PhD Oral Exam - Angel Perez-Cruz, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Over the past few years, paper-based microfluidics systems have been extensively applied to perform different analytical tasks including detection and quantification of the specific analyte. Few works have reported the use of paper as a structural element to develop both sensors and actuators. These devices are extremely useful as they are inexpensive, easy to fabricate, disposable and portable. However, other features of paper that can be applied to develop new sensors have not been explored. Paper is a hygroscopic material that enables the generation of motion by hygromorphism.

In this work, paper-based hygro-mechanical systems (PB-HMS) for liquid characterization are developed. The configuration of the developed PB-HMS is formed by the interaction of a paper-based cantilever beam and a liquid droplet. The paper-based cantilever beam acts as a hygroscopic sensitive element, while the liquid droplet triggered the bending response of the PB-HMS. These systems do not require any external source of energy to stimulate the sensing element (i.e. electric or magnetic field) as its interaction with the liquid droplet activates the motion.

In addition, different gaps in the knowledge found in the open literature were addressed to develop the PB-HMS sensor. First, an imbibition model based on Richards’ equation, is developed in this thesis to predict liquid imbibition in complex paper-based networks. Second, a dimensionless stress-imbibition model including three main nonlinearities (imbibition, swelling and softening) is developed in this work. Third, the influences of such nonlinearities on the characteristic hygro-mechanical bending response of paper-based beams are studied. Fourth, the design of the PB-HMS is performed in order to extract information from the systems using their dynamic response. Finally, a method to quantify the dynamic performance of the PB-HMS in order to characterize liquid is developed.