Solute and particle self-assembly in sessile droplet on patterned substrate

• Main Author: Teo, Alistair Guo Hao
• Other Authors: Fei Duan
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/159130
• Institution: Nanyang Technological University

Bi-dispersed colloidal self-assembly on a patterned substrate may offer a new perception of how particles self-assemble and provide a future reference to improve industrial applications which include ink-jet printing, surface coating, and biosensors. Here, the investigation covers the droplet evaporation evolution, final patterning, particle-particle and particle-substrate interaction under the effect of bi-dispersed particles (3µm and 10µm) at different mixture percentages and concentrations levels. The PMMA patterned substrate first offers a hydrophobic surface property as contact angles higher than 100° are observed across all suspended droplets. The substrate also offers an initial octagonal wetting regime under the effect of square-based pyramid cavity patterning. The droplet evaporation stages can be sub-divided into CCR and stick-slip mode. Except for all the 0.1% concentration mixtures, the dominant mode of evaporation is CCR. All solutions of 0.1% concentration evaporate with CCR and transit into stick-slip mode at the last quarter of evaporating process. The depinning that took place in the last quarter of the evaporation process, suggests that minimum deposition of particles near the CL region is required for preventing CL withdrawal. The spread of the wetting regime is higher along the LS 45° than along the LS 0° as the array of pattern structures constructed is less resistive along LS 45°. This suggests that geometrical variables of the patterning can be further explored to create different sizes of final deposition patterns. At 20%(3µm)-80%(10µm) suspended solution, a “dome” structure with conical even distribution of central deposition ring at a peak height of 47.8µm is recorded at 2.6% concentration. The octagonal patterning is not prominent in this mixture as the outward capillary flow does not affect the agglomerated particles. In the mixture of 50%(3µm)-50%(10µm), the peak value decreases to 45.9µm but the particles are distributed across the octagonal wetting regime rather than centrally deposited. At 75%(3µm)-25%(10µm) mixture percentage, the “dome” structure did not manifest, but CRE is increasing at increasing concentration levels. At 2.6% concentration level, the particles are evenly spread and regularly distributed with a 14.2µm peak value recorded near the CL region rather than at the central region. Feasibly, future work on incorporating 3 or more different sizes of particles with different geometrical patterning substrates may offer new self-assembly behaviour to create new deposition patterning or structure due to the different agglomeration effects.