Physical properties of interfacial layers formed at the water-xylene interface by the adsorption of a polyaromatic organic compound, N-(1-hexylheptyl)-N'-(5-carbonylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (in brief C5Pe), were studied systematically. The deprotonation of the carboxylic group of C5Pe at alkaline pH made it highly interfacially active, significantly reducing the water-xylene interfacial tension. Thin liquid film experiments showed a continuous build-up of heterogeneous C5Pe interfacial layers at water-xylene interfaces, which contributed to the formation of stable W/O emulsions. Continual accumulation and rearrangement of C5Pe aggregates at the water-xylene interface to form a thick layer was confirmed by in-situ Brewster angle microscopy (BAM) and atomic force microscopy (AFM). The rheology measurement of the interfacial layer by double wall ring interfacial rheometry under oscillatory shear showed that the interfacial layers formed from high C5Pe concentrations were substantially elastic and rigid. The presence of elastically dominant interfacial layers of C5Pe led to the formation of stable water-inxylene emulsions.Keywords: polyaromatic surface active compound, water-in-oil emulsions; thin liquid films; insitu Brewster angle imaging; interfacial rheology

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