Award Date

12-1-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Kwang Kim

Second Committee Member

Woosoon Yim

Third Committee Member

Brendan O'Toole

Fourth Committee Member

Jaeyun Moon

Fifth Committee Member

Jee Woong Park

Number of Pages

247

Abstract

Polyvinyl chloride (PVC) gels are an electroactive polymer smart material which has been considered in a variety of actuator applications. Their large deformation, fast response rates, optical transparency, and soft nature has made them a key area of interest in fields ranging from soft robotics to optics. PVC gels are made from PVC mixed with large quantities of plasticizer, such as dibutyl adipate (DBA). When a voltage is applied, the gel experiences an “anodophilic” deformation (in which it moves preferentially towards the anode). This unique characteristic is the result of a charge buildup near the anode surface, which creates electromechanical transduction. This allows for PVC gels to be used as varifocal lenses, contraction actuators, bending actuators, and vibrotactile haptic feedback actuators, many of which are not possible using other smart materials. A large mechanoelectrical effect (where a mechanical deformation produces a voltage response) has also been found in PVC gels, allowing them to be used as pliable sensors without the need for external amplification.

While the applications of PVC gels in a variety of actuator types have been thoroughly documented, the fundamental mechanism for gel actuation is still poorly understood. This presents a challenge in the design and prediction of actuator performance, as well as material improvement. Additionally, while operating at lower voltages than other smart materials, such as dielectric elastomers, PVC gels still require higher voltages and offer lower force output than are acceptable for many applications. This work seeks to work towards a remedy of these problems in the field.

Herein, a theoretical and experimental investigation of the electromechanical actuation properties of PVC gels is undertaken. The focus of this work is primarily on the mechanism of PVC gel actuation, and key parameters for performance improvement in actuator applications. The PVC gels’ electrical, thermal, and mechanical properties along with their electromechanical response as actuators are characterized. The electrode polarization process in PVC gels is fit using a Debye relaxation model, and the conduction mechanism in PVC gels is identified as a correlated barrier hopping process. The actuation of PVC gels undergoing a cyclic linear voltage sweep is shown to display a current peak that occurred simultaneously with the onset of mechanical actuation. This is used as a novel characterization method to determine the total space charge present within the gel based upon the polarization from the integrated current.

To address the concern of a lack of control and prediction of actuation, a finite element analysis model of the electrostatic actuation of PVC gels is created. The model primarily focuses on two common actuator geometries: mesh and parallel plate contraction actuators. A parametric study is performed to determine the effects of the anode mesh size, Young’s modulus, and gel thickness on the actuation. To verify the model, the simulations’ displacement response is compared to PVC gel actuators that are fabricated and tested in contraction at various voltages. The results indicate that the model is in good agreement with the experimental results of PVC gel actuation and is capable of an acceptable prediction of the gel response. This model furthers the understanding of the most important parameters for PVC gel actuators, is useful in optimization, and could be applied in the future development of novel actuator geometries.

In the final studies described here, we produce an improved actuator via the incorporation of functionalized graphene oxide. Graphene oxide was found to increase the performance of the gels dramatically, improving displacement (20%), force production (41%), and power output (36%). The mechanism of performance enhancement of PVC gel actuators through the use of conductive fillers is clarified. PVC gels with functionalized carbon nanotubes (CNTs) and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) ionic liquid additives are fabricated to study their electrical and mechanical properties, and how they differ in terms of their ability to create more functional PVC gel actuators. A recommendation is made for additives in distinct applications, and the work opens the door for additional exploration into the area.

Keywords

Actuator; Electroactive polymer; PVC gel; Smart material

Disciplines

Engineering Science and Materials | Materials Science and Engineering | Mechanical Engineering

File Format

pdf

File Size

7800 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

Available for download on Thursday, December 15, 2022


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