Structure property relationships in electron donating systems for potential photovoltaic applications.

Conjugated polymers are considered to be one-dimensional semiconductors. In conjugated polymers single and double bonds alternatively bond the carbon atoms along the polymer chain. The loosely bound electrons determine the electronic properties of conjugated polymers. In order to utilise the properties of conjugated polymers in terms of a photovoltaic (PV) device application an acceptor material must be added. The acceptor material used in this study is used in buckminsterfullerence (C60). C60 was selected for this purpose due to its size and the fact that it can accept up to six additional electrons. Ultrafast charge transfers from a conducting polymer onto C60 were first reported in 1992 by Sariciftci et al. in a blend of MEH-PPV (poly (2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene) and since then it’s properties as an electron acceptor have been widely investigated. The debate of the exact mechanism of the charge transfer in polymer/fullerence blends is still on going today. The investigation of these systems is predominantly done using time resolved spectroscopy (photoinducted absorption, PIA), which is still considered to be the most effective way of investigation charge transfer between polymer/fullerence composites. However time resolved spectroscopy is expensive and is not readily available for use. The aim of this study is to explore charge transfer signatures in polymer/fullerence composites without using PIA spectroscopy. This study proposes to use steady state spectroscopic techniques coupled with electrochemical and conductivity measurements to characterise charge transfer signatures in polymer fullerence composites. The much studied MEH-PPV/C60 model system was initially employed in a systematic approach to try and elucidate charge transfer indicators between the polymers and C60 Fluorescence spectroscopy, cyclic volammetry, spectroelectrochemical and conductivity measurements provided evidence of charge transfer signatures in the model composite and were seen to be potentially viable techniques for assessing novel systems. The study was then extended to a homologous series of polymers which have continuously varying electronic and optical properties. The polymer series was synthesised in house and characterised for the first time in the solid state as part of this work. Electronic spectroscopy of the polymer series revealed that aggregation was recurring in the solid state form of the polymers. The electronic properties of the molecular and solid-state forms are different and the structure property relationships previously determined for the molecular forms could not be applied to the solid-state. It was observed that emission spectra of the polymers were all seen to be red shifted compared to those of their isolated molecular form. The fluorescence yield was also low, which also confirmed that there are aggregates within the polymers in their solid-state form. Cyclic volammetry measurements allowed calculation of the exact positioning of the HOMO-LUMO levels of each polymer. The precise levels of the HOMO-LUMO levels are important when matching the energy levels of the polymer to the energy levels of C60. Electrochemical bandgaps were in close accordance to the optical bandgaps. In-situ spectroelectrochemical measurements allowed observations of the bipolaron energy states of each polymer. Electroabsorption studies showed that each polymer was dominated by the quadratic Stark effect. The electroabsorption spectrum of each polymer closely resembled a first derivative lineshape of it’s absorption spectrum indicating a dominance of intramolecular transitions within each of the polymers. Using two of the new polymers a synthetic probe of the charge transfer mechanism was obtained. Charge transfer markers were evident in the new composites using fluorescence spectroscopy, cyclic volammetry, spectroelectrochemical measurements and conductivity measurements. For the results it was seen that the interaction of the two polymers with the C60 varied. From this systematic approach it was possible to observe which of the polymers showed the most potential for a device application by matching of the appropriate energy levels to achieve a more efficient charge transfer. In general it can be said that using a approach it was possible to match up the energy levels of a polymer/fullerence composite in order to achieve a more efficient interaction, which can be measured without the need for time resolved spectroscopy

Temperature dependence of indentation size effects, pile-up and strain rate sensitivity in polycrystalline tungsten from 25-950 C

Elevated temperature nanoindentation measurements were performed on polycrystalline tungsten to 950 ºC. Tests were carried out under high vacuum conditions as tungsten oxidizes in air at \u3e500 ºC. The temperature dependence of the hardness, elastic modulus, strain rate sensitivity, activation volume and the indentation size effect in hardness were investigated at 25, 750, 800, 850, 900 and 950 ºC. Thermal drift assessed from the last 60% of a hold period at 90% unloading was typically ~0.05 nm/s and it did not vary significantly with load or temperature [1]. The hardness measurements were in good agreement with previous determinations by non-depth sensing hot microhardness. Please click Additional Files below to see the full abstract

Linear Electronic and Optical Processes in Fullerene Thin Films

The electrical properties of C60 have been extensively studied in both the solid and solution phases. The vibrational spectroscopy of C60 is predominantly molecular in character. However electronic spectroscopy reveals features, which are specific to the solid. These features have been attributed to intermolecular charge transfer states. The relative importance of these inter – and intramolecular processes in terms of their contribution to the electronic transport is discussed. Cyclic voltammetry is employed to generate charged molecular species, which also contribute to the conduction process and comparisons to optical excited states species are drawn. The cyclic voltammetry was monitored in situ with vibrational spectroscopy so as to observe any shifts in the C60 spectrum due to charging. The current voltage characteristics of thin film sandwich structures fabricated by vacuum are then presented and discussed. A strongly non-linear behaviour is observed, a sharp increase in the device conductance being observed at relatively low voltages at both room temperature and at 20K. The room temperature IV curves confirm a lattice collapse upon charging. The high conductivity state is however observed to be stable at low temperature

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Correction to: Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

The original version of this article unfortunately contained a mistake

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Electrochemical Characterisation of Poly Arylene Vinylenes

The electrochemical properties of a newly synthesised set of PPV derivatives were measured by cyclic voltammetry. A new octyloxy substituted PPV derivative was first synthesised (POPV). The structure of the POPV is varied systematically by the replacement of the phenyl units by naphthyl and anthryl units and the effect of these variations on the electrochemical properties is explored. The HOMO–LOMO levels of the polymers were determined from the onset potentials for the p-doping and n-doping scans. From this the electrochemical bandgap for each of the polymers was calculated. The systematic change in the structure of the POPV results in a systematic increase in the LOMO level of the polymer series whereas a concomitant increase in HOMO level results in an overall increase in the bandgap of the polymers series. The variation in the electrochemical, optical properties and vibrational properties observed within the polymer series were all found to correlate with the structural changes made, pointing towards structure property relationships and a guide to future synthetic strategies

Interaction of Carbon Nanotubes with Saccharides: a Possible Route to Biocompatible Composites

Inclusion complexes of saccharides and HiPco Carbon Nanotubes (HCNT) were formed, resulting in water soluble complexes. These complexes were then characterised using a variety of spectroscopic techniques. Raman spectroscopy was used to probe changes in the vibrational character of both the host and guest species and also to assess if any selectivity of tube diameter occurred. UV-Vis-NIR and circular dichroic spectroscopies were used to assess the effect of inclusion on the electronic properties of the tubes. Spectroscopic analysis of these species showed clear evidence of an intermolecular interaction between the host material and the HCNT

New routes to functionalize carbon black for polypropylene nanocomposites

Methods for chemical surface functionalization for carbon black (CB) nanoparticles were studied to produce (CB)/polypropylene (PP) nanocomposites with superior electrical and thermal properties. Nanoparticle dispersion is known to directly control the extent to which nanocomposites maximize the unique attributes of their nanoscale fillers. As a result, tailored nanoparticle surface chemistry is a widely utilized method to enhance the interfacial interactions between nanoparticles and polymer matrices, assisting improved filler dispersion. In this work, a rapid chemical functionalization approach using a number of diarylcarbene derivatives, followed by the azo-coupling of substituted diazonium salts, for the covalent introduction of selected functional groups to the CB surface, is reported. Characterization of the modified CB by XPS, TGA, CHN, and ATR-IR collectively confirmed surface functionalization, estimating surface grafting densities of the order of 1013 and 1014 molecules/cm2. Nanocomposites, synthesized by solvent mixing PP with pristine and modified CB, demonstrated macroscopic property changes as a result of the nanoparticle surface functionalization. Pronounced improvements were observed for PP nanocomposites prepared with a dodecyl-terminated diaryl functionalized CB, in which TEM analysis established improved nanofiller dispersion owing to the enhanced CB-PP interfacial interactions in the nanocomposite. Observed dielectric relaxation responses at 20 wt % loading and a reduced percolation threshold realized conductivities of 1.19 × 10–4 S cm–1 at 10 wt %, compared to 2.62 × 10–15 S cm–1 for pristine CB/PP nanocomposites at the same filler loading. In addition, thermal properties signify an increase in the number of nucleation sites by the raised degree of crystallinity as well as increased melting and crystallization temperatures

Growth and Characterization of Strained and Alloyed Type-II ZnTe/ZnSe Core-Shell Nanocrystals

We investigate the growth and the physical and optical properties of type-II heterostructured ZnTe/ZnSe colloidal nanocrystals, focusing on the role of the 7% lattice mismatch between the two materials in determining growth homogeneity and band structure. We find that the lattice mismatch between the two materials places limitations on the range of structures that can be grown, and for those in which coherent growth is achieved we present clear evidence that the low bulk modulus ZnTe cores are compressed by the higher modulus ZnSe shells, accentuating the red-shift of the excitonic state with increasing shell thickness. By employing a variety of characterization tools we build a clear picture of the core-shell architecture. We show how strain is manifested in structures with sharp core-shell interfaces and how intentional alloying of the interface can influence the growth and exciton energies. We show that a (2,6)-band effective mass model is able to distinguish between the as-grown "sharp" and "alloyed" interfaces, indicating that the alloyed structures incorporate reduced strain