Summary
We combined optical and atomic force microscopy to observe morphology and kinetics of microstructures (typically referred to as bees) that formed at free surfaces of unmodified Performance ...Graded (PG) 64‐22 asphalt binders upon cooling from 150°C to room temperature (RT) at 5°C min–1, and changes in these microstructures when the surface was terminated with a transparent solid (glass) or liquid (glycerol) overlayer. The main findings are: (1) at free binder surfaces, wrinkled microstructures started to form near the crystallization temperature (∼45°C) of saturates such as wax observed by differential scanning calorimetry, then grew to ∼5 µm diameter, ∼25 nm wrinkle amplitude and 10–30% surface area coverage upon cooling to RT, where they persisted indefinitely without observable change in shape or density. (2) Glycerol coverage of the binder surface during cooling reduced wrinkled area and wrinkle amplitude three‐fold compared to free binder surfaces upon initial cooling to RT; continued glycerol coverage at RT eliminated most surface microstructures within ∼4 h. (3) No surface microstructures were observed to form at binder surfaces covered with glass. (4) Submicron bulk microstructures were observed by near‐infrared microscopy beneath the surfaces of all binder samples, with size, shape and density independent of surface coverage. No tendency of such structures to float to the top or sink to the bottom of mm‐thick samples was observed. (5) We attribute the dependence of surface wrinkling on surface coverage to variation in interface tension, based on a thin‐film continuum mechanics model.
Lay Description
Asphalt binder, or bitumen, is the glue that holds aggregate particles together to form a road surface. It is derived from the heavy residue that remains after distilling gasoline, diesel and other lighter products out of crude oil. Nevertheless, bitumen varies widely in composition and mechanical properties. To avoid expensive road failures, bitumen must be processed after distillation so that its mechanical properties satisfy diverse climate and load requirements. International standards now guide these mechanical properties, but yield varying long‐term performance as local source composition and preparation methods vary. In situ diagnostic methods that can predict bitumen performance independently of processing history are therefore needed. The present work focuses on one promising diagnostic candidate: microscopic observation of internal bitumen structure. Past bitumen microscopy has revealed microstructures of widely varying composition, size, shape and density. A challenge is distinguishing bulk microstructures, which directly influence a binder's mechanical properties, from surface microstructures, which often dominate optical microscopy because of bitumen's opacity and scanning‐probe microscopy because of its inherent surface specificity. In previously published work, we used infrared microscopy to enhance visibility of bulk microstructure. Here, as a foil to this work, we use visible‐wavelength microscopy together with atomic‐force microscopy (AFM) specifically to isolate surface microstructure, to understand its distinct origin and morphology, and to demonstrate its unique sensitivity to surface alterations. To this end, optical microscopy complements AFM by enabling us to observe surface microstructures form at temperatures (50°C–70°C) at which bitumen's fluidity prevents AFM, and to observe surface microstructure beneath transparent, but chemically inert, liquid (glycerol) and solid (glass) overlayers, which alter surface tension compared to free surfaces. From this study, we learned, first, that, as bitumen cools, distinctly wrinkled surface microstructures form at the same temperature at which independent calorimetric studies showed crystallization in bitumen, causing it to release latent heat of crystallization. This shows that surface microstructures are likely precipitates of the crystallizable component(s). Second, a glycerol overlayer on the cooling bitumen results in smaller, less wrinkled, sparser microstructures, whereas a glass overlayer suppresses them altogether. In contrast, underlying smaller bulk microstructures are unaffected. This shows that surface tension is the driving force behind formation and wrinkling of surface precipitates. Taken together, the work advances our ability to diagnose bitumen samples noninvasively by clearly distinguishing surface from bulk microstructure.
For clinical studies of sarcopenia and frailty, clinically meaningful outcome measures are needed to monitor disease progression, evaluate efficacy of interventions, and plan clinical trials. ...Physical performance measures including measures of gait speed and other aspects of mobility and strength have been used in many studies, although a definition of clinically meaningful change in performance has remained unclear. The International Conference on Frailty and Sarcopenia Research Task Force (ICFSR-TF), a group of academic and industry scientists investigating frailty and sarcopenia, met in Miami Beach, Florida, USA in February 2019 to explore approaches for establishing clinical meaningfulness in a manner aligned with regulatory authorities. They concluded that clinical meaningful change is contextually dependent, and that both anchor- based and distribution-based methods of quantifying physical function are informative and should be evaluated relative to patient-reported outcomes. In addition, they identified additional research needed to enable setting criteria for clinical meaningful change in trials.
Two new doubly interpenetrated metal-organic frameworks (MOFs) with formulas {Zn(L1)(5-nipa)}·DMAα (1a) and {Cd(L2)(5-nipa)(H2O)}α (1b) have been discussed herein, where ...L1 = N,N'-(oxybis(4,1-phenylene))diisonicotinamide; L2 = N,N'-(methylenebis(4,1-phenylene)) diisonicotinamide; 5-H2nipa = 5-nitroisophthalic acid; DMA = dimethylacetamide. A single crystal X-ray analysis reveals that 1a exhibits a 2D-interpenetrated interwoven sheet and finally adapts a 3D framework structure with the help of π···π stacking interactions. Similarly, 1b displays a two-fold interpenetrated 2D sheet-like architecture and is finally adjusted to a 3D structure. Both 1a and 1b feature channels with a cross-section of 25.06 × 25.06 Å2 and 24.01 × 24.01 Å2, respectively, running along the b-axis. Topological analysis of 1a and 1b by ToposPro suggests a (4)-connected uninodal sql topology with point symbol {44.62}. Further, 1a and 1b were exploited as molecular sensors for several amino acids exposing different shapes and sizes and exhibiting selective turn-on fluorescence sensing towards biologically important D/L-tryptophan with the notable limit of detection values of 0.084/0.110 μM and 0.143/0.141 μM, respectively, in aqueous medium. In addition, 1a and 1b were also exploited as heterogeneous catalysts towards several assorted aldehydes having different electronic environments, including sterically demanding aldehydes, under mild reaction conditions and obtained up to 97% of the respective Knoevenagel condensation product. Importantly, sterically hindered aldehydes also worked well with the MOF catalysts 1a and 1b, but showed comparatively low conversion. It is important to mention that in both cases, these MOF materials are recyclable for up to five consecutive runs without displaying any substantial loss in their sensing or catalytic activities. Moreover, the present investigation cultivates a new vision to design novel luminescent MOFs that can be used as multifunctional materials for the turn-on sensing of small organic molecules as well as instigated as heterogeneous catalysts in diverse organic transformation reactions.
Two new MOFs have been prepared and exploited as a bifunctional material for the selective recognition of amino acids and substrate selective Knoevenagel condensation reactions having the industrial importance. Display omitted
•Two new MOFs with formulas {Zn(L1)(5-nipa)}·DMAα (1a) and {Cd(L2)(5-nipa)(H2O)}α (1b) have been synthesized.•Both MOFs were exploited as luminescent probes for the sensing of amino acids.•Both MOFs displayed selective and sensitive detection of D/L-tryptophan as turn-on sensors.•Both MOFs behaved as efficient heterogeneous catalysts for the Knoevenagel condensation reaction.
Summary
We introduce noncontact optical microscopy and optical scattering to characterize asphalt binder microstructure at temperatures ranging from 15°C to 85°C for two compositionally different ...asphalt binders. We benchmark optical measurements against rheometric measurements of the magnitude of the temperature‐dependent bulk complex shear modulus |G*(T)|. The main findings are: (1) Elongated (∼5 × 1 μm), striped microstructures (known from AFM studies as ‘bees’ because they resemble bumble‐bees) are resolved optically, found to reside primarily at the surface and do not reappear immediately after a single heating–cooling cycle. (2) Smaller (∼1 μm2) microstructures with no observable internal structure (hereafter dubbed ‘ants’), are found to reside primarily in the bulk, to persist after multiple thermal cycles and to scatter light strongly. Optical scattering from ‘ants’ decreases to zero with heating from 15°C to 65°C, but recovers completely upon cooling back to 15°C, albeit with distinct hysteresis. (3) Rheometric measurements of |G*(T)| reveal hysteresis that closely resembles that observed by optical scatter, suggesting that thermally driven changes in microstructure volume fraction cause corresponding changes in |G*(T)|.
Lay description
Most paved roads are built using asphalt mixtures that consist of mineral aggregates held together by a binder, or ‘glue’, that governs a road's mechanical properties. This ‘glue’, called bitumen or asphalt binder, is a viscous hydrocarbon emulsion distilled from petroleum. Pavement grade bitumen must be fluid enough to be pumped, worked and mixed during paving, yet stiff enough after paving to resist rutting in hot weather, and soft enough to resist cracking in cold weather. These demanding, and partly conflicting, requirements have engendered extensive research to understand and optimize the chemical makeup and microscopic characteristics of bitumen that control its macroscopic mechanical properties.
Under an optical microscope, bitumen that appears uniform in texture to the unaided eye exhibits a rich array of bacteria‐size inclusions. Here, we find that some of these inclusions reside on the surface, are best observed with green light, and can be prevented from forming by preparing samples under a cover slip. Other smaller inclusions pervade the bulk, are best observed with near infrared light, and survive indefinite thermal cycling. We employ near infrared optical microscopy to measure the volume fraction of two chemically distinct pavement‐grade bitumen varieties that these bulk inclusions occupy as we vary sample temperature between 15°C and 65°C. Upon slow heating, this volume fraction at first grows, then shrinks to zero. Upon slow cooling, the volume fraction is as much as 78–92% smaller (depending on the bitumen variety) at a given temperature than during heating, although it returns to its original value after cooling back to 15°C. In parallel with these microscopic measurements, we employ a rheometer to measure variations in stiffness of these two bitumen varieties as we vary their temperature over the same range. We observe that the stiffness of both varieties reduces upon heating, and recovers upon cooling. But most significantly, we observe a 15–23% discrepancy in stiffness at any given temperature between the heating and cooling cycles that mirrors the behavior of the microscopic inclusions. This behavior reproduces during subsequent thermal cycles. The significance of these results is that they establish a direct, quantitative correlation, and suggest a causal connection, between the volume fraction occupied by the inclusions and the stiffness of bitumen. They also demonstrate that optical microscopy can play a key role in fast, noncontact screening and testing of asphalt binders.
The detrimental effects of water in asphalt mixtures and its manifestation as distresses in asphalt pavements were first recognised in the 1930s and have been studied extensively during the last 35 ...years. This deterioration process, referred to as moisture damage, is generally defined as the degradation of the mechanical properties of the material due to the presence of moisture in its microstructure. Moisture damage is a complex phenomenon that involves thermodynamic, chemical, physical and mechanical processes. This paper describes the processes by which moisture damage affects asphalt mixtures. A critique of various moisture damage mechanisms is presented, followed by a review of recent work on modes of moisture transport (i.e. water permeability, capillary rise and vapour diffusion) and their relationship to moisture damage. Special attention is given to the characterisation of void structures of asphalt mixtures, which is an important factor that influences moisture transport. Finally, the paper presents a review of existing theories on the adhesive bond between aggregates and asphalt binders and the effect of the presence of moisture at the interface. The mechanisms described in the paper are complemented by a second paper that presents recent advances in moisture damage characterisation using experimental methods, analytical-based approaches (i.e. fracture mechanics, continuum mechanics, thermodynamics and micromechanics), and numerical modelling.
Summary
This paper offers important insights on the development of the microstructure in asphalt binders as a function of the treatment temperature. Different treatment temperatures are useful to ...understand how dispersed domains form when different driving energies for the mobility of molecular species are provided. Small and flat dispersed domains, with average diameter between 0.02 and 0.70 μm, were detected on the surface of two binders at room temperature, and these domains were observed to grow with an increase in treatment temperature (up to over 2 μm). Bee‐like structures started to appear after treatment at or above 100°C. Moreover, the effect of the binder thickness on its microstructure at room temperature and at higher treatment temperatures was investigated and is discussed in this paper. At room temperature, the average size of the dispersed domains increased as the binder thickness decreased. A hypothesis that conciliates current theories on the origin and development of dispersed domains is proposed. Small dispersed domains (average diameter around 0.02 μm) are present in the bulk of the binder, whereas larger domains and bee‐like structures develop on the surface, following heat treatment or mechanical disturbance that reduces the film thickness. Molecular mobility and association are the key factors in the development of binder microstructure.
Lay description
The present paper offers insights about the development of the superficial microstructure of asphalt binders. The microstructure of asphalt binder is composed of two main phases, the matrix and the dispersed phase. In this paper, it was observed that the treatment temperature influences the resulting microstructure: if the treatment temperature increases, the dispersed domains increase in size. It was also observed that if no heat treatment is performed, the dispersed domains are very small, and they increase in size with deceasing binder thickness. Molecular mobility was found to be the key factor in the development of the binder microstructure.
Summary
We use near‐infrared dark‐field optical microscopy to probe isothermal time variation of the volume fraction of naturally‐occurring, subsurface microstructures in PG 64‐22 asphalt binders at ...temperature T=30∘C, following a rapid heating (cooling) increment |ΔT|=20∘C from initial temperature T0=10∘C(50∘C). We compare these microstructure variations with isothermal time variations of the magnitude |G30∗(t)| of the bulk complex shear modulus measured for identical sample conditions with a Dynamic Shear Rheometer. The main findings are: (1) Microstructure volume fraction (inferred from intensity I(t) of near‐infrared optical scatter) and |G∗(t)| both continue to change appreciably long after measurable changes of binder temperature cease. Moreover, delayed time variations in I(t) and |G∗(t)| (2) correlate closely with each other; (3) evolve on three distinct time scales – several minutes, ∼1 h, >1 day; (4) depend on binder aging; (5) are more pronounced after a cooling step (ΔT=−20∘C) than after a heating step (ΔT=+20∘C); and (6) account for hysteresis in I(t) and |G∗(t)| curves observed during heating–cooling cycles.
Lay Description
Typical paved roads are designed by combining asphalt binder, also known as bitumen, with various aggregates like gravel, rocks and sand. The bitumen is the glue that holds the aggregates together and it is the primary factor that determines a road's mechanical properties. When crude oil is distilled, lighter products, such as gas and diesel, are removed, and the heaviest residue, bitumen, is what remains. After distillation, bitumen is processed in order to meet site‐specific temperature and loading requirements. These requirements are determined by the climate in which the pavement will be located and the loads it will sustain. Pavements must be stiff enough to resist rutting and deformation in warm weather, and soft enough to resist cracking in cold weather. Optimizing bitumen to meet these strict and sometimes contradicting requirements is the topic of a considerable amount of research.
Although bitumen looks smooth and homogenous to the naked eye, under magnification it exhibits an abundance of micro‐scale structure that is related in poorly understood ways to the binder's strength. Previous literature has shown that both surface and bulk microstructures exist, and vary in composition, size and density. Here, we use near infrared light to observe selectively the microstructures that reside in the bulk of the bitumen, since these are the most important in determining the binder's strength. After subjecting bitumen samples of various chemical compositions to a 20°C temperature change within half a minute – mimicking a rapid change in weather – and allowing them to stabilize at their new temperature within 2 min, we watch bulk microstructure evolve over the next several hours, while measuring the binder's stiffness with a mechanical rheometer every few minutes. We find that microstructure volume fraction and stiffness both continue to change in closely correlated ways long after each sample's temperature stabilizes. Specifically, microstructure and stiffness evolve on three time scales – less than 1 min, about an hour and more than a day – following a similar mathematical function, allowing us to construct an empirical model relating microstructure to stiffness. These quantitative results account for structural hysteresis of bitumen observed and reported previously.
The significance of the results is that they link the internal microstructure of bitumen quantitatively to its mechanical properties. More generally, they contribute to developing predictive micromechanical models and bench‐top microscopic diagnostic procedures that support engineering of composite materials with desirable properties.
A test and analysis method to determine both the damage and healing characteristics of an asphalt composite using the same test specimen is presented. The test involves applying multiple stretches of ...load cycles, each separated by a period of zero load introduced at different levels of stiffness reduction. The analytical procedure involves using the modified correspondence principles and viscoelastic continuum damage mechanics to model damage and healing properties of the composite. The results obtained using two different asphalt mortars confirmed the findings from previous researchers that the characteristic pseudo-stiffness versus damage relationship for each material was independent of testing conditions. More importantly, this study demonstrated that the aforementioned relationship was also independent of the rest periods introduced intermittently during the fatigue test. Results also show that healing defined in terms of the change in the state variable of damage was independent of the conditions used to induce fatigue damage.
An efficient synthetic protocol affording symmetrical 1,2-bis(pyridine-2/3/4-yl)methyldiselanes from pyridine-2/3/4-carbaldehyde in high yields at room temperature, without using highly toxic ...hydrogen selenide, has been developed. The synthesis involves the reductive selenation of pyridine-2/3/4-carbaldehyde with sodium hydrogen selenide, NaHSe in the presence of piperidine hydrochloride followed by NaBH4 reduction under mild conditions. Primary screening of the anti-proliferative activity of the newly synthesized compounds against several mammalian cell lines and pathogenic strains has been carried out. The crystal structure of 1,2-bis(pyridine-3-yl)methyldiselane has been established by X-ray diffraction analysis.
Crystal structure of 1,2-bis(pyridine-3-yl)methyldiselane. Display omitted
•Synthesis of 1,2-bis(pyridinyl)methyldiselanes by reductive selenation is reported.•Base-catalyzed reductive selenation was carried out using sodium hydrogen selenide.•Current protocol affords high yields under mild conditions, avoiding toxic H2Se.•Anti-proliferative activity of diselanes against cancer and pathogenic cells studied.•Structure elucidation of 1,2-bis(pyridine-3-yl)methyldiselane by X-ray crystallography.
Individuals receiving hemodialysis often experience concurrent symptoms during treatment and frequently report feeling unwell after dialysis. The degree to which intradialytic symptoms are related, ...and which specific symptoms may impair health-related quality of life (HRQoL) is uncertain.
To explore intradialytic symptoms clusters, and the relationship between intradialytic symptom clusters with dialysis treatment recovery time and HRQoL.
We conducted a post hoc analysis of a prospective cohort study of 118 prevalent patients receiving hemodialysis in two centers in Calgary, Alberta and Hamilton, Ontario, Canada.
Adults receiving hemodialysis treatment for at least 3 months, not scheduled for a modality change within 6 weeks of study commencement, who could provide informed consent and were able to complete English questionnaires independently or with assistance.
Participants self-reported the presence (1 =
to 5 =
) of 10 symptoms during each dialysis treatment, the time it took to recover from each treatment, and weekly Kidney Disease Quality of Life 36-Item-Short Form (KDQoL-36) assessments. Principal component analysis identified clusters of intradialytic symptoms. Mixed-effects, ordinal and linear regression examined the association between symptom clusters and recovery time (categorized as 0, >0 to 2, >2 to 6, or >6 hours), and the physical component and mental component scores (PCS and MCS) of the KDQoL-36.
One hundred sixteen participants completed 901 intradialytic symptom questionnaires. The most common symptom was lack of energy (56% of treatments). Two intradialytic symptom clusters explained 39% of the total variance of available symptom data. The first cluster included bone or joint pain, muscle cramps, muscle soreness, feeling nervous, and lack of energy. The second cluster included nausea/vomiting, diarrhea and chest pain, and headache. The first cluster (median score: -0.56, 25th to 75th percentile: -1.18 to 0.55) was independently associated with longer recovery time (odds ratio OR 1.62 per unit difference in score, 95% confidence interval CI: 1.23-2.12) and decreased PCS (-0.72 per unit difference in score, 95% CI: -1.29 to -0.15) and MCS scores (-0.82 per unit difference in score, 95% CI: -1.48 to -0.16), whereas the second cluster was not (OR 1.24, 95% CI: 0.97-1.58; PCS 0.19, 95% CI -0.46 to 0.83; MCS -0.72, 95% CI: -1.50 to 0.06).
This was an exploratory analysis of a small data set from 2 centers. Further work is needed to externally validate these findings to confirm intradialytic symptom clusters and the generalizability of our findings.
Intradialytic symptoms are correlated. The presence of select intradialytic symptoms may prolong the time it takes for a patient to recover from a dialysis treatment and impair HRQoL.
PDF
