Influence de la précontrainte et de la température sur les propriétés électrique du VHB4910

International audienceLes élastomères diélectriques sont de plus en plus utilisés pour créer des transducteurs dans de nombreux domaines industriels : interface haptique, robotique, biomimétisme, énergie. Dans le domaine de l'énergie, le développement de générateurs électrostatiques souples tient une large place. Toutefois, le courant de fuite diminue l'efficacité et la durée de vie des dispositifs utilisant ces matériaux. Cette étude concerne donc l'influence des facteurs externes (étirement, température) sur les propriétés électriques du polyacrylate VHB4910, un des matériaux largement utilisés pour créer des générateurs. Nous relevons que le courant de fuite augmente avec l'augmentation de l'étirement. Ce comportement peut se combiner avec l'effet de la température

Synergistic Effect of Cloves (Syzygium aromaticum), Thyme (Thymus vulgaris) and Lemon (Citrus limon) Blended Essential Oils Optimized by Mixture Design for Improving the Antioxidant Activity

Background: Combining various essential oils (EOs) for developing pharmaceutical formulations has been the focus of attention in recent years. Objectives: This study aimed to determine the antioxidant effect of the combination of three Eos obtained from clove (Syzygium aromaticum L.), lemon peel (Citrus limon L.), and thyme (Thymus vulgaris L.) by using mixture design. Methods: The EOs of lemon peel (EOL), clove (EOC), and thyme (EOT) as well as their combination were analyzed using a gas chromatograph with flame ionization detector (GC/FID). The antioxidant activities of the EOs from EOL, EOC, and EOT as well as their combination were measured adopting DPPH assay. The construction and statistical analysis of the experiment were designed using the NemrodW (LPRAI, version 2000) software. Results: EOL, EOC, and EOT were found capable of neutralizing DPPH radical. EOC was distinguished by its strongest antiradical activity with IC50=15.02±0.02 µg/mL. EOT had an IC50=29.20±0.12 µg/mL while EOL had 188.69±0.95 µg/mL. The positive standard BHT was detected to be IC50=24±0.02 µg/ mL. The optimal, combinative mixture of essential oils may have been determined based on these isoresponse curves which allowed fixing the ideal combinations of ingredient in terms of quantity to obtain an EO mixture possessing appreciable and optimal antioxidant characteristics. The predicted antioxidant properties determined by the mixing plan model were retained and the experiments were carried out respecting the contents of proposed ingredients of 25.7% EOT, 32.3% EOL, and 41.9% EOC equivalent to 15.42 mg, 19.38 mg and 25.14 mg, respectively. This resulted in arriving at an essential oil mixture with an experimental IC50=11.023±0.145 µg/mL which was similar to those of the predicted antioxidant properties with an order of 10.907±0.212 µg/mL and a non-significant difference of P<0.05, based on which the validity of the proposed mixing plan model was determined. The combined EO was also found to be rich in eugenol (32.35±1.13%), thymol (25.49±0.03%), and limonene (21.30±0.02%). Conclusion: Statistical planning and the development of utility profiles for mixtures of essential oils may have been used to predict the optimal composition as well as to determine their antioxidant profile

Identification of candidate regions for a novel Usher syndrome type II locus

PURPOSE: Chronic diseases affecting the inner ear and the retina cause severe impairments to our communication systems. In more than half of the cases, Usher syndrome (USH) is the origin of these double defects. Patients with USH type II (USH2) have retinitis pigmentosa (RP) that develops during puberty, moderate to severe hearing impairment with downsloping pure-tone audiogram, and normal vestibular function. Four loci and three genes are known for USH2. In this study, we proposed to localize the gene responsible for USH2 in a consanguineous family of Tunisian origin. METHODS: Affected members underwent detailed ocular and audiologic characterization. One Tunisian family with USH2 and 45 healthy controls unrelated to the family were recruited. Two affected and six unaffected family members attended our study. DNA samples of eight family members were genotyped with polymorphic markers. Two-point and multipoint LOD scores were calculated using Genehunter software v2.1. Sequencing was used to investigate candidate genes. RESULTS: Haplotype analysis showed no significant linkage to any known USH gene or locus. A genome-wide screen, using microsatellite markers, was performed, allowing the identification of three homozygous regions in chromosomes 2, 4, and 15. We further confirmed and refined these three regions using microsatellite and single-nucleotide polymorphisms. With recessive mode of inheritance, the highest multipoint LOD score of 1.765 was identified for the candidate regions on chromosomes 4 and 15. The chromosome 15 locus is large (55 Mb), underscoring the limited number of meioses in the consanguineous pedigree. Moreover, the linked, homozygous chromosome 15q alleles, unlike those of the chromosome 2 and 4 loci, are infrequent in the local population. Thus, the data strongly suggest that the novel locus for USH2 is likely to reside on 15q. CONCLUSIONS: Our data provide a basis for the localization and the identification of a novel gene implicated in USH2, most likely localized on 15q

A comparative assessment of antifungal activity of essential oils of five medicinal plants from Tunisia

The leaf essential oil yields of clementine, cypress, rosemary, tea, and thyme were 0.22, 0.87, 1.46, 1.20, and 0.72%, respectively, based on the dry weight of the plant material. The leaf essential oils of rosemary, tea, and thyme contained the highest levels of oxygenated monoterpenes (60.14-91.70%). Rosemary and tea leaf essential oils were rich in 1,8-cineole (49.98% and 57.55%, respectively), and they have potent antifungal activity against Alternaria alternata strain (MIC = 5000 μg/ml). Thyme was rich in carvacrol (78.54%) and had a MIC of 6000 μg/ml against A. alternata strain. Clementine leaf essential oil was characterized by the predominance of monoterpene hydrocarbons (88.65%), and it possessed a weak antifungal activity against A. alternata (MIC = 8000 μg/ml). Cypress leaf essential oil was characterized by the predominance of oxygenated sesquiterpenes (60.67%), having an antifungal activity of 8000 μg/ml

A year of genomic surveillance reveals how the SARS-CoV-2 pandemic unfolded in Africa.

The progression of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic in Africa has so far been heterogeneous, and the full impact is not yet well understood. In this study, we describe the genomic epidemiology using a dataset of 8746 genomes from 33 African countries and two overseas territories. We show that the epidemics in most countries were initiated by importations predominantly from Europe, which diminished after the early introduction of international travel restrictions. As the pandemic progressed, ongoing transmission in many countries and increasing mobility led to the emergence and spread within the continent of many variants of concern and interest, such as B.1.351, B.1.525, A.23.1, and C.1.1. Although distorted by low sampling numbers and blind spots, the findings highlight that Africa must not be left behind in the global pandemic response, otherwise it could become a source for new variants

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Physical and electrical properties of electroactive polymers

Les élastomères diélectriques sont de plus en plus utilisés pour la réalisation des transducteurs dans de nombreux domaines industriels : interface haptique, robotique, biomimétisme, conversion d’énergie. Pour le fonctionnement de toutes ces applications, le polymère électroactif est soumis à une haute tension (de 1 à 10kV). Toutefois, le courant de fuite diminue l’efficacité et la durée de vie des dispositifs utilisant ces matériaux.Par ailleurs, une précontrainte mécanique (étirement) est généralement appliquée au polymère pour accroître l’efficacité énergétique dans la conversion mécanique-électrique. Les courants de fuite (et donc le champ de claquage du polymère) seront ainsi conditionnés par cette précontrainte et ce point doit faire l’objet d’une étude détaillée.L’objet de ce travail de thèse est de mener des analyses de courant de fuite sur des polymères électroactifs (élastomères polyacrylates du commerce VHB4910 et silicones Sylgard 186) non contraints et contraints mécaniquement pour évaluer l’amélioration ou la dégradation des performances électriques lorsqu’ils seront plus tard intégrés en géométrie électrode-polymère-électrode dans des transducteurs.Tout d’abord, nous avons mené une étude exhaustive sur l’influence des facteurs externes (étirement, température, champ électrique, nature de l’électrode) sur les propriétés électriques du polyacrylate VHB4910. Les études ont été réalisés sur des durées de polarisation courtes (quelques minutes) et longues (jusqu’à 15 heures). Au cours de ce travail, nous sommes également intéressés à l’étude du phénomène d’autocicatrisation sur le sylgard 186. Les tests ont été conduits pour différents types d’électrodes (or, aluminium, graphène, nanoplaquettes de graphène : GnP) déposées sur la surface de silicone. Une analyse par microscopie optique de la zone évaporée a été menée.La finalité de ces travaux aura permis d’optimiser des structures de récupération d’énergie électrostatique à base de polymères électroactifs.Electroactive polymers known as dielectric elastomers have shown considerable promise for transducers. They are attractive for a wide range of innovative applications including softs robots, adaptive optics, haptic interface or biomedical actuation thanks to their high energy density and good efficiency. For the functioning of all these application, the electroactive polymer is subjected to high electrical field. Nevertheless, the performances of these transducers are affected by the losses and especially the ones induced by the leakage current.Mechanical pre-stretch is an effective method to improve actuation when a voltage is applied to the device made up of a dielectric elastomer sandwiched between two compliant electrodes. The overall performances of the structure (electromechanical conversion, efficiency, strain induced…) depend strongly on the electric and mechanical properties of the elastomer. Regarding electric characteristics, dielectric permittivity, dissipation factor and electric breakdown field have been deeply investigated according to various parameters such as frequency, temperature, pre-stretch, or nature of the electrodes but complete analysis of the leakage current is missing in the scientific literature.Thus, this work reports an extensive investigation on the stability of the current-time characteristics in dielectric elastomer. Particularly, we focus on the influence of the nature of the electrodes and pre-stress applied to the transducer. In order to evaluate the influence of the time duration on the behavior of the leakage current, short and long-term electrical stress times was applied during short times and up to 15 hours.Leakage current in electroactive polymers were discussed for a commercial polyacrylate (VHB4910 from 3M) currently used for soft transducers applications. This current is investigated as a function of external factors (stretching, temperature, type of material for electrodes)In order to evaluate the limitations in term of voltage and in the goal to increase the lifetime of these transducers, the second part of our study is focused on the dielectric strength of silicone rubbers for various types of electrodes (gold, Aluminum, graphene nanoplatelets, graphene : GnP). The effect of self-healing is particularly studied and a selection of electrodes for soft transducers based on dielectric elastomers is proposed

Propriétés physiques et électriques de polymères électroactifs

Electroactive polymers known as dielectric elastomers have shown considerable promise for transducers. They are attractive for a wide range of innovative applications including softs robots, adaptive optics, haptic interface or biomedical actuation thanks to their high energy density and good efficiency. For the functioning of all these application, the electroactive polymer is subjected to high electrical field. Nevertheless, the performances of these transducers are affected by the losses and especially the ones induced by the leakage current.Mechanical pre-stretch is an effective method to improve actuation when a voltage is applied to the device made up of a dielectric elastomer sandwiched between two compliant electrodes. The overall performances of the structure (electromechanical conversion, efficiency, strain induced…) depend strongly on the electric and mechanical properties of the elastomer. Regarding electric characteristics, dielectric permittivity, dissipation factor and electric breakdown field have been deeply investigated according to various parameters such as frequency, temperature, pre-stretch, or nature of the electrodes but complete analysis of the leakage current is missing in the scientific literature.Thus, this work reports an extensive investigation on the stability of the current-time characteristics in dielectric elastomer. Particularly, we focus on the influence of the nature of the electrodes and pre-stress applied to the transducer. In order to evaluate the influence of the time duration on the behavior of the leakage current, short and long-term electrical stress times was applied during short times and up to 15 hours.Leakage current in electroactive polymers were discussed for a commercial polyacrylate (VHB4910 from 3M) currently used for soft transducers applications. This current is investigated as a function of external factors (stretching, temperature, type of material for electrodes)In order to evaluate the limitations in term of voltage and in the goal to increase the lifetime of these transducers, the second part of our study is focused on the dielectric strength of silicone rubbers for various types of electrodes (gold, Aluminum, graphene nanoplatelets, graphene : GnP). The effect of self-healing is particularly studied and a selection of electrodes for soft transducers based on dielectric elastomers is proposed.Les élastomères diélectriques sont de plus en plus utilisés pour la réalisation des transducteurs dans de nombreux domaines industriels : interface haptique, robotique, biomimétisme, conversion d’énergie. Pour le fonctionnement de toutes ces applications, le polymère électroactif est soumis à une haute tension (de 1 à 10kV). Toutefois, le courant de fuite diminue l’efficacité et la durée de vie des dispositifs utilisant ces matériaux.Par ailleurs, une précontrainte mécanique (étirement) est généralement appliquée au polymère pour accroître l’efficacité énergétique dans la conversion mécanique-électrique. Les courants de fuite (et donc le champ de claquage du polymère) seront ainsi conditionnés par cette précontrainte et ce point doit faire l’objet d’une étude détaillée.L’objet de ce travail de thèse est de mener des analyses de courant de fuite sur des polymères électroactifs (élastomères polyacrylates du commerce VHB4910 et silicones Sylgard 186) non contraints et contraints mécaniquement pour évaluer l’amélioration ou la dégradation des performances électriques lorsqu’ils seront plus tard intégrés en géométrie électrode-polymère-électrode dans des transducteurs.Tout d’abord, nous avons mené une étude exhaustive sur l’influence des facteurs externes (étirement, température, champ électrique, nature de l’électrode) sur les propriétés électriques du polyacrylate VHB4910. Les études ont été réalisés sur des durées de polarisation courtes (quelques minutes) et longues (jusqu’à 15 heures). Au cours de ce travail, nous sommes également intéressés à l’étude du phénomène d’autocicatrisation sur le sylgard 186. Les tests ont été conduits pour différents types d’électrodes (or, aluminium, graphène, nanoplaquettes de graphène : GnP) déposées sur la surface de silicone. Une analyse par microscopie optique de la zone évaporée a été menée.La finalité de ces travaux aura permis d’optimiser des structures de récupération d’énergie électrostatique à base de polymères électroactifs

Electrical conduction in dielectric elastomer transducers

WOS:000516579400003Dielectric elastomers are considered to be promising materials for applications in energy harvesting, haptic interface or biomedical actuation, thanks to their high energy density and attractive efficiency. Nevertheless, the performance of dielectric elastomer transducers (DETs) are affected by losses, especially losses induced by leakage current. This work reports an extensive investigation into the stability of the current-time characteristics of VHB4910 dielectric elastomers, currently in use for such applications. It should be noted that conductive pastes that act as compliant electrodes play an important role in the behavior of the current. The Schottky current is thus disturbed at the electrode - elastomer interface and an increase in current is observed over time when the device is subjected to electrical voltages over long periods of time. Pre-stress, commonly applied for application using VHB4910, influences also significantly the electrical response. Thus, for a same stretching of the material, asymmetric stretching is preferred over symmetric stretching in order to obtain a lower leakage current. This difference in behavior is explained by the fact that the polymer chains are stretched in preferential directions which will then lead to specific responses of both the dipoles and other conduction mechanisms such as hopping. Finally, a simple analytical model is proposed to report the current behavior in these materials according to the nature of the electrodes and the pre-stretching applied