Impact of varying preparation methods of colloidal suspensions on droplet desiccation patterns on hydrophobic and hydrophilic substrates

Abstract

The patterns left by desiccating droplets of colloidal solutions form an integral part of a gamut of applications in technology, medicine and fundamental science. While almost all attention is reserved for understanding flow dynamics of drying droplets and the resulting dried droplet pattern with respect to variation of a host of parameters, there is almost a total absence of any discussion on the importance of the ‘mixing methods’ of solute and solvent during solution preparation. We demonstrate in this work, that desiccation patterns of colloidal solutions show an amazing variation in details, depending on the manner of solution preparation. The variation is achieved by simple mechanical treatment, namely magnetic stirring and ultrasonication, and for different stirring times. The suitable explanation of the striking variation in the dried droplets on both hydrophilic and hydrophobic substrates lead us to propose that the stirring time corresponding to a particular method adopted for solution preparation, results in varying degrees of paring of aggregates. We establish that a homogeneous colloidal solution can only be achieved by mixing for a minimum time t std , that is a function of a particular mixing procedure and a given solute-solvent combination. The prepared solution may then be used in different applications to obtain faithful standard results.