<p>Recent
technological advances in the field of electronics and the accompanying trend
of device miniaturization with enhanced functionality has led to growing
interest in new methods of electronic device integration. As a result,
flexible, wearable, and portable electronic devices have emerged as a way of
providing a multifunctional infrastructure to facilitate various consumer
needs, creating new challenges for materials development. Polymers possess a
unique combination of desirable properties such as mechanical compliance,
durability, low density and chemical stability which makes them ideally
suitable as substrate materials to cater to such diverse applications. However,
the low thermal conductivity of polymers hinders their heat spreading
capability in thermal management applications for flexible and wearable
devices. In recent years, there has been a growing interest in ultra-high
molecular weight polyethylene (UHMW-PE) materials with aligned polymer chains
due to their remarkably high thermal conductivity that is similar to some
metals. These are commercially manufactured in large volumes as fibers using
gel-spinning and ultra-drawing processes that impart a high degree of
crystallinity and orientation to the polymer chains. As a result, these
materials develop exceptionally high mechanical strength, elastic modulus, and
thermal conductivity compared to conventional polymers. Therefore, UHMW-PE
materials have found applications in commercial products like motorcycle gear
and ballistic vests, but have not been commercially deployed for heat spreading
and thermal management applications. While there has been much fundamental work
on the development of high thermal conductivity fibers, effective translation
of the high conductivity from individual fibers to macroscale (wearable)
flexible fabrics has not been previously explored. The objective of this thesis
is to obtain a fundamental understanding of the thermal transport properties of
fabric materials constructed from the high conductivity polymer fibers, and assess
their applicability for potential heat spreading applications. </p>
<p>In the present
work, commercially available high thermal conductivity fibers made of UHMW-PE
are utilized to fabricate plain-weave fabrics prototypes, and the thermal
properties of individual fibers, yarns, and woven fabrics are measured using a
novel in-plane thermal measurement method. The characterization technique
leverages infrared (IR) microscopy for a non-contact temperature sensing and is
generally scalable for thermal characterization of the in-plane
thermal-conductivity of materials across different length scales. Effective
thermal conductivities on the order of ~10 Wm<sup>-1</sup>K<sup>-1</sup> are
achieved along the in-plane dominant heat transport direction of the woven
fabric, which is exceptionally high (~2-3 orders of magnitude) compared to
conventional clothing and textile-based materials. The thermal conductivity and
mechanical flexibility of the UHMW-PE fabrics are benchmarked with respect to
conventional materials and the effect of bend-stressing and thermal annealing
of the fabrics is characterization using the developed metrology. </p>
<p>Additionally, a
laser-based IR thermal metrology technique leveraging both non-contact heating
and temperature sensing is conceptualized and validated using a numerical
thermal modeling approach. The proposed technique provides an approach to
estimate the in-plane heat spreading properties of anisotropic materials with
direction-depended thermal properties based on quantifying the surface
temperature map of a sample subjected to periodic heating. Numerical
simulations are leveraged to demonstrate the applicability of this method to
enable measurement of a wide range of thermal properties indicating great
potential to develop this further as a standardized robust method for in-plane
anisotropic thermal characterization of materials such as fabrics and films.</p>
<p>This work sheds
light on the high thermal conductivity of UHMW-PE materials that can be
achieved using a scalable manufacturing process and describes the thermal metrology
approaches to enable their characterization, thereby providing a foundation for
the conceptualization and design of flexible substrate based thermal solutions
in future wearable/flexible electronic devices.</p>
<p> </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14191310 |
| Date | 16 March 2021 |
| Creators | Aaditya Candadai (10277555) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/THERMAL_METROLOGY_AND_CHARACTERIZATION_OF_HIGH_THERMAL_CONDUCTIVITY_POLYMER_FIBERS_AND_FABRICS/14191310 |
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