On the Linear Viscoelastic Behavior of Polyolefins in the Molten State: Influence of Long Chain Branching

This contribution presents a survey on the influence of long chain branching on the linear viscoelastic properties. The aim of this article is to provide evidence that rheological testing is a potent tool for characterising polymers in the melts. The materials chosen are linear and slightly long- chain branched metallocene- catalysed polyethylene of narrow molecular mass distribution, as well as linear and highly long- chain branched polyethylene of broad molecular mass distribution, and other sample of the big family of polyolefin’s. The linear viscoelastic flow properties are determined in shear creep and recovery experiments by means of a magnetic bearing torsional creep apparatus. The interest of this study consists in reviewing various experimental, theoretical and simulation results of the some viscoelastic properties. The samples with a slight degree of long- chain branching exhibit a surprisingly high zero shear-rate viscosity in comparison to linear one, whereas the highly branched polymers have a much lower viscosity compared to linear samples. Slightly branched polyethylene have got a higher steady- state compliance in comparison to linear products of similar polydispersity, whereas the highly branched polyethylene of broad molecular mass distribution exhibit a surprisingly low elasticity in comparison to linear broad molecular one. The same remarks are obtained for the other samples. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the main polymer chain are the principal factors that control the material rheology.This contribution presents a survey on the influence of long chain branching on the linear viscoelastic properties. The aim of this article is to provide evidence that rheological testing is a potent tool for characterising polymers in the melts. The materials chosen are linear and slightly long- chain branched metallocene- catalysed polyethylene of narrow molecular mass distribution, as well as linear and highly long- chain branched polyethylene of broad molecular mass distribution, and other sample of the big family of polyolefin’s. The linear viscoelastic flow properties are determined in shear creep and recovery experiments by means of a magnetic bearing torsional creep apparatus. The interest of this study consists in reviewing various experimental, theoretical and simulation results of the some viscoelastic properties. The samples with a slight degree of long- chain branching exhibit a surprisingly high zero shear-rate viscosity in comparison to linear one, whereas the highly branched polymers have a much lower viscosity compared to linear samples. Slightly branched polyethylene have got a higher steady- state compliance in comparison to linear products of similar polydispersity, whereas the highly branched polyethylene of broad molecular mass distribution exhibit a surprisingly low elasticity in comparison to linear broad molecular one. The same remarks are obtained for the other samples. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the main polymer chain are the principal factors that control the material rheology

Dissociated Representations of Pleasant and Unpleasant Olfacto-Trigeminal Mixtures: An fMRI Study

How the pleasantness of chemosensory stimuli such as odorants or intranasal trigeminal compounds is processed in the human brain has been the focus of considerable recent interest. Yet, so far, only the unimodal form of this hedonic processing has been explored, and not its bimodal form during crossmodal integration of olfactory and trigeminal stimuli. The main purpose of the present study was to investigate this question. To this end, functional magnetic resonance imaging (fMRI) was used in an experiment comparing brain activation related to a pleasant and a relatively unpleasant olfacto-trigeminal mixture, and to their individual components (CO2 alone, Orange alone, Rose alone). Results revealed first common neural activity patterns in response to both mixtures in a number of regions: notably the superior temporal gyrus and the caudate nucleus. Common activations were also observed in the insula, although the pleasant mixture activated the right insula whereas the unpleasant mixture activated the left insula. However, specific activations were observed in anterior cingulate gyrus and the ventral tegmental area only during the perception of the pleasant mixture. These findings emphasized for the firs time the involvement of the latter structures in processing of pleasantness during crossmodal integration of chemosensory stimuli

PROPRIETES STRUCTURALES DE COPOLYMERES BISEQUENCE ET TRISEQUENCE LINEAIRES ET DE LEUR HOMOLOGUE CYCLIQUE EN SOLUTION DILUEE STRUCTURAL PROPERTIES OF LINEAR DIBLOCK AND TRIBLOCK COPOLYMERS AND THEIR CYCLIC HOMOLOGOUS IN DILUTE SOLUTION

SUMMARYThe structural properties of linear block copolymers in solution aroused a considerable interest and are the subject of manytheoretical and experimental investigations. However, their cyclic counterparts received only a limited attention fromresearchers mainly because of difficulties related to their synthesis with high-molecular weights and a low polydispersity. Thisstudy was justified by the relatively recent light scattering measurements carried out by Amis et al. on a cyclic diblockcopolymer and its linear triblock counterpart made up of polystyrene (PS) and poly(dimethylsiloxane) (PDMS). In this work,the adopted theoretical approach is based on the random phase approximation when the polymeric systems under study areplaced in similar conditions of temperature, concentration, composition and mass than those covered experimentally by Amisand others. The main objective of this study is intended to present a theoretical formalism allowing a systematic analysis of thescattering data, relating to block copolymers of arbitrary architectures, and to suggest some indications relating to theirtreatment. In terms of thermodynamic and structural properties, the results obtained reveal differences between the two typesof copolymers. In particular, contrary to what was brought back by Amis and his collaborators, the discrepancies, shownbetween the radii of gyration of linear block copolymers and their cyclic counterpart, being sufficiently large, it should bepossible to highlight them in experiments by light scattering.RESUMELes propriétés structurales de copolymères séquencés linéaires en solution ont suscité un intérêt considérable et fait l'objet denombreuses investigations théoriques et expérimentales. Cependant, leurs homologues cycliques n'ont retenu l'attention qued'un nombre limité de chercheurs principalement du fait de difficultés liées à leur synthèse avec des poids moléculaires élevéset une faible polydispersité. Cette étude a été motivée par des mesures de diffusion de lumière relativement récentes réaliséespar Amis et al. sur un copolymère biséquencé cyclique et son homologue triséquencé linéaire constitué de polystyrène (PS) etde poly(diméthylsiloxane) (PDMS). Dans ce travail, l'approche théorique adoptée est basée sur l'approximation de la phasealéatoire en plaçant les systèmes polymériques considérés dans des conditions de température, de concentration, decomposition et de masse similaires à celles couvertes expérimentalement par Amis et autres. L’objectif premier de la présenteétude consiste à présenter un formalisme théorique permettant une analyse systématique de données de diffusion, relatives àdes copolymères séquencés d'architectures arbitraires, et de suggérer quelques indications concernant le traitement de celles-ci.En termes de propriétés thermodynamiques et structurales, les résultats obtenus révèlent des écarts entre les deux types decopolymères. En particulier, contrairement à ce qui a été rapporté par Amis et ses collaborateurs, les différences, relevées entreles rayons de giration de copolymères séquencés linéaires et de leur homologue cyclique, étant suffisamment importantes, ildevrait être possible de les mettre en évidence expérimentalement par diffusion de lumière

Assessing Implicit Odor Localization in Humans Using a Cross-Modal Spatial Cueing Paradigm

Navigation based on chemosensory information is one of the most important skills in the animal kingdom. Studies on odor localization suggest that humans have lost this ability. However, the experimental approaches used so far were limited to explicit judgements, which might ignore a residual ability for directional smelling on an implicit level without conscious appraisal.A novel cueing paradigm was developed in order to determine whether an implicit ability for directional smelling exists. Participants performed a visual two-alternative forced choice task in which the target was preceded either by a side-congruent or a side-incongruent olfactory spatial cue. An explicit odor localization task was implemented in a second experiment.No effect of cue congruency on mean reaction times could be found. However, a time by condition interaction emerged, with significantly slower responses to congruently compared to incongruently cued targets at the beginning of the experiment. This cueing effect gradually disappeared throughout the course of the experiment. In addition, participants performed at chance level in the explicit odor localization task, thus confirming the results of previous research.The implicit cueing task suggests the existence of spatial information processing in the olfactory system. Response slowing after a side-congruent olfactory cue is interpreted as a cross-modal attentional interference effect. In addition, habituation might have led to a gradual disappearance of the cueing effect. It is concluded that under immobile conditions with passive monorhinal stimulation, humans are unable to explicitly determine the location of a pure odorant. Implicitly, however, odor localization seems to exert an influence on human behaviour. To our knowledge, these data are the first to show implicit effects of odor localization on overt human behaviour and thus support the hypothesis of residual directional smelling in humans

ON THE STATIC AND DYNAMIC SCATTERING FROM LINEAR AND BRANCHED POLYELECTROLYTES AT VARIOUS SCREENING LENGTHS PROPRIETES DE DIFFUSION STATIQUE ET DYNAMIQUE DE POLYELECTROLYTES LINEAIRES ET RAMIFIES A DIVERSES LONGUEURS D’ECRAN

During the two last decades, branched polyelectrolytes have been thoroughly studied from theoretical and experimentalstandpoints. In this report, we attempt to compare the behaviour of highly branched polyelectrolytes to that of their linearcounterparts at low ionic strength. As expected, the expansion behaviour of the branched materials is considerably less than ofthat of the corresponding linear chains. Surprisingly, in the former case (sphere-like behavior), the ratio of the radius ofgyration to the hydrodynamic radius ρ=Rg/Rh shows an opposite behaviour as compared to the second one (rod-like behavior);indeed, contrary to the case of linear chains for which this ratio increases, that of branched homologous decreases as the ionicstrength is lowered. Analyzis of the data, depicted in Kratky plots, reveals substantial discrepancies between the bothpolymeric structures. Moreover, at high ionic strength, one observes a rod-like structure that undergoes a transition to adisordered conformation which is not however that of a random coil, whereas, at low one, it appears that the two double- helixunfold and the loop strongly expands. Ces deux dernières décennies, les polyélectrolytes ramifiés ont été activement étudiés sur le double plan théorique etexpérimental; le propos de cette étude est de tenter de comparer le comportement de polyélectrolytes fortement ramifiés à celuide leurs homologues linéaires pour des forces ioniques faibles. Comme attendu, l'expansion des matériaux ramifiés estconsidérablement moindre que celle des chaînes linéaires correspondantes. Cependant, il est surprenant que, dans le premiercas (comportement d’une sphère), le rapport du rayon de giration au rayon hydrodynamique ρ =Rg/Rh montre uncomportement opposé à celui correspondant au second cas (comportement de bâtonnet); en effet, contrairement au cas deschaînes linéaires pour lesquelles ce rapport croît, celui de leurs homologues ramifiés diminue à mesure que la concentrationionique est abaissée. L’analyse des données, mises en évidence dans la représentation de Kratky, indique des écartssubstantiels entre les deux structures polymériques. Par ailleurs, pour une force ionique élevée, on observe une structure enforme de bâtonnet qui subit une transition vers une conformation désordonnée qui n'est cependant pas celle d’une pelotestatistique, tandis que, pour des forces ioniques basses, il apparaît que les deux double-hélices ne se replient pas et la boucles’étend fortement

Semantic Knowledge Influences Prewired Hedonic Responses to Odors

Background Odor hedonic perception relies on decoding the physicochemical properties of odorant molecules and can be influenced in humans by semantic knowledge. The effect of semantic knowledge on such prewired hedonic processing over the life span has remained unclear. Methodology/Principal Findings The present study measured hedonic response to odors in different age groups (children, teenagers, young adults, and seniors) and found that children and seniors, two age groups characterized by either low level of (children) or weak access to (seniors) odor semantic knowledge, processed odor hedonics more on the basis of their physicochemical properties. In contrast, in teenagers and young adults, who show better levels of semantic odor representation, the role of physicochemical properties was less marked. Conclusions/Significance These findings demonstrate for the first time that the biological determinants that make an odor pleasant or unpleasant are more powerful at either end of the life span

Past, Present, and Future of Human Chemical Communication Research

Although chemical signaling is an essential mode of communication in most vertebrates, it has long been viewed as having negligible effects in humans. However, a growing body of evidence shows that the sense of smell affects human behavior in social contexts ranging from affiliation and parenting to disease avoidance and social threat. This article aims to (a) introduce research on human chemical communication in the historical context of the behavioral sciences; (b) provide a balanced overview of recent advances that describe individual differences in the emission of semiochemicals and the neural mechanisms underpinning their perception, that together demonstrate communicative function; and (c) propose directions for future research toward unraveling the molecular principles involved and understanding the variability in the generation, transmission, and reception of chemical signals in increasingly ecologically valid conditions. Achieving these goals will enable us to address some important societal challenges but are within reach only with the aid of genuinely interdisciplinary approaches

An olfactory self-test effectively screens for COVID-19

International audienceAbstract Background Key to curtailing the COVID-19 pandemic are wide-scale screening strategies. An ideal screen is one that would not rely on transporting, distributing, and collecting physical specimens. Given the olfactory impairment associated with COVID-19, we developed a perceptual measure of olfaction that relies on smelling household odorants and rating them online. Methods Each participant was instructed to select 5 household items, and rate their perceived odor pleasantness and intensity using an online visual analogue scale. We used this data to assign an olfactory perceptual fingerprint, a value that reflects the perceived difference between odorants. We tested the performance of this real-time tool in a total of 13,484 participants (462 COVID-19 positive) from 134 countries who provided 178,820 perceptual ratings of 60 different household odorants. Results We observe that olfactory ratings are indicative of COVID-19 status in a country, significantly correlating with national infection rates over time. More importantly, we observe indicative power at the individual level (79% sensitivity and 87% specificity). Critically, this olfactory screen remains effective in participants with COVID-19 but without symptoms, and in participants with symptoms but without COVID-19. Conclusions The current odorant-based olfactory screen adds a component to online symptom-checkers, to potentially provide an added first line of defense that can help fight disease progression at the population level. The data derived from this tool may allow better understanding of the link between COVID-19 and olfaction

Subliminally Perceived Odours Modulate Female Intrasexual Competition: An Eye Movement Study

Background: Evidence suggests that subliminal odorants influence human perception and behavior. It has been hypothesized that the human sex-steroid derived compound 4,16-androstadien-3-one (androstadienone) functions as a human chemosignal. The most intensively studied steroid compound, androstadienone is known to be biologically relevant since it seems to convey information about male mate quality to women. It is unclear if the effects of androstadienone are menstrual cycle related. Methodology/Principal Findings: In the first experiment, heterosexual women were exposed to androstadienone or a control compound and asked to view stimuli such as female faces, male faces and familiar objects while their eye movements were recorded. In the second experiment the same women were asked to rate the level of stimuli attractiveness following exposure to the study or control compound. The results indicated that women at high conception risk spent more time viewing the female than the male faces regardless of the compound administered. Women at a low conception risk exhibited a preference for female faces only following exposure to androstadienone. Conclusions/Significance: We contend that a woman’s level of fertility influences her evaluation of potential competitors (e.g., faces of other women) during times critical for reproduction. Subliminally perceived odorants, such as androstadienone, might similarly enhance intrasexual competition strategies in women during fertility phases not critica