Pattern Deposition of Colloidal Particles in a Microfluidic Chamber: Role of DLVO Forces

Ekhlas Homede, Chemical Engineering, Technion, Haifa, Israel
Ofer Manor, Chemical Engineering, Technion, Haifa, Israel

Colloids play a fundamental role in many technological and biological domains, such as water treatment, industry, printing, and drug delivery. Controlled deposition of colloidal particles -pattern deposition- is employed for both exploiting the collective properties of the particles and their integration into applicative devices. Recently, many companies have shown an increased interest in deposition patterns from an evaporating suspensions or solutions as an efficient way to avoid expensive fabrication procedures like photolithography. However, the shape of the deposit of colloidal particles, obtained following the evaporation of the suspension, is still a challenging problem. Various patterns such as ring-like structure, mountain structures, and uniform deposits can be generated during the evaporation of a sessile drop; the interplay between colloidal and Marangoni forces, transport phenomena, and evaporation dynamics govern the process of deposition.

In this work, we employ a simple physical model comprising two parallel plates with rectangular geometry. The system studied involves aqueous suspension of varied size latex particles, evaporating from a micrometric gap on a substrate of silicon oxide. During evaporation, the aligned contact line moves in a “stick-slip” motion, where the deposition occurs in the stick mode producing periodic parallel stripes. Tuning different factors such as the particles size, concentration, presence of electrolytes, the rate of evaporation, and the presence of surfactants is shown to influence the obtained pattern of the deposited particles inside the chamber. The results of the experiment enable us to identify and quantify the influence of the different physical mechanisms taking place during the experimental procedure. In particular, we examine the influence of colloidal forces on the geometrical properties of the deposited patterns.