Importance of thermal gradient in the bitumen bees genesis
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Bitumen can be regarded as a complex colloidal suspension. Indeed, the heaviest molecules in bitumen, the asphaltenes, are known to self-associate to form solid particles suspended in a fluid called maltenes. Bitumen is also composed of a crystallizable fraction that partitions between asphaltenes and maltenes. This complex colloidal system exhibits peculiar patterns at their surface called “bees.” By varying the bitumen formulation and also tuning process parameters such as the temperature cooling rate, we demonstrate the role of the various components: asphaltenes, maltenes, and the crystallizable fraction on the bee existence and we evidence that the bee formation results from a complex coupling between different physico-chemical phenomena such as phase separation, crystallization, and buckling. We then propose a mechanism of bee genesis based on the thermal properties of the various fractions and especially on the heat capacity of both asphaltenes and maltenes. We demonstrate that a thermal gradient in the sample is required for the formation of bees and put into evidence the importance of kinetic aspects. We also discuss the bitumen general bulk properties.
KeywordsAtomic Force Microscopy Cool Rate Bitumen Cold Spot Differential Scanning Calorimetry Experiment
We would like to thank the Association Nationale Recherche Technologie (ANRT) for the financial support of this study through the CIFRE contract number 2012/1210.
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