Controlled Evaporative Self-Assembly - Pattern Deposition - of Polymeric Solutions inside a Micro-Chamber

Mohammad Abo Jabal, Chemical Engineering, Technion, Hifa, Israel
Ofer Manor, Chemical Engineering, Technion, Hifa, Israel

Controlled evaporative self-assembly of deposits – pattern deposition – from volatile solutions or suspensions, is a process that enables the organization of soft and hard materials of interest including polymers, nanoparticles, and biomaterials into complex structures of high regularity. Nowadays, pattern deposition is being used by many companies to avoid expensive fabrication procedures; the most common of which is photolithography. The most common experimental procedure employed is the placing of a sessile droplet of a volatile solution or suspension on a solid surface. Nevertheless, this technique has limited ability to yield a reproducible, regular, and well defined patterns required for a thorough investigation of the physical mechanisms occurring during the deposition process.

We employ a simple model system, allowing for a well-defined experimental procedure in terms of geometry and ambient conditions. Our experimental system comprising a rectangular microfluidics chamber in which we inject a polymeric solution (PMMA in Toluene). During evaporation, the Toluene solution de-wets the solid surface of the chamber. The three-phase contact line between the solid substrate of the cell and the solution moves in a "stick-slip" motion while being aligned as a straight line due to the geometry of the cell. The deposition occurs when the contact line sticks to the substrate, producing periodic strips with width, thickness, and periodicity down to 1 µm, 20 nm, and 2 µm, respectively. In this presentation, we use our model experimental system to show the relation between the morphology of the deposited patterns and parameters governing the experimental procedure such as the concentration of the solution, the molecular mass of the polymer, the ambient temperature, the dimensions of the microfluidic chamber, and the spatiotemporal position of the meniscus of the liquid in the chamber.