Packing microstructures and thermal properties of compressed emulsions: Effect of droplet size

Abstract

In preparing thermodynamically metastable emulsions, the droplets tend to coalesce. Consequently, it is difficult to investigate the properties of a monodisperse compressed emulsion experimentally or by simulations. At a specified volume fraction, the properties of emulsions vary with the droplet size but the relevant studies are very limited. The dissipative particle dynamics simulations are adopted to explore the highly concentrated emulsion of monodisperse droplets. Prior knowledge of the microstructure and inter-droplet interaction is not required. The critical packing associated with the onset of the jammed structure can be identified from the growth of the projected area and perimeter of droplets with the volume fraction (ϕ), ϕc ≈ 0.65. The mean coordination number (Z) from the radial distribution function rises with increasing the volume fraction, and can be described by the scaling relation (Z-Zc) ∼ (ϕ-ϕc)0.82 with Zc ≈ 6.3. The effects of the volume fraction, droplet diameter (D), and interfacial tension (σ) on the internal energy (U) and heat capacity (Cv) are studied systematically. Both U and Cv are found to grow as ϕ and σ are increased but D is decreased. According to dimensional analysis, all the data points can be well represented by the scaling relations (Cv − Cv,c) ∼ ϕ(ϕ − ϕc)1/3(σ/D) and (U − Uc) ∼ ϕ(ϕ − ϕc)1/3(σ/D).