Hydrophilic chips are preferred for making oil-in-water (O/W) emulsions, while water-in-oil (W/O) emulsions are best prepared in a hydrophobic chip.
So depending on the chip material, a hydrophobic or hydrophilic nanocoating may be required to obtain the desired surface wettability. Beside ‘simple’ O/W or W/O emulsions, more complex combinations are also possible, e.g. double emulsions consisting of three alternating oil and water layers (i.e. O/W/O or W/O/W). For some applications, double emulsions have considerable benefits. For example, it has been shown that water-soluble drugs are released at a controlled rate from double emulsions over a longer period of time compared to single emulsions.