In this work, the investigator devises innovative computational methods for free surface microfluidics in order to understand and control absorption and evaporation processes in the sub-micron scale open channels, as well as to understand how to efficiently control the effect of surface tension and temperature profiles along the channels. In particular, efficient numerical schemes on adaptive meshes are constructed in order to address the multiscale nature of the problem and the limitations of computer resources. The investigator introduces a new paradigm that allows the discretization of PDEs on highly adaptive meshes as if the mesh was uniform, while attaining second-order accuracy in the maximum norm. The numerical simulations are used to supplement physical experiments in order to optimize the design of free surface fluidics devices. The simulations take into account the temperature field in the liquid and the surrounding channel walls, the temperature-induced variations in surface tension, the subsequent surface tension driven flows in the transversal direction of the main flow (Marangoni effect) and their effects on the transport of airborne particles from the surface of the liquid to its bulk. Furthermore, the simulations take the configuration of the whole air-liquid system into account and determine the shape of the free surface in order to find a design that maximizes contact between the air and the liquid surface for efficient capture of airborne species.
In the past 15 years, significant advances have been made in using micro/nanofluidic-based platforms for detecting chemical and biological agents. However, all the `lab-on-a-chip' platforms reported in the literature can process samples only after the samples are injected into a microchannel. This longstanding technological and scientific barrier limits the viability of these platforms for monitoring airborne species at time when the great importance of this technology to national security issues has become clear. Free-surface fluidics is an innovative technology pioneered by the investigator's collaborators at UCSB which removes this barrier by enabling previously impossible detection thresholds for certain trace airborne chemical agents and pathogens. Airborne molecules can be directly absorbed through the free surface, where they can interact with gold or silver colloidal particles and be detected using Surface-Enhanced Raman Spectroscopy. This platform could be used, for example, for public safety in a variety of venues to detect explosives and toxic chemicals, and for continuous monitoring of biological or chemical warfare agents in air ventilation systems. In this work, the investigator devises numerical methods in order to optimize the design of free-surface fluidic devices and to better understand the physical phenomena involved. These methods have an important impact on other fields as well, as they have key applications in the fields of semi-conductor processing and in the energy industry, in bio-nanotechnology and tissue engineering, in combustion as well as in the modeling of tumor growth to name a few. In addition, the investigator develops a freely available interactive web site on computational science and engineering which guides the users through a computational science journey, exploring intriguing topics such as microfluidics, crystal growth, single and multiphase flows. The users have the possibility of further interactive exploration by altering parameters to observe the effect on simulations, hence providing a tutorial on computational science.
