Particle and Substrate Charge Effects on Colloidal Self-Assembly in a Sessile Drop

Abstract

By direct video monitoring of dynamic colloidal self-assembly during solvent evaporation in a sessile drop, we investigated the effect of surface charge on the ordering of colloidal spheres. The in situ observations revealed that the interaction between charged colloidal spheres and substrates affects the mobility of colloidal spheres during convective self-assembly, playing an important role in the colloidal crystal growth process. Both ordered and disordered growth was observed depending on different chemical conditions mediated by surface charge and surfactant additions to the sessile drop system. These different self-assembly behaviors were explained by the Coulombic and hydrophobic interactions between surface-charged colloidal spheres and substrates.

Controlled and rapid ordering of oppositely charged colloidal particles

“…1a and 1b can be attributed to the strong electrostatic attraction between oppositely charged PS particles. As shown in a recent study [37], the attractive hydrophobic interaction can limit the mobilities of hydrophobic PS spheres. This is driven by the reduction in surface energy on coagulation of hydrophobic spheres and is consistent with our observations.…”

Transport and deposition patterns in drying sessile droplets

“…The velocity of arrival below which the ordered phase formed is apparently set by the ratio of the time between successful arrivals of new particles to a position along the contact line to the time required for particles to rearrange by diffusion near the contact line . Consistent with this, Yan et al showed that by changing the charge of the particles relative to that of the substrate, or by addition of surfactant, the mobility of the particles at the contact line could be increased or decreased, thereby controlling whether ordered or disordered particle assemblies formed. For example, particles of charge opposite that of the surface were relatively immobile and formed a disordered deposit, while the opposite occurred for particles of the same charge as the substrate.…”

In-situ microscope observation of the growth of 2D colloidal crystals in a sessile drop

“…In our previous work, we have studied the influence of charge, including sphere's surface charge, substrate's surface charge, and surfactant's charge, on the ordering of self-assembly process [20]. It was found that significantly ordered self-assembly is only achieved when the colloidal spheres and the substrate possess the same sign of surface charge.…”