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.

中文翻译：

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气、液、固界面沥青结合料微观结构的形态和动力学

我们结合光学和原子力显微镜观察微观结构（通常称为蜜蜂）的形态和动力学，这些微观结构在未改性的 Performance Graded (PG) 64-22 沥青结合料从 150°C 冷却至室温 (RT) 的自由表面形成在 5°C min-1 下，当表面以透明固体（玻璃）或液体（甘油）覆盖层终止时，这些微观结构会发生变化。主要发现是：（1）在游离粘合剂表面，在接近饱和物（如通过差示扫描量热法观察到的蜡）的结晶温度（~45°C）附近开始形成起皱的微观结构，然后增长到~5 µm 直径，~25 nm冷却至室温后，皱纹幅度和 10-30% 的表面积覆盖率，它们无限期地持续存在，形状或密度没有可观察到的变化。(2) 与初始冷却至室温后的游离粘合剂表面相比，冷却过程中粘合剂表面的甘油覆盖减少了起皱面积和起皱幅度；在室温下持续甘油覆盖在约 4 小时内消除了大多数表面微结构。(3) 没有观察到在覆盖有玻璃的粘合剂表面形成表面微结构。(4) 通过近红外显微镜观察所有粘合剂样品表面下方的亚微米块状微观结构，其尺寸、形状和密度与表面覆盖率无关。没有观察到这种结构有漂浮到毫米厚样品顶部或下沉到底部的趋势。(5) 基于薄膜连续介质力学模型，我们将表面起皱对表面覆盖率的依赖性归因于界面张力的变化。