Enhanced thermal conductivity in polymer networks

Lyu, Guangxin

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https://hdl.handle.net/2142/115871 Copy

Description

Title

Enhanced thermal conductivity in polymer networks

Author(s)

Lyu, Guangxin

Issue Date

2022-07-01

Director of Research (if dissertation) or Advisor (if thesis)

• Cahill, David
• Evans, Christopher

Doctoral Committee Chair(s)

• Cahill, David
• Evans, Christopher

Committee Member(s)

• Braun, Paul
• Miljkovic, Nenad

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• thermal conductivity
• polymer
• dynamic polymer network
• time-domain thermoreflectance
• frequency-domain probe beam deflection
• crystal
• liquid crystal
• epoxy resin
• vitrimer

Abstract

This dissertation focuses on experimental studies of thermal transport in polymer networks, including the system of ‘epoxy resins’ and ‘vitrimers’, and designing the thermal conductivity of polymer network from molecular structure level. The thermal measurement is based on frequency-domain probe beam deflection (FD-PBD) and time-domain thermoreflectance (TDTR). Wide-angle X-ray scattering, Raman spectra, polarized optical microscope (POM), and differential scanning calorimetry (DSC) are used to characterize related properties of polymer. Discussion of heat transport of polymer network includes the concept from thermal physics, polymer physics, materials science, and chemistry. Polymer networks can be separated into 3 categories: amorphous polymer networks, crystalline polymer networks, and liquid crystalline polymer networks. Thermal conductivity ranges from 0.06 to 2.0 W/(m K) with variation of a factor of 30. Thermal conductivity of amorphous polymer networks ranges from 0.06 to 0.29 W/(m K). Thermal conductivity of amorphous polymer networks is strongly related to the mass density and has positive correlation with the speed of sound. In the polymer networks with similar molecular structure or amorphous vitrimer under different temperature, minimum thermal conductivity model (MTCM) well predicts the trend of the measured thermal conductivity. Thermal conductivity of crystal polymer network varies from 0.34 to 2.0 W/(m K). The variation in thermal conductivity comes from varied crystallinity and different crystal type. In a crystal ethylene-based vitrimer system with slow crystal progress up to 7 days, Wide-angle X-ray scattering (WAXS) and polarized optical microscopy (POM) were used to determine the changes in crystallinity with time. Raman spectroscopy, time-domain forced Brillouin scattering, and time-domain thermoreflectance (TDTR) measured temporal changes in chain conformation, elastic constants, and thermal conductivity. The quantitively correlation between crystallinity and thermal conductivity of this ethylene-based vitrimer is built between 0.10 to 1.0 W/(m K). In further design, crystal polymer network can have high thermal conductivity as 2.0 W/(m K), which is 10 times higher than common polymer. Liquid crystal structure can highly improve thermal conductivity of polymer network. In one epoxy resin system with similar structure, one epoxy resin with liquid crystal structure has thermal conductivity of 1.0 W/(m K) while another epoxy resin without liquid crystal structure only has thermal conductivity of 0.17 W/(m K) although they only have difference of one carbon in the molecular structure of monomer. A new method of molecular engineering based on dynamic covalent bond is raised and successfully improve the thermal conductivity of polymer network. The author is also known as Guangxin Lv.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Guangxin Lyu

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