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Study of the characteristics of polymer droplet deposition in fabricated rectangular microcavities

Micro-flow visualization and computational fluid dynamics have been complementarily performed for studying microcavity deposition phenomena. A piezoelectric inkjet printhead is used to eject the poly(ethylenedioxythiophene) droplets onto rectangular microcavities. By varying the droplet Weber number (We) (9.9–39.4), sidewall contact angle (θs) (22°–50°) and microcavity length-to-width ratio (L/W) (1.00–3.30), various deposition characteristics in microcavities are examined and the critical We (Wec) for filling microcavities with uniform ink films are identified. The physics embedded in the newly observed hole formation in the spreading liquid film is disclosed. The difference in equilibrium deposition film patterns between the rectangular and square microcavities is also addressed. A single correlation governing the functional dependences of Wec on the normalized θs and L/W is deduced for the first time. The unified correlation is believed to provide useful engineering references for operating inkjet printheads and fabricating uniform thin film coating on the bottom substrate of microcavities.