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Ion Transport in Temperature Sensitive Polyelectrolytes


Wang, Linghui (2023) Ion Transport in Temperature Sensitive Polyelectrolytes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/zsat-9s73.


Temperature sensors are widely employed and play a key role in many industries, such as automotive vehicles, medical devices, environmental monitoring, and process control. The state-of-the-art thermal sensing elements are made of rigid and costly inorganic materials, such as vanadium oxide and platinum. These materials have limitations for emerging applications such as wearable devices and prosthetic devices. Ideal temperature sensing materials for such applications need to be flexible, reliable under mechanical deformation, and suitable for large-area production. Electrical conductive polymers were found to be a promising solution because of their flexibility and solution processability. However, they often lag in temperature resolution compared to their inorganic counterparts.

A recent discovery revealed that the ionic conductivity of crosslinked pectin, a biopolymer extracted from plant cell walls, has a record-high temperature response. It is biocompatible, flexible when hydrated, and solution-processable, making it a strong candidate for wearable temperature sensing and conformal temperature mapping. However, open questions remain about the origin of its temperature sensitivity and the principles governing its ion transport. Furthermore, the heterogeneity of the complex molecular structure of pectin presents challenges to its integration in sensing devices.

In this thesis, we study the origin of the high thermal sensitivity in pectin and develop a synthetic polyelectrolyte that mimics its key structure and properties. In Chapter 3, we focus on the ion transport mechanism in crosslinked pectin. We show that the binding between multivalent ions and certain chemical functional groups of pectin plays a critical role in its temperature sensitivity. In Chapter 4, the impact of water content on the ion transport and dielectric processes in crosslinked pectin is also investigated. In the following chapter, we present a novel synthetic polyelectrolyte designed to mimic pectin with a simpler structure. It has superior flexibility, high temperature sensitivity, and is stable under mechanical deformation. To further study this new material, we examine its ion transport dynamics under varying humidity and temperature conditions in Chapter 7. We discover that temperature and humidity have a similar effect on ion transport. Overall, we showed a biomimetic approach to design temperature sensitive polymers where the strong ion-polymer binding is the key to the ultrahigh temperature response.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:ion transport; polyelectrolytes;thermally-responsive polymers; ion-conducting polymers
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Daraio, Chiara
Thesis Committee:
  • Minnich, Austin J. (chair)
  • Wang, Zhen-Gang
  • Bernardi, Marco
  • Daraio, Chiara
Defense Date:22 February 2023
Funding AgencyGrant Number
Samsung Electronics Company, Ltd.SAMS.2016GRO
Heritage Medical Research Institute (HMRI)HMRI-15-09-01
DelWebb FoundationUNSPECIFIED
Schwartz-Reisman Collaborative Science ProgramUNSPECIFIED
NSF Center to Stream Healthcare in PlaceUNSPECIFIED
Record Number:CaltechTHESIS:05142023-192053975
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 5
Wang, Linghui0000-0003-2492-7364
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15170
Deposited By: Linghui Wang
Deposited On:16 May 2023 16:18
Last Modified:08 Nov 2023 00:21

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