Mechanochromic effects in structurally colored materials are the result of deformation‐induced changes to their ordered nanostructures. Polymeric materials which respond in this way to deformation ...offer an attractive combination of characteristics, including continuous strain sensing, high strain resolution, and a wide strain‐sensing range. Such materials are potentially useful for a wide range of applications, which extend from pressure‐sensing bandages to anti‐counterfeiting devices. Focusing on the materials design aspects, recent developments in this field are summarized. The article starts with an overview of different approaches to achieve mechanochromic effects in structurally colored materials, before the physical principles governing the interaction of light with each of these materials types are summarized. Diverse methodologies to prepare these polymers are then discussed in detail, and where applicable, naturally occurring materials that inspired the design of artificial systems are discussed. The capabilities and limitations of structurally colored materials in reporting and visualizing mechanical deformation are examined from a general standpoint and also in more specific technological contexts. To conclude, current trends in the field are highlighted and possible future opportunities are identified.
Mechanochromic effects in structurally colored polymeric materials are the result of deformation‐induced changes to their ordered nanostructures. These are of great interest for technological applications, such as pressure‐sensing bandages, anti‐counterfeiting devices, and for fundamental research on the mechanical failure of polymeric materials. The synthetic approaches toward these materials are summarized, and a critical analysis of their mechanosensing capabilities is provided.
Sleep duration changes across the life course and differs by education in the United States. However, little research has examined whether educational differences in sleep duration change over age—or ...whether sleep duration trajectories over age differ by education. This study uses a life course approach to analyze American Time Use Survey data (N = 60,908), examining how educational differences in weekday sleep duration change from middle to older adulthood (ages 40–79). For men only, differences in total sleep time between individuals with less than a high school degree and those with more education converge in older adulthood. Results suggest that this leveling is explained by decreasing educational stratification in work hours as men enter older adulthood. Findings highlight the importance of employment for shaping gendered socioeconomic differences in sleep and demonstrate differences by education in how sleep duration changes over age, with possible implications for health disparities.
This investigation tested the effect of priming on pareidolia (the hearing of illusory words in ambiguous stimuli). Participants (41 women, 20 men, mean age 29.95 years) were assigned to primed (n = ...30) or unprimed (n = 31) groups: the former were told the study was of ‘purported ghosts voices’, the latter ‘voices in noisy environments.’ Participants were assessed for perception of human voices within recordings of purported electronic voice phenomena (EVP), degraded human speech, normal human speech, and white noise. The primed group had significantly higher perception of voices within EVPs than in degraded speech, this difference was not found for unprimed participants. In contrast to the previous use of this design, the primed group did not have higher perception of voices in EVPs and degraded speech than did the unprimed group. The Aesthetic Sensitivity dimension of the Highly Sensitive Person Scale (HSPS) was associated with detection of degraded stimuli, but not with accuracy of stimulus identification. HSPS score was related to lifetime reporting of anomalous and paranormal experiences. This study partially replicates a paranormal priming effect and shows relationships between HSPS and detection of ambiguous stimuli and anomalous and paranormal experiences.
Mechanics of elastomeric molecular composites Millereau, Pierre; Ducrot, Etienne; Clough, Jess M. ...
Proceedings of the National Academy of Sciences - PNAS,
09/2018, Letnik:
115, Številka:
37
Journal Article
Recenzirano
Odprti dostop
A classic paradigm of soft and extensible polymer materials is the difficulty of combining reversible elasticity with high fracture toughness, in particular for moduli above 1 MPa. Our recent ...discovery of multiple network acrylic elastomers opened a pathway to obtain precisely such a combination. We show here that they can be seen as true molecular composites with a well–cross-linked network acting as a percolating filler embedded in an extensible matrix, so that the stress–strain curves of a family of molecular composite materials made with different volume fractions of the same cross-linked network can be renormalized into a master curve. For low volume fractions (<3%) of cross-linked network, we demonstrate with mechanoluminescence experiments that the elastomer undergoes a strong localized softening due to scission of covalent bonds followed by a stable necking process, a phenomenon never observed before in elastomers. The quantification of the emitted luminescence shows that the damage in the material occurs in two steps, with a first step where random bond breakage occurs in the material accompanied by a moderate level of dissipated energy and a second step where a moderate level of more localized bond scission leads to a much larger level of dissipated energy. This combined use of mechanical macroscopic testing and molecular bond scission data provides unprecedented insight on how tough soft materials can damage and fail.
Strain‐induced light emission from mechanoluminescent cross‐linkers in silica‐filled poly(dimethylsiloxane) demonstrates that covalent bond scission contributes significantly to irreversible ...stress‐softening upon the initial extension, known as the Mullins effect. The cross‐linkers contain dioxetanes that emit light upon force‐induced bond scission. The filled elastomer emits light in cyclic uniaxial tension, but only on exceeding the previous maximum strain. The amount of light increases with hysteresis energy in a power law of exponent 2.0, demonstrating that covalent bond scission becomes increasingly important in the strain regime studied. Below 100%–120% strain, corresponding to energy absorption of (0.082 ± 0.012) J cm−3, mechanoluminescence is not detectable. Calibration of the light intensity indicates that by 190% strain, less than 0.1% of the dioxetane moieties break. Small but significant amounts of light are emitted upon unloading, suggesting a complex stress transfer to the dioxetanes mediated by the fillers. Pre‐strained material emits light on straining perpendicularly, but not parallel to the original tensile direction, demonstrating that covalent bond scission is highly anisotropic. These findings show that the scission of even a small number of covalent bonds plays a discernible role in the Mullins effect in filled silicone elastomers. Such mechanisms may be active in other types of filled elastomers.
Applying cycles of tensile strain to silica‐filled poly(dimethylsiloxane) functionalized with 1,2‐dioxetanes leads to the emission of mechanically induced chemiluminescence as covalent bonds break in the material. Monitoring in real time, light emission is observed predominantly on the first cycle to a strain. Covalent bond scission is shown conclusively to contribute to Mullins stress‐softening and to exhibit strong anisotropy.
There are differences in Sensory Processing Sensitivity (SPS) within many species. In humans high SPS refers to greater responsivity to stimuli, slower, deeper processing, aesthetic sensitivity, and ...low threshold for sensory discomfort. This study tested whether SPS is associated with the accurate recognition of degraded auditory stimuli and susceptibility to auditory pareidolia (hearing illusory words when presented with ambiguous, degraded words). Fifty participants (mean age = 33.02; females n = 32, males n = 18) responded to degraded words presented in Deutsch's phantom word illusion task. They then completed the Highly Sensitive Person Scale, which assesses SPS, and the Survey of Anomalous Experiences. SPS was significantly associated with the recognition of degraded stimuli, but not with pareidolia. Number of anomalous experiences reported by participants was significantly associated with SPS and pareidolia. This study shows objective validation of the Highly Sensitive Person Scale regarding detection of subtle external stimuli.
•There are differences in Sensory Processing Sensitivity (SPS) within many species.•High SPS refers to greater responsivity to stimuli, and slower, deeper processing.•High SPS is associated with accurate detection of degraded auditory stimuli.•High SPS is not associated with hearing illusory words in degraded auditory stimuli.•High SPS and pareidolia are associated with anomalous and paranormal experiences.
A chemiluminescent mechanophore, bis(adamantyl-1,2-dioxetane), is used to investigate the covalent bond scission resulting from the sorption of chloroform by glassy poly(methyl methacrylate) (PMMA) ...networks. Bis(adamantyl)-1,2-dioxetane units incorporated as cross-linkers underwent mechanoluminescent scission, demonstrating that solvent ingress caused covalent bond scission. At higher cross-linking densities, the light emission took the form of hundreds of discrete bursts, widely varying in intensity, with each burst composed of 107–109 photons. Camera imaging indicated a relatively slow propagation of bursts through the material and permitted analysis of the spatial correlation between the discrete bond-breaking events. The implications of these observations for the mechanism of sorption and fracture are discussed.
Previous research finds that marriage is associated with better health and lower mortality, and one of the mechanisms underlying this association is health-related selection out of marriage. Using ...longitudinal survey data from 2,348 couples from the Fragile Families and Child Wellbeing Study, we examine whether certain health behaviors-smoking and binge drinking-are associated with risk of union dissolution among couples with young children. We use discrete time hazard models to test whether associations between health behaviors and union dissolution differ between married and cohabiting parents. We find no statistically significant association between binge drinking and union dissolution for either cohabiting or married couples. Parental smoking, however, is associated with union dissolution. On average, married and cohabiting couples in which both parents smoke have a higher risk of union dissolution than couples in which neither parent smokes. Additionally, father's smoking (in couples in which the mother does not smoke) is associated with union dissolution, but only for married couples. These findings illustrate the importance of considering the health behaviors of both partners and provide further evidence of differences in union dissolution dynamics between married and cohabiting couples.
Poor health may destabilize romantic unions by impeding fulfillment of family responsibilities, increasing stress, and causing financial strain. We hypothesized that the associations of health ...characteristics with union stability for parenting couples vary by the gender of the partner in poor health and the couple’s marital status because of gender and marital status differences in family responsibilities and health-related coping behaviors. Using longitudinal data from the Fragile Families and Child Wellbeing Study (n = 2,997), we examined how three health measures predicted union dissolution for urban married and cohabiting couples with young children. Fathers’ depression at baseline predicted dissolution for all parenting couples, as did either partner developing depression between baseline and the following interview. For married parents, fathers’ health-related work limitations and mothers’ poor self-rated health also predicted dissolution. Associations between health conditions and dissolution differ by gender and marital status, possibly reflecting varying social norms about family responsibilities.
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