Observation of asphalt binder microstructure with ESEM

The observation of asphalt binder with the environmental scanning electron microscope (ESEM) has shown the potential to observe asphalt binder microstructure and its evolution with binder aging. A procedure for the induction and identification of the microstructure in asphalt binder was established in this study and included sample preparation and observation parameters. A suitable heat‐sampling asphalt binder sample preparation method was determined for the test and several stainless steel and Teflon sample moulds developed, finding that stainless steel was the preferable material. The magnification and ESEM settings conducive to observing the 3D microstructure were determined through a number of observations to be 1000×, although other magnifications could be considered. Both straight run binder (PG 58‐28) and an air blown oxidised binder were analysed; their structures being compared for their relative size, abundance and other characteristics, showing a clear evolution in the fibril microstructure. The microstructure took longer to appear for the oxidised binder. It was confirmed that the fibril microstructure corresponded to actual characteristics in the asphalt binder. Additionally, a ‘bee’ micelle structure was found as a transitional structure in ESEM observation. The test methods in this study will be used for more comprehensive analysis of asphalt binder microstructure.     

Effect of treatment temperature on the microstructure of asphalt binders: insights on the development of dispersed domains

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.     

Evolution of the microstructure of unmodified and polymer modified asphalt binders with aging in an accelerated weathering tester

This paper presents findings on the evolution of the surface microstructure of two asphalt binders, one unmodified and one polymer modified, directly exposed to aging agents with increasing durations. The aging is performed using an accelerated weathering tester, where ultraviolet radiation, oxygen and an increased temperature are applied to the asphalt binder surface. Ultraviolet and dark cycles, which simulated the succession of day and night, alternated during the aging process, and also the temperature varied, which corresponded to typical summer day and night temperatures registered in the state of Qatar. Direct aging of an exposed binder surface is more effective in showing microstructural modifications than previously applied protocols, which involved the heat treatment of binders previously aged with standardized methods. With the new protocol, any molecular rearrangements in the binder surface after aging induced by the heat treatment is prevented. Optical photos show the rippling and degradation of the binder surface due to aging. Microstructure images obtained by means of atomic force microscopy show gradual alteration of the surface due to aging. The original relatively flat microstructure was substituted with a profoundly different microstructure, which significantly protrudes from the surface, and is characterized by various shapes, such as rods, round structures and finally ‘flower’ or ‘leaf’ structures.     

Optical characterization of temperature‐ and composition‐dependent microstructure in asphalt binders

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 . 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 reveal hysteresis that closely resembles that observed by optical scatter, suggesting that thermally driven changes in microstructure volume fraction cause corresponding changes in .     

New direct observations of asphalts and asphalt binders by scanning electron microscopy and atomic force microscopy

Observations made using AFM and SEM have been combined in order to study the structure of asphalts. Fluorescence microscopy was used to aid in understanding the structural changes occurring when polymer is added to the asphalts.   With the atomic force microscope we are able to study the structure of the asphalts without any pre-preparation. Despite very low resolution, our study reveal ed a network of asphaltene molecules with regard to asphalt gel. The same result is obtained by SEM observation but with a much better resolution. SEM observation, however, needs an adequate preparation method.   In the presence of polymer we observed a rearrangement of the initial asphaltene association which leads to the assumption that polymer can aggregate the asphaltene phase.     

A comparative study on the self‐assembly of an amyloid‐like peptide at water–solid interfaces and in bulk solutions

In the past years the self‐assembly of amyloid‐like peptides has attracted increasing attentions, because it is highly related to neurodegenerative diseases and has a potential for serving as nanomaterial to fabricate novel and useful nanostructures. In this paper, we focused on the role of interfacial conditions in the self‐assembly of an amyloid‐like peptide, termed Pep11. It was found that, when dissolved in bulk solutions, Pep11 formed into β‐sheet structures and assembled into long filaments in several hours, as revealed by Thioflavin T fluorescence and transmission electron microscopy (TEM) morphology characterization, respectively. When the peptide solution was added onto a mica/HOPG substrate, peptide filaments with three preferred orientations with an angle of 60° to each other were formed immediately, as imaged in situ by atomic force microscopy (AFM). However, the kinetics in filament formation and the morphologies of the formed beta sheet either on HOPG and mica or in bulk solutions were quite different. These results indicate that the interfacial properties dramatically affect the peptide self‐assembly process. Microsc. Res. Tech. 78:375–381, 2015. © 2015 Wiley Periodicals, Inc.     

Influence of Ca content and oxygen partial pressure on microstructural evolution of (Co,Ca)O at elevated temperatures

Ca‐doped (1, 1.7, 5 and 10 mol% CaO) cobalt oxide single‐crystal samples, with an [001] orientation, were annealed at elevated temperatures of 1000–1200 °C for different times and at different oxygen partial pressures. The microstructure was examined by means of transmission light and electron microscopy. High‐temperature X‐ray diffractometry was used, with the aim of determining the temperature of the CoO ? Co₃O₄ transition in these materials. Extensive precipitation of Ca‐free Co₃O₄ spinel crystals was observed with increasing Ca content and oxygen activity. It is suggested that the electrical conductivity changes in this material may be related to this precipitation, because it changes the electronic state of cobalt cations.