Identifier

etd-03312014-105753

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

The gasketless microfluidic interconnect has the potential to offer a standardized approach to interconnects between modular microfluidic components. This strategy uses parallel superhydrophobic surfaces (contact angle ≥ 150ᴼ) to passively seal adjacent, concentric, microfluidic ports separated by an air gap using a liquid bridge created between the chips. The parallel superhydrophobic surfaces do not require the addition of a gasket or other additional components so that the assembly process scales favorably with an increasing number of fluidic interconnects. The gasketless seal does not contribute to geometric constraint between the component chips which allows alignment between chips to scale favorably with an increasing number of fluidic ports and decouples chip-level alignment from the interconnect features. Two static analytical models were derived from the Young-Laplace equation to estimate the maximum steady-state pressure of the liquid at the liquid bridge. In the first model, the maximum pressure of the gasketless seal was a function of the surface tension of the liquid, the gap distance between the through-holes, and the static contact angle of the surfaces. The second generation model added the nominal lateral offset between the through-holes as a variable. Three sets of experiments were performed to evaluate performance of the gasketless interconnects. The first two demonstrated proof that the concept could work. The third set of experiments used injection molded chips with injection molded through-holes to ensure repeatable dimensions for the chips and locations of the through-holes. Chip-level alignment and gaps were defined by ball-in-v-groove kinematic alignment structures, with precision ground silicon nitride ball bearings used for the balls. A closed-loop pressure regulator was used to control the driving pressure of the fluid supplied by a pressurized liquid reservoir, and a pressure sensor to determine the pressure at the interconnect. The data validated the first generation model by showing that the model estimates of maximum interconnect pressures within ±50% of the measured maximum pressures for 76% of the samples. The measured maximum pressures did not match the second generation model. In fact, 67% of the pressure measurements were in the range of +150% to +7600% of the second generation model’s value. Further investigation should be performed to determine if the discrepancy was due to the assumption that a semicircular arc approximates the shape of the meniscus or the pressure sensor’s resolution. The gasketless seal withstands maximum pressures seen in microfluidic systems without adding additional kinematic constraints and is realizable within manufacturing variation. The first generation model can be used to estimate the required maximum pressure.

Date

2014

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Murphy, Michael C.

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