Depletion forces between particles immersed in nanofluids

•Nanofluids may contain soft, self-assembled nanostructures of different size, shape and surface chemistry.•Phase transitions in binary colloidal mixtures with large size and geometry asymmetry can offer relevant insights.•Direct measurement of depletion and structural forces in nanofluids is limited.•The role of proteo-nanofluids mediated depletion in cellular organisation and biological processes is under-appreciated.•Many theoretical and experimental challenges and opportunities remain.

Understanding depletion forces between colloidal particles mediated by nanofluids, i.e. liquids containing hard or soft nanostructures, is immensely important in a number of industrial processes. We anticipate added complexities due to enhanced and multifactorial inter-depletant interactions associated with their size, shape, surface chemistry, and concentration. Here we briefly review recent efforts in direct measurement of depletion forces mediated by nanofluids, as well as a number of related studies on the phase transition in binary colloid mixtures with large size and shape asymmetry, a process in which depletion forces play an important role. We will also discuss the often under-appreciated importance of depletion forces mediated by proteo-nanofluids (liquids containing proteins) in facilitating cellular organisation. Some challenges and outstanding questions will emerge from the above discussions, as briefly summarised.

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