Systemic experiments have been conducted to investigate the effect of drop sizes on the rheology of water-in-oil (W/O) emulsions. Three sets of emulsions with different average drop sizes were first prepared and then the corresponding rheologies were determined using a concentric viscometer. Results indicated that the flow behavior of concentrated emulsions changes qualitatively from Newtonian flow to non-Newtonian flow with shear rates. In Newtonian flow regime, a smaller drop size leads to a higher viscosity, and the increments are more pronounced at high dispersed phase volume fractions. Two local remarkable increases of the emulsion viscosity with dispersed phase volume fractions correspond to the percolation and glass-transition, respectively. In non-Newtonian flow regime, emulsions show shear-thinning behavior and can be fitted well by the power law model. For emulsions with volume fractions between 0.132 and 0.325, the flow index and consistency constant show power law relationship with the water content. Furthermore, the shear-thinning effect becomes stronger in the emulsions with smaller drop sizes. A correlation has been successfully developed for determining the clusters’ sizes in W/O emulsions and shows excellent agreement with the experimental data. As a consequence, a microscopic understanding (cluster level) was presented for the shear-thinning behavior of the emulsions in this study. GRAPHICAL ABSTRACT

The effects of a typical anti-agglomerant, sorbitan monooleate (Span80), on the interactions between cyclopentane (CyC5) hydrate particles and water droplets were investigated using a micromechanical force (MMF) apparatus. The concentration of Span80 in CyC5 was ranged from 0.01 wt% to 1 wt%, and the experimental temperature was set at 1.5°C and 7°C, respectively. The results indicate that the absorption of Span80 on the droplet surface can render the interfaces more stable, preventing hydrate agglomeration. When the preload/contact force exceeds the strength of the interface (< ∼ 10 µN), the droplet ruptures, and the subcooling influences the interaction behavior significantly. At the lower temperature (1.5°C), the water droplet can spontaneously spread over the whole hydrate particle due to the significant reduction in water–CyC5 interfacial tension, and the water converts into hydrate rapidly. In this case, Span80 actually accelerates the agglomeration process and grants much shorter time to allow the external force to separate the water droplet and hydrate particle. At the higher temperature (7°C), the capillary bridge dominates the interaction behavior. The addition of Span80 reduced the capillary force through reducing the water–CyC5 interfacial tension. The measurements and observations in the present work can provide new insights into the mechanism of Span80 on inhibiting hydrate agglomeration. GRAPHICAL ABSTRACT