Announcements

Title: Additive Manufacturing of Microfluidic Technologies via In Situ Direct Laser Writing

Day/Time: Thursday Feb 11th 2021, 10:45am-12:45pm

Examining Committee:
Ryan Sochol (Chair)
Don DeVoe
Eleonora Tubaldi
Axel Krieger
Reza Ghodssi (Dean’s Represenative)

Abstract: Innovations in microfluidic technologies hold great promise for a wide range of chemical, biomedical, and soft robotic applications. Unfortunately, key drawbacks associated with soft lithography-based microfabrication processes hinder such progress. To address these challenges, we advance a novel submicron-scale additive manufacturing (AM) strategy, termed “in situ direct laser writing (isDLW)”. IsDLW is an approach that benefits from the architectural versatility and length scales inherent to two-photon polymerization (2PP), while simultaneously supporting the micro-to-macro interfaces required for its effective utilization in microfluidic applications. In this dissertation, we explore isDLW strategies that enable passive and active 3D microfluidic technologies capable of enhancing “on-chip” autonomy and sophistication. Initially, we use poly(dimethylsiloxane) (PDMS)-based isDLW to fabricate microfluidic diodes that enable unidirectional rectification of fluid flow. We introduce a novel cyclic olefin polymer (COP)-based isDLW strategy to address several limitations related to structural adhesion and compatibility of PDMS microchannels. We use this COP-based approach to print microfluidic transistors comprising flexible and free-floating components that enable both “normally open” (NO) and “normally closed” (NC) functionalities—i.e., source-to-drain fluid flow (Q_SD) through the transistor is either permitted (NC) or obstructed (NO) when a gate input (P_G) is applied. As an exemplar, we employ COP-based isDLW to print an integrated microfluidic circuit (IMC) comprised of soft microgrippers downstream of NC microfluidic transistors with distinct P_G thresholds. All of these microfluidic circuit elements are printed within microchannels ≤40 μm in height, representing the smallest such components (to our knowledge). Theoretical and experimental results illustrate the operational efficacy of these components as well as characterize their performance at different input conditions, while IMC experimental results demonstrate sequential actuation of the microrobotic components to realize target gripper operations with a single P_G input. Furthermore, to investigate the utility of this strategy for static microfluidic technologies, we fabricate: (i) interwoven bioinspired microvessels (inner diameters<10μm) capable of effective isolation of distinct microfluidic flow streams, and (ii) deterministic lateral displacement (DLD) microstructures that enable continuous sorting of submicron particles (860 nm). In combination, these results suggest that the developed AM strategies offer a promising pathway for advancing state-of-the-art microfluidic technologies for various biological and soft robotic applications

Title: ADVANCED ABSORPTION MATERIALS AND THEIR APPLICATION IN REFREGIATION

Date/Time: January 12, 2021 2:00PM – 4:00PM

Committee:
Prof. Bao Yang (Chair)
Prof. Amir Riaz
Prof. Peter B. Sunderland
Prof. Teng Li
Prof. Chunsheng Wang (Dean Representative).

Zoom Link: https://umd.zoom.us/j/94210112455?pwd=MjVWRS9TVXR4cENFb2t3aTlTR0ljUT09

Abstract: Absorption chillers, which utilize heat as the primary energy input, have been considered a more environment-friendly alternative to vapor-compression cooling systems. The thermodynamic properties of absorbent generally limit the performances of absorption chillers. In the first part of the dissertation, a new method to determine the molecular interaction energies is developed. The molecular interaction energies can be related to many macroscopic thermodynamic properties, such as desorption heat and hygroscopicity. From the studies on ionic liquid absorbents, it is found that a shorter alkyl group in anion would produce higher interaction energy with water, thus increasing the hygroscopicity. In contrast, the fluorination of anion would reduce its interaction energy with water, thus reducing the hygroscopicity. A new formula is also developed using interaction energies to predict the desorption heat of absorbents, which is an essential parameter for evaluating absorbent performances. The second part of the dissertation focuses on the development of a microemulsion-based absorption chiller consisting of an electrostatic desorber, a nozzle-based absorber and an evaporator. Due to the tiny droplet size, it is thermodynamically challenging to regenerate the absorbed water in a liquid form from a microemulsion state. The electrostatic desorber would first utilize heat to transform the microemulsion absorbent into a macroemulsion state. The voltage is then applied to the absorbent to expedite the regeneration. Therefore, the electrostatic desorber can regenerate the absorbed water in a liquid form, which eliminates the latent heat requirement, offering the potential to improve energy efficiency. Inspired by the honeycomb shape, electrodes in the desorber are arranged in a multi-hexagon pattern, enabling a large desorber volume without increasing the voltage amplitude. The potential cooling power is improved by over 50 times compared to the original single-electrode desorber. The nozzle-based absorber&evaporator system utilizes nozzles to generate microemulsion absorbent and water in small droplet size to enhance the absorption and evaporating process.  Combining the electrostatic desorber and the absorber&evaporator system, the complete absorption chiller could run continuously and achieve a cooling power of about 100 W.