Development of Ion Conducting Polymer Temperature Sensors

Citation

Higdon, Nicole Juliet (2026) Development of Ion Conducting Polymer Temperature Sensors. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/avyc-pq77. https://resolver.caltech.edu/CaltechTHESIS:06132025-183938139

Abstract

Improvements to flexible polymer temperature sensors have the potential to substantially improve human health through a variety of devices such as core body temperature sensors, temperature mapping, and IR imaging. In this thesis we examine a novel resistive ion conducting polymer-based temperature sensitive material. This material outperforms vanadium oxide and other leading temperature sensing materials for the temperature range 15-65 °C allowing for high performance use in medical devices. Unlike conventional materials, this polymer can be readily integrated into flexible devices.

In this thesis we explore both the fundamental science and applications of this material. In Chapter 2 of this thesis, we explore the electrical and chemical properties of this polymer through impedance spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. We explore the formation of interpolymer complexes exhibited by this copolymer. We demonstrate its application to temperature mapping and infrared light detection. Chapter 3 explores the effects of water on ion transport within the polymer. Demonstrating that the metal cation is the charge carrier, and that water uptakes primary effect is the lowering of the polymers’ glass transition temperature. Through visible spectroscopy we additionally demonstrate tetrahalocobaltate formation in this and a related polymer. In Chapter 4, we demonstrate an ultra-thin dual heat flux core body temperature sensor leveraging this polymer. We evaluate its response time then verify its functionality by leveraging an agar tissue phantom. We explore the formation of thin film sensors in Chapter 5. We demonstrate a simple sensor with a thin film architecture and discuss in depth the engineering challenges presented by commercialization of this architecture in the context of roll-to-roll fabrication. We demonstrate the sensor is strongly affected by external humidity and develop and demonstrate humidity buffer materials inspired by humidity fixed point salt solutions to address this problem.

In conclusion this thesis provides a window into the mechanism of a novel temperature sensing polymer and explores its commercialization and future applications.

Thesis Files