Surface Morphology and Chemical Mapping of UV-Aged Thin Films of Bitumen

Abstract

This study decouples effects of ultraviolet (UV) exposure on the surface and bulk properties of bituminous composites. UV exposure accelerates oxidative aging of bitumen, but its effects are concentrated mostly at the surface of the bitumen. Here, we examine morphology and chemical composition of the surfaces of non-aged thin films of bitumen and UV-aged thin films of bitumen using combined atomic force microscopy (AFM) and photothermal infrared (AFM−IR) spectroscopy; we further compare the findings with those of bulk properties measured by Fourier transform infrared spectroscopy. The study results showed that the surfaces of non-aged and 20 h UV-aged bitumen appeared depleted in phenyl and CH 3 groups compared to the bulk. This in turn indicates that the surfaces lacked asphaltenes and aromatics. It also shows that the saturated aliphatics found on the surface were almost all nonbranched linear chains. The ratio of CH 3 /CH 2 between the surface and bulk was completely reversed as the aging progressed; the non-aged and 20 h UV-aged films showed a lower CH 3 /CH 2 ratio at the surface relative to the bulk, but the 50 h UV-aged film showed a higher ratio. The latter observation was attributed to the chain scission and start of decomposition reactions breaking down the large compounds into smaller ones. In addition, sulfur hydroxyls present in the bulk were entirely absent from the surface. Furthermore, the chemical composition of the bee like structures on the bitumen surface could not be easily distinguished from the bulk composition by AFM−IR, but they appeared to be depleted in alkenes and hydroxyls compared to the areas around them. The study outcomes show variational effects of UV exposure on surface and bulk properties of bituminous composites. Such insights help formulators and manufacturers design functionally graded bitumen composites with enhanced resistance to UV aging at the surface.

High resolution nanoscale chemical analysis of bitumen surface microstructures

“…A complete characterization of surface phases is only possible with the combination of different techniques: (a) Fluorescence microscopy studies have shown fluorescent centres which were attributed to aromatics and resin fractions 34 . (b) AFM-IR observed the same centres and recorded sulfoxide stretching mode of organic sulfate esters at 1080 cm −1 and carbonyl stretching of ketones at 1700 cm −1 for the para-phase 38 . (c) ToF–SIMS measurements found chemical heterogeneities on the surface, however, the typical microstructural features occurring on bitumen surface, catana, peri and para phase, could not be resolved by means of the main molecular components aromatics, saturates, resins and asphaltenes 15 .…”

Preparation and properties of water-based acrylic emulsion-assisted flexible building tiles

“…The morphology of flexible building tiles was further investigated by SEM. 37 To prove the enhanced compatibility by adding the WPAs, commercial emulsions (Shanghai Bao Li Jia Chemical Co., Ltd) were used as the control group. As illustrated in Fig.…”

Effects of Elemental Sulfur on the Aging Trajectory and Adhesion Characteristics of Rubber-Modified Bitumen

“…Pure elemental sulfur is stable under UV irradiation, but it has been shown to be a weak photocatalyst, capable of splitting water into reactive radicals . Although the penetration depth of UV light into bitumen is shallow, the physical and chemical effects at the surface can be extreme. − Even without added sulfur, oxidized sulfate (SO 4 ) minerals are a large proportion of the nonvolatile residue left behind after UV degradation of bitumen thin films …”