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Title:Rapid on-demand polymerization for multifunctional materials
Author(s):Dean, Leon M
Director of Research:Sottos, Nancy R
Doctoral Committee Chair(s):Sottos, Nancy R
Doctoral Committee Member(s):Moore, Jeffrey S; Evans, Christopher M; Chen, Qian
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Multifunctional materials
frontal polymerization
shape memory polymers
3D printing
Abstract:Multifunctional materials are able to perform multiple functions through judicious combinations of structural and non-structural properties, leading to enhancements in systems-level performance. Because multifunctional materials are inherently complex, their manufacturing is typically expensive and difficult to scale up. Frontal polymerization (FP) has emerged as a rapid, energy-efficient, and easily scalable manufacturing technique for bulk polymeric materials, with significant potential to ease the manufacturing burdens of multifunctional polymer and composite materials. In FP, monomer is converted into polymer within a localized reaction zone (i.e. front) that self-propagates due to the diffusion of heat released by the exothermic polymerization. Recently, frontal ring-opening metathesis polymerization (FROMP) has attracted attention for the production of high-performance materials. Prior FROMP studies focused exclusively on dicyclopentadiene (DCPD) and other norbornene-based monomers, which produce rigid polymers suitable for structural applications. This dissertation describes advances in FROMP which enable the production of a wide range of materials, including elastomers, shape memory polymers, nanocomposites, and patterned materials, with an emphasis on multifunctionality. The production of elastomers and shape memory polymers is enabled by the introduction of 1,5-cyclooctadiene (COD) as a novel FROMP monomer. Although the ring strain of COD is less than DCPD, the heat released by homopolymerization of COD is sufficient to sustain front propagation with a velocity suitable for time-efficient manufacturing (ca. 0.6 mm/s). Furthermore, FROMP copolymerization of COD and DCPD produces crosslinked polymers with widely tunable properties, including glass transition temperature (Tg) varying over a range of ca. 200 °C, tensile modulus varying over 3 orders of magnitude, and tensile strength varying 40-fold. Robust elastomeric behavior is demonstrated for copolymers with Tg below room temperature, and multistage shape memory actuation is demonstrated for copolymers with Tg above room temperature. Polymer nanocomposites are prepared by incorporating nanoparticles into DCPD and COD-DCPD resins prior to FROMP. Light-absorbing carbon nanoparticles, which efficiently convert energy from light into heat, are utilized for non-contact photothermal initiation of FROMP. The addition of 1 wt% carbon black results in a 30-fold decrease in the energy input required for photothermal initiation compared to neat DCPD resin. Furthermore, higher loadings of silica and carbon nanoparticles are utilized to control rheological properties for layer-by-layer and freeform 3D printing. The 3D printed parts are rapidly cured (<1 min) in ambient conditions via FROMP. Carbon nanoparticles also enable the printing of electrically conductive nanocomposites with strain sensing functionality. Patterned materials are prepared via a bioinspired stress-induced patterning technique. Static and dynamic mechanical inputs are imposed on partially cured DCPD gels during FROMP. Well-controlled surface topography patterns are created by imposing dynamic mechanical inputs on neat DCPD gels. Short fiber composites with tailored fiber orientation and mechanical properties are created by imposing static mechanical inputs on fiber-containing gels. Finally, in an ostensibly unrelated area of research, microvascular materials with self-healing functionality are investigated. Segmented gas-liquid flow is used to deliver self-healing reagents through internal microvasculature to large-scale damage, leading to improvements in mixing and healing performance compared to alternative delivery strategies. Although the microvascular materials described herein are fabricated via conventional curing techniques, we envision that FP-based approaches could be used to efficiently fabricate future generations of microvascular self-healing materials.
Issue Date:2021-01-19
Rights Information:Copyright 2021 Leon M. Dean
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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