Degree

Doctor of Philosophy (PhD)

Department

Department of Mechanical Engineering

Document Type

Dissertation

Abstract

Lab-on-a-chip technologies are widely applied in the field of life sciences and potentially in clinical diagnostics. There is a high demand for standardized, efficient interconnects between components in modular microfluidic systems. Chip-to-chip contactless, microfluidic interconnects, that allow fluid flow between chips, were designed and evaluated. The interconnects are 'gasketless' without the need for O-ring’s or fillers. Specifically, two microfluidic chips are assembled face-to-face and the fluidic ports on each chip were accurately aligned to allow the passage of fluids, through liquid bridges spanning the gap. Formation of the liquid bridges was governed by superhydrophobic films coating the surface around the fluidic ports to prevent leakage by the action of capillary forces modeled by the Laplace equation.

Three types of superhydrophobic coating films were fabricated: 1) spin coating of silica particles and epoxy resin, 2) spin coating of silica particles followed by NIL (Nano-imprint Lithography), and 3) spin coating of silica particles and silica oligomers. All those three types of films were evaluated in terms of their superhydrophobicity, transparency, and robustness. The resulting surface films had water contact angles of 162° ± 3° and a sliding angle of 3° ± 2°. The coatings remained superhydrophobic after 30 min of droplet impacts or 3 cycles of tape peeling. The spin coated superhydrophobic films were also highly transparent with transmittance of 82.5% ± 16% in the visible region.

A set of reconfigurable, multi-port chips with up to ten fluid interconnects in series was used to characterize the performance of the seals and assembled using magnetic discs to and pin-in-v-groove structures to align them. The multi-port chips allowed DI water, an ethanol/water mixture with surface tensions ranging from 38.56 to 72.75 mN/m, and plasma, to successfully pass through all ten fluid interconnects and the intervening microchannels without leakage at maximum flow rate at 100 μl/min.

The high-density, rapidly assembled, gasketless seal technology is applicable for chip-to-chip interconnections in complex microfluidic assemblies. To demonstrate the potential application of superhydrophobic surface in modular microfluidic systems, a mini-uMPS device was fabricated and tested. The superhydrophobic, gasketless interconnects did not leak for fluid flow between the motherboard and two modules of the mini-uMPS device at flow rate of 20 μl/min and pressure drop of 3.71 psi.

Date

7-9-2019

Committee Chair

Murphy, Michael C.

Available for download on Monday, July 06, 2026

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