome to an uninformed regulator and/or consumers (adverse selection). We compare the outcomes in regard to innovation effort and expected welfare under two regimes: (i) regulation, where products undergo a clinical trial designed to ascertain product quality at the point of market access; and (ii) laissez-faire with free entry, where the revelation of quality is left to the market process. Results show that whether or not innovation is greater in the presence of entry regulation crucially depends on the efficacy of the trial in identifying (poor) quality, on the probability that unknown qualities are revealed in the market process, and on the preference and cost structure. The welfare ranking of the two regimes depends on the differential effort incentive and on the net welfare gain from implementing full information instantaneously. For example, in settings of vertical monopoly, vertical differentiation and horizontal differentiation with no variable cost of quality, entry regulation tends to be the preferred regime if the effort incentive under pooling is relatively low and profits do not count too much towards welfare. A complementary numerical Analysis shows how the outcomes vary with the market and cost structure. (authors' abstract)Series: Department of Economics Working Paper Serie

Quality teaching matters: perspectives on quality teaching for the modernization of higher education. A position paper

This position paper attempts to ground the discussion on improving the quality of teaching in the context of Higher Education (HE) in order to take concrete directions toward what in the scientificliterature is identified as a culture of quality in education. This concept implies an approach to continuing monitoring, reflection and change toward innovation through main stakeholders’engagement. The paper will hence briefly introduce the policy context and research background at international and national level, in order to analyze the opportunities of implementinga culture of quality regarding teaching at the University of Trento. Furthermore, it will make a number of recommendations for the concrete implementation of the approach. The document is hence divided into the following parts:A first part, introducing the policy context regarding agenda for the modernization of HE in Europe and at international level. In this context, the issue of quality teaching is focused as key elementtowards better quality of Higher Education.A second part, regarding the importance and forms of innovation in pedagogical approaches in HIgher Education, as well as the conditions of professional development in academic staff regardingbetter teaching.A third part, consisting on the research carried out by our research unit within the University of Trento, regarding the issue of quality in Higher Education.A fourth part is devoted to introduce recommendations for the implementation of concrete measures and interventions at institutional level

Percolation in suspensions of polydisperse hard rods : quasi-universality and finite-size effects

We present a study of connectivity percolation in suspensions of hard spherocylinders by means of Monte Carlo simulation and connectedness percolation theory. We focus attention on polydispersity in the length, the diameter and the connectedness criterion, and invoke bimodal, Gaussian and Weibull distributions for these. The main finding from our simulations is that the percolation threshold shows quasi universal behaviour, i.e., to a good approximation it depends only on certain cumulants of the full size and connectivity distribution. Our connectedness percolation theory hinges on a Lee-Parsons type of closure recently put forward that improves upon the often-used second virial approximation [ArXiv e-prints, May 2015, 1505.07660]. The theory predicts exact universality. Theory and simulation agree quantitatively for aspect ratios in excess of 20, if we include the connectivity range in our definition of the aspect ratio of the particles. We further discuss the mechanism of cluster growth that, remarkably, differs between systems that are polydisperse in length and in width, and exhibits non-universal aspects.Comment: 7 figure

The impact of Universal Health Coverage on healthcare consumption and risky behaviours: evidence from Thailand

Thailand is among one of the first non OECD countries to have successfully introduced a form of Universal Health Coverage (UHC) in 2002. This policy defines a natural experiment for the evaluation of the effects of public health insurance on health behaviours. In the present paper, we look at the impact of the Thai UHC on preventive activities, risky behaviours and healthcare consumption using data from the 1996, 2001 and 2003 Health and Welfare Survey of Thailand. We use double robust estimators combining propensity scores and linear regressions to estimate Difference-in-Differences (DD) and Difference in DD (DDD) models. Results offer important insights. First, previously uninsured men and women increased their preventive activities (check-ups) more than any other groups. At the same time, there is no evidence of either an increase in risky behaviours or a reduction of preventive efforts by the newly insured population. In other words, we find no evidence of ex ante moral hazard. Regarding healthcare consumption, we see that hospital admissions increased by 2% and outpatient visits increased by 13% due to the UHC. Overall, these findings imply positive health impacts among the Thai population who entered in the UHC

Empowering girls, delaying marriage: Exploring the role of marital age and education on domestic violence in India

Domestic violence represents the most important component of violence against women. Whilst some literature report female empowerment as a protective factor against domestic violence, some literature find the opposite because the husband may attempt to compensate for the enhanced status of his wife. This paper aims to investigate the effects of female empowerment in the form of marital age and education on domestic violence in India, where intimate partner violence is amongst the highest in Asia. The analysis is based on the sample of eligible women aged 15-49 with valid response on domestic violence in the 2015- 2016 National Family Health Survey (NFHS-4) (n=9722). Upon estimating a series of instrumental variable (IV) regressions using age at menarche as an exogenous and strong instrument, we establish a causal relationship between empowerment and domestic violence taking into account the endogeneity of marital age and education. We further disentangle the relationships between domestic violence and age at marriage and education, separately. In addition, we investigate how maritage age and education influence domestic violence through labour market participation and spouse quality channels. We find that: i) empowered women do experience less domestic violence; ii) marital age and education are partially complementary; iii) labour market participation and spousal quality are relevant mediators of these relationships. Policies aiming at reducing domestic violence in India hence should be holistic, focussing on investing in education both for women and men and improving the conditions of the women’ labour market

Adaptation to poverty in long-run panel data

We consider the link between poverty and subjective well-being, and focus in particular on potential adaptation to poverty. We use panel data on almost 54,000 individuals living in Germany from 1985 to 2012 to show first that life satisfaction falls with both the incidence and intensity of contemporaneous poverty. We then reveal that there is little evidence of adaptation within a poverty spell: poverty starts bad and stays bad in terms of subjective well-being. We cannot identify any cause of poverty entry which explains the overall lack of poverty adaptation

Graves under the microscope: micromorphological study of sediments in archaeological burials

The InterArChive project investigated the sediment of the grave fills of archaeological burials. This study applied micromorphological analysis, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and image analysis on sediments of seventeen graves spanning from 4th C BC - 15th C AD and three experimental piglet burials (2009-2013). A new standardized and rapid method was developed for the measurement of porosity. The grave types comprised wooden coffin, absence of coffin and chamber tombs. The sediments were sandy clay soils, variably affected by water-logged conditions, from temperate oceanic climates; sandy loam soil and limestone and sandstone deposits in Mediterranean climates. The microstructure of the backfill, features produced by the decomposition of the corpse and interactions with the surrounding sediment, secondary products related to the environmental conditions in the grave, degree of weathering of bone fragments in the different contexts, preservation of organic components from the graves and biological activity during and after the corpse decomposition were investigated. The results showed that corpse decomposition within the soil produced characteristic microstructures and features according to the type of soil and climate. Neoformed minerals, such as vivianite, siderite and leucophosphite formed in water-logged soils and anaerobic conditions. Amorphous phosphates were preserved only in water-logged soils. In all environments examined redoximorphic pedofeatures formed in the area around the skeleton in the absence of a coffin or in the layers above the skeleton in the presence of a coffin. Organic components and bone fragments were rarely preserved, especially in limestone and sandstone deposits from warm climates. Fungal and mesofauna activities were better represented in aerobic conditions and Mediterranean climate. Changes in porosity and segregation of mineral grains showed downward movement of soil particles and fluids from the layers above the skeleton and they highlighted the role of the coffin as barrier to this movement

O fluxo de caixa descontado e o valor de mercado: o caso de uma indústria de máquinas e equipamentos localizada em Santa Catarina

Trabalho de Conclusão de Curso, apresentado para obtenção do grau de bacharel no curso de Ciências Contábeis da Universidade do Extremo Sul Catarinense, UNESC.A avaliação de empresas é fundamental para acompanhamento da geração de valor ou para um bem-sucedido processo de fusão ou aquisição. O objetivo geral desta pesquisa consiste em estimar o valor de uma empresa por meio do método de fluxo de caixa descontado. A pesquisa se caracteriza como descritiva, de abordagem qualitativa e desenvolvida por meio do estudo de caso e análise documental. A companhia escolhida para a pesquisa encontra-se listada no mercado de capitais e os dados foram coletados através de análise histórica de demonstrações contábeis. Assim, elaborou-se as premissas e projeções necessárias para o cálculo do valuation. Esta análise aplicou o método de fluxo de caixa descontado para encontrar o valor justo da companhia e através dos resultados conclui-se que a empresa está superavaliada, sugerindo que o preço justo das ações é inferior ao praticado pelo mercado na data da avaliação. Tal discrepância pode ser atribuída a um conjunto de fatores macroeconômicos que causaram volatilidade recente em preços de todos os ativos listados na B3