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Programmable Deformation of Liquid Crystal Elastomers.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Programmable Deformation of Liquid Crystal Elastomers./
Author:	Fowler, Hayden.
Description:	1 online resource (174 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-06, Section: B.
Contained By:	Dissertations Abstracts International85-06B.
Subject:	Chemical engineering. -
Online resource:	click for full text (PQDT)
ISBN:	9798381163339

Programmable Deformation of Liquid Crystal Elastomers.
Fowler, Hayden.

Programmable Deformation of Liquid Crystal Elastomers. - 1 online resource (174 pages)

Source: Dissertations Abstracts International, Volume: 85-06, Section: B.

Thesis (Ph.D.)--University of Colorado at Boulder, 2023.

Includes bibliographical references

This thesis investigates the programmable deformation of liquid crystal elastomers (LCEs) for directional electromechanical actuation and omnidirectional localized stretch. Focus is placed on developing LCEs for these functionalities through materials chemistry, processing, and properties adjustments. Through these adjustments, this work explores enhancing directional electromechanical deformation by improving the appropriate material properties (i.e., mechanical and dielectric) and enabling localization of deformation to omnidirectional stretch via processing of unaligned LCEs. The first part of this thesis primarily focuses on enhancing the magnitude, speed, and recovery of directional electromechanical deformation in LCEs. To this end, the first aim develops LCEs prepared from thiol-acrylate photopolymerizations with high Young's modulus contrast, low Young's modulus perpendicular to the alignment direction, and relatively high dielectric constant. The resulting materials accomplish uniaxial strains of up to 17.5% at 3.5 kV, demonstrating a marked improvement. Furthermore, LCEs respond and recover quickly, making them fully responsive to 1 Hz cycling frequency. The ability to align LCEs to photopatterned surfaces enables +1 azimuthal defect orientation, generating cone deformations on exposure to voltage. To further enhance deformation, the second aim prepares LCEs from thiol-ene photopolymerizations with tunable crosslinking. The first part of this aim explores the amenability of surface-enforced alignment and variation of crosslinker concentration to adjust material properties. Thiol-ene photopolymerization results in rapid network conversion, and materials are surface alignable, retaining the cybotactic nematic phase. While thermal and mechanical properties can be adjusted via crosslinking, decreasing crosslinker concentration results in the loss of Young's modulus contrast. LCEs are also explored for their thermomechanical response to investigate the role of cybotactic nematic phase behavior. In the second part of this aim, LCEs are prepared with an additional allyl ether functionalized liquid crystalline monomer while maintaining moderate crosslinker concentration. This coincidentally results in improved mechanical and dielectric properties, enhancing the directional electromechanical deformation. LCEs accomplish uniaxial strains of 28% at 4 kV and show improved speeds of deformation and recovery. As a result, residual strain accumulation over multiple cycles is significantly reduced.The second part of this thesis focuses on enabling localized deformations to omnidirectional stretch in LCEs via processing. To do this, the third and final aim prepares LCEs from thiol-acrylate photopolymerizations without macroscopic alignment (polydomain). By crosslinking in the precursor's isotropic or nematic state (referred to as isotropic and nematic genesis, respectively), the mechanical properties of LCEs are differentiated. A mask is used to pattern adjacent regions of isotropic or nematic genesis on a monolithic material, enabling patterning of mechanical properties without directionality. The resulting LCEs localize strain to the softer, isotropic genesis regions on deformation. Furthermore, the lack of directionality in the mechanical properties enables localization of omnidirectional stretch. Strain localization is predicted well by finite elements analysis simulations.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798381163339Subjects--Topical Terms:

555952
Chemical engineering.
Subjects--Index Terms:

Liquid crystal elastomersIndex Terms--Genre/Form:

554714
Electronic books.

Programmable Deformation of Liquid Crystal Elastomers.
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520 $a This thesis investigates the programmable deformation of liquid crystal elastomers (LCEs) for directional electromechanical actuation and omnidirectional localized stretch. Focus is placed on developing LCEs for these functionalities through materials chemistry, processing, and properties adjustments. Through these adjustments, this work explores enhancing directional electromechanical deformation by improving the appropriate material properties (i.e., mechanical and dielectric) and enabling localization of deformation to omnidirectional stretch via processing of unaligned LCEs. The first part of this thesis primarily focuses on enhancing the magnitude, speed, and recovery of directional electromechanical deformation in LCEs. To this end, the first aim develops LCEs prepared from thiol-acrylate photopolymerizations with high Young's modulus contrast, low Young's modulus perpendicular to the alignment direction, and relatively high dielectric constant. The resulting materials accomplish uniaxial strains of up to 17.5% at 3.5 kV, demonstrating a marked improvement. Furthermore, LCEs respond and recover quickly, making them fully responsive to 1 Hz cycling frequency. The ability to align LCEs to photopatterned surfaces enables +1 azimuthal defect orientation, generating cone deformations on exposure to voltage. To further enhance deformation, the second aim prepares LCEs from thiol-ene photopolymerizations with tunable crosslinking. The first part of this aim explores the amenability of surface-enforced alignment and variation of crosslinker concentration to adjust material properties. Thiol-ene photopolymerization results in rapid network conversion, and materials are surface alignable, retaining the cybotactic nematic phase. While thermal and mechanical properties can be adjusted via crosslinking, decreasing crosslinker concentration results in the loss of Young's modulus contrast. LCEs are also explored for their thermomechanical response to investigate the role of cybotactic nematic phase behavior. In the second part of this aim, LCEs are prepared with an additional allyl ether functionalized liquid crystalline monomer while maintaining moderate crosslinker concentration. This coincidentally results in improved mechanical and dielectric properties, enhancing the directional electromechanical deformation. LCEs accomplish uniaxial strains of 28% at 4 kV and show improved speeds of deformation and recovery. As a result, residual strain accumulation over multiple cycles is significantly reduced.The second part of this thesis focuses on enabling localized deformations to omnidirectional stretch in LCEs via processing. To do this, the third and final aim prepares LCEs from thiol-acrylate photopolymerizations without macroscopic alignment (polydomain). By crosslinking in the precursor's isotropic or nematic state (referred to as isotropic and nematic genesis, respectively), the mechanical properties of LCEs are differentiated. A mask is used to pattern adjacent regions of isotropic or nematic genesis on a monolithic material, enabling patterning of mechanical properties without directionality. The resulting LCEs localize strain to the softer, isotropic genesis regions on deformation. Furthermore, the lack of directionality in the mechanical properties enables localization of omnidirectional stretch. Strain localization is predicted well by finite elements analysis simulations.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2024
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653 $a Strain localization
653 $a Dielectric properties
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