Design of nematic liquid crystals to control microscale dynamics

Dynamics of small particles, both living such as swimming bacteria and inanimate, such as colloidal spheres, has fascinated scientists for centuries. If one could learn how to control and streamline their chaotic motion, that would open technological opportunities in areas such as the transformation of stored or environmental energy into systematic motion, micro-robotics, and transport of matter at the microscale. This overview presents an approach to command microscale dynamics by replacing an isotropic medium such as water with an anisotropic fluid, a nematic liquid crystal. Orientational order leads to new dynamic effects, such as propagation of particle-like solitary waves. Many of these effects are still awaiting their detailed mathematical description. By using plasmonic metamask photoalignment, the nematic director can be patterned into predesigned structures that control dynamics of inanimate particles through the liquid crystal enabled nonlinear electrokinetics. Moreover, plasmonic patterning of liquid crystals allows one to command the dynamics of swimming bacteria, guiding their trajectories, polarity of swimming, and concentration in space. The patterned director design can also be extended to liquid crystal elastomers, in which case the director gradients define the dynamic profile of elastomer coatings. Some of these systems form an experimental playground for the exploration of out-of-equilibrium active matter, in which the levels of activity, degree of orientational order and patterns of alignment can all be controlled independently of each other.Comment: 35 pages, 9 figures, a review based on a lectur

Electrokinetic Phenomena and Singularity-Driven Flows in Nematic Liquid Crystals

University of Minnesota Ph.D. dissertation. November 2017. Major: Physics. Advisor: Jorge Vinals. 1 computer file (PDF); ix, 165 pages.Electrokinetic phenomena, including electrophoresis and electroosmosis, provide a significant tool for engineering the transport of fluids and particles at microscopic scales. This thesis describes additional mechanisms for generating electrokinetic flow by using a nematic liquid crystal electrolyte. Under an applied electric field the anisotropic properties of the liquid crystal lead to separation of ionic impurities present in the fluid, which couple with the applied field to produce electrostatic forces that drive fluid and particle motion. This force is quadratic in the electric field, implying that systematic flow occurs even in the presence of an oscillating field. This thesis presents numerical and analytical investigations of this electrokinetic mechanism. We show that the charge density and fluid velocity of a system depends strongly on the topology of the liquid crystal orientation, and we present results for several distinct configurations, including periodic distortions, isolated disclinations, and particle suspensions. We also show that liquid crystal electrokinetic systems can be designed to mimic the behaviors of active nematics – collections of particles which can self-propel along a particular direction

A Hybrid Microfluidic Chip with Multielectrode Geometry for Cell Concentration using AC pDEP and Multiwave ACEOF

Microfluidic systems for cell concentration are becoming increasingly important tools in life science research and diagnostics. The ability to handle life cells in a highly controlled environment offers opportunities to automate complex procedure such as IVF, liquid biopsy, and single-cell isolation. Despite promising applications, present-day cell isolation techniques, either lag efficiency or deal with specific cells only. On the other hand, AC Electroosmotic flow (ACEOF) apply force on fluid medium only and therefore does not rely on cell properties. From this point of view, AC EOF is an exciting alternative for current cell concentration techniques. This research combines two AC Electrokinetic phenomena, namely AC positive dielectrophoresis (AC pDEP) and AC Electroosmotic flow (ACEOF), to build a microfluidic device that is capable of providing a cell concentration factor of 100000/mL at the flow rate of 45μL/min. To achieve this goal, firstly, AC pDEP and ACEOF response are thoroughly examined against the parameters such as electrode geometry, interelectrode gap, fluid conductivity, chamber height, AC signal strength and frequency, and it is established that 75μm interelectrode gap provide an ACEOF vortex size of 430μm at 10Vpp, 1kHz for the fluid conductivity of 10mS/m while 100μm interelectrode gap provides a vortex size of 290μm for the same parameters. On the other hand, 20Vpp, 1MHz provides AC pDEP efficiency of ~50% at 300μm chamber height for a pair of electrodes. Based on these results, a microfluidic device is built with ten individually addressable electrodes, which offers an AC pDEP efficiency of >95% at 45μl/min flow rate, with overall ACEOF yield of >90% and an concentration factor of 100000 using 2000s AC pDEP and five waves of ACEOF. In the end, results of both AC pDEP and ACEOF are validated using finite element modelling that also provides a model for multi-vortex ACEOF

Microgravity Science and Applications. Program Tasks and Bibliography for FY 1993

An annual report published by the Microgravity Science and Applications Division (MSAD) of NASA is presented. It represents a compilation of the Division's currently-funded ground, flight and Advanced Technology Development tasks. An overview and progress report for these tasks, including progress reports by principal investigators selected from the academic, industry and government communities, are provided. The document includes a listing of new bibliographic data provided by the principal investigators to reflect the dissemination of research data during FY 1993 via publications and presentations. The document also includes division research metrics and an index of the funded investigators. The document contains three sections and three appendices: Section 1 includes an introduction and metrics data, Section 2 is a compilation of the task reports in an order representative of its ground, flight or ATD status and the science discipline it represents, and Section 3 is the bibliography. The three appendices, in the order of presentation, are: Appendix A - a microgravity science acronym list, Appendix B - a list of guest investigators associated with a biotechnology task, and Appendix C - an index of the currently funded principal investigators

Early growth technology analysis : case studies in solar energy and geothermal energy

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 85-87).Public and private organizations try to forecast the future of technological developments and allocate funds accordingly. Based on our interviews with experts from MIT's Entrepreneurship Center, Sloan School of Management, and IBM, and review of literature, we found out that this important fund allocation process is dominated by reliance on expert opinions, which has important drawbacks alongside its advantages. In this Thesis, we introduce a data-driven approach, called early growth technology analysis, to technology forecasting that utilizes diverse information sources to analyze the evolution of promising new technologies. Our approach is based on bibliometric analysis, consisting of three key steps: extraction of related keywords from online publication databases, determining the occurrence frequencies of these keywords, and identifying those exhibiting rapid growth. Our proposal goes beyond the theoretical level, and is embodied in software that collects the required inputs from the user through a visual interface, extracts data from web sites on the fly, performs an analysis on the collected data, and displays the results. Compared to earlier software within our group, the new interface offers a much improved user experience in performing the analysis. Although these methods are applicable to any domain of study, this Thesis presents results from case studies on the fields of solar and geothermal energy. We identified emerging technologies in these specific fields to test the viability of our results. We believe that data-driven approaches, such as the one proposed in this Thesis, will increasingly be used by policy makers to complement, verify, and validate expert opinions in mapping practical goals into basic/applied research areas and coming up with technology investment decisions.by Ayse Kaya Firat.S.M.in Technology and Polic