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Liquid Crystal Electrorheological Fluids in Geometrically Patterned Microvalves /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Liquid Crystal Electrorheological Fluids in Geometrically Patterned Microvalves // Chastity Kelly.
Author:	Kelly, Chastity,
Description:	1 electronic resource (127 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 86-11, Section: B.
Contained By:	Dissertations Abstracts International86-11B.
Subject:	Mechanical engineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31995103
ISBN:	9798314844625

Liquid Crystal Electrorheological Fluids in Geometrically Patterned Microvalves /
Kelly, Chastity,

Liquid Crystal Electrorheological Fluids in Geometrically Patterned Microvalves /Chastity Kelly. - 1 electronic resource (127 pages)

Source: Dissertations Abstracts International, Volume: 86-11, Section: B.

This dissertation presents the design, fabrication, and characterization of liquid crystal-based electrorheological (ER) valves with non-flat topography patterned into the electrode surfaces. The work is motivated by the need for compact control of soft robotic systems, for example for bench-top models that accurately simulate the dynamic motions of the gastrointestinal (GI) tract for testing ingestible medical devices. Although liquid crystal electrorheological valves with flat electrodes have previously been demonstrated for flow control, this dissertation represents the first examination of the effects of non-flat electrodes and the electric field concentrations that they induce on the valves' effectiveness at modulating flows under an applied electric field. In developing a family of liquid crystal ER valves that modulate hydraulic actuation at lower voltage and electric field than conventional ER valves with flat electrodes do, the study also uncovers key insights into the physical behavior of these systems, including how valve geometry and the inclusion of dopants affect the valves' electrorheological response. The research provides new knowledge that can lay the groundwork for future development and control of soft robotic actuators.The focus of the research is on ER valves with non-flat electrode topography that use liquid crystals as the active electrorheological fluid. The reversible change in viscosity induced by an applied electric field in these valves is exploited to achieve rapid flow modulation at lower values of applied voltage and electric field than are obtained in typical flat-electrode, liquid crystal electrorheological valves. The actuation and modulation effectiveness of both pure and doped liquid crystals in both flat and non-flat valves is investigated, with particular attention paid to the influence of valve geometry, flow rate, and electrical stimulus on the viscosity response. The work hypothesizes that the incorporation of dopants can alter both the length scale over which a given liquid crystal orientation is maintained at zero electric field and the mechanisms through which applied electric fields can induce increases in apparent viscosity in the system.A combination of experimental measurements, analytical modeling, numerical modeling, and statistical analysis techniques is used to evaluate valve performance. The analytical models, based on the Hagen-Poiseuille equation and torque balance formulations, provide a framework for understanding the flow dynamics and director reorientation under applied electric fields. Numerical models offer insight into the tradeoffs among various valve geometries, while parameter estimation methods refine the model parameters by incorporating experimental data, enabling quantitative predictions of valve performance across different operating conditions.The results indicate that geometrically patterned valves outperform flat valve designs, as evidenced by larger viscosity increases under equivalent electric field and equivalent flow rate and shear rate conditions. Additionally, the doped liquid crystals exhibit enhanced electrorheological effects relative to their pure counterparts, a result attributed to a combined effect of altered free energy state and a dielectrophoretic effect. These findings advance the fundamental understanding of ER fluid behavior in nematic liquid crystals as a function of the geometry of the space in which they are constrained and lay the groundwork for future development of actuators based on this type of valve. In conclusion, this dissertation demonstrates that an integrated approach-combining experimental techniques with analytical and statistical modeling-can effectively characterize the complex interactions governing ER valve performance. The results demonstrate that non-flat valve geometries can enhance flow modulation at given applied voltage and electric field and suggests directions for future research into the interplay between dopants, valve geometry, and electrorheological behavior.

English

ISBN: 9798314844625Subjects--Topical Terms:

649730
Mechanical engineering.
Subjects--Index Terms:

Electrorheology

Liquid Crystal Electrorheological Fluids in Geometrically Patterned Microvalves /
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520 $a This dissertation presents the design, fabrication, and characterization of liquid crystal-based electrorheological (ER) valves with non-flat topography patterned into the electrode surfaces. The work is motivated by the need for compact control of soft robotic systems, for example for bench-top models that accurately simulate the dynamic motions of the gastrointestinal (GI) tract for testing ingestible medical devices. Although liquid crystal electrorheological valves with flat electrodes have previously been demonstrated for flow control, this dissertation represents the first examination of the effects of non-flat electrodes and the electric field concentrations that they induce on the valves' effectiveness at modulating flows under an applied electric field. In developing a family of liquid crystal ER valves that modulate hydraulic actuation at lower voltage and electric field than conventional ER valves with flat electrodes do, the study also uncovers key insights into the physical behavior of these systems, including how valve geometry and the inclusion of dopants affect the valves' electrorheological response. The research provides new knowledge that can lay the groundwork for future development and control of soft robotic actuators.The focus of the research is on ER valves with non-flat electrode topography that use liquid crystals as the active electrorheological fluid. The reversible change in viscosity induced by an applied electric field in these valves is exploited to achieve rapid flow modulation at lower values of applied voltage and electric field than are obtained in typical flat-electrode, liquid crystal electrorheological valves. The actuation and modulation effectiveness of both pure and doped liquid crystals in both flat and non-flat valves is investigated, with particular attention paid to the influence of valve geometry, flow rate, and electrical stimulus on the viscosity response. The work hypothesizes that the incorporation of dopants can alter both the length scale over which a given liquid crystal orientation is maintained at zero electric field and the mechanisms through which applied electric fields can induce increases in apparent viscosity in the system.A combination of experimental measurements, analytical modeling, numerical modeling, and statistical analysis techniques is used to evaluate valve performance. The analytical models, based on the Hagen-Poiseuille equation and torque balance formulations, provide a framework for understanding the flow dynamics and director reorientation under applied electric fields. Numerical models offer insight into the tradeoffs among various valve geometries, while parameter estimation methods refine the model parameters by incorporating experimental data, enabling quantitative predictions of valve performance across different operating conditions.The results indicate that geometrically patterned valves outperform flat valve designs, as evidenced by larger viscosity increases under equivalent electric field and equivalent flow rate and shear rate conditions. Additionally, the doped liquid crystals exhibit enhanced electrorheological effects relative to their pure counterparts, a result attributed to a combined effect of altered free energy state and a dielectrophoretic effect. These findings advance the fundamental understanding of ER fluid behavior in nematic liquid crystals as a function of the geometry of the space in which they are constrained and lay the groundwork for future development of actuators based on this type of valve. In conclusion, this dissertation demonstrates that an integrated approach-combining experimental techniques with analytical and statistical modeling-can effectively characterize the complex interactions governing ER valve performance. The results demonstrate that non-flat valve geometries can enhance flow modulation at given applied voltage and electric field and suggests directions for future research into the interplay between dopants, valve geometry, and electrorheological behavior.
546 $a English
590 $a School code: 0160
650 4 $a Mechanical engineering. $3 649730
650 4 $a Applied physics. $3 3343996
650 4 $a Biomedical engineering. $3 535387
650 4 $a Fluid mechanics. $3 528155
653 $a Electrorheology
653 $a Liquid crystals
653 $a Microvalves
653 $a Electrorheological fluid
653 $a Gastrointestinal tract
690 $a 0548
690 $a 0541
690 $a 0215
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710 2 $a Northeastern University. $b Mechanical and Industrial Engineering. $e degree granting institution. $3 3816340
720 1 $a Livermore, Carol $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 86-11B.
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791 $a Ph.D.
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