Evolution of material properties in patterned semi-crystalline structures enabled by frontal polymerization

Rodriguez Koett, Luis Enrique

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https://hdl.handle.net/2142/127350 Copy

Description

Title

Evolution of material properties in patterned semi-crystalline structures enabled by frontal polymerization

Author(s)

Rodriguez Koett, Luis Enrique

Issue Date

2024-11-20

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

Sottos, Nancy R

Doctoral Committee Chair(s)

Sottos, Nancy R

Committee Member(s)

• Geubelle, Philippe
• Schroeder, Charles M
• Leal, Cecilia

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)

• frontal polymerization
• patterned structures
• hierarchical materials
• fracture
• polymers
• dicyclopentadiene
• cyclooctadiene
• instabilities
• patterning

Abstract

Natural systems produce materials with hierarchical structures, many of which contain examples of disparate, patterned domains that lead to superior mechanical performance. Much of the work to date has used additive manufacturing techniques to achieve hierarchical bio-inspired structures. Unfortunately, one pitfall of many 3D printing approaches is the need for manual intervention and post-curing processes to achieve the final structures. Frontal polymerization (FP) is a rapid, energy-efficient thermosetting polymer manufacturing technique facilitated by a thermally latent initiator which triggers a self-sustaining curing front. FP can generate complex and free-form structures at a fraction of the energy and capital costs while simultaneously producing materials at a much higher rate. The dynamics of the propagating front that rapidly converts the liquid monomers into solid polymers are tuned using chemical and experimental parameters to achieve non-planar behavior. This non-planar behavior leads to the creation of disparate material domains. In particular, the FP of 1,5-cyclooctadiene (COD) creates semi-crystalline polymers that have both soft (amorphous) and stiff (crystalline) domains. This dissertation describes the systematic characterization of COD-based co-polymers material properties and studies the effect of having these disparate material domains on the mechanical performance of the material. Remarkably, small changes in the initiator structure resulted in significant variation of mechanical performance and preferred polymer chain orientation for the three systems studied. Ru-1 is found to yield the toughest co-polymers with strain energy densities that are at least three times greater than Ru-2 and Ru-3 initiated structures. In contrast, Ru-3 leads to the strongest and stiffest patterned structures. This initiator also leads to anisotropic mechanical properties in patterned systems. The patterned Ru-3 system retains the properties achieved for its uniform counterpart in the P2 direction while being an overall tougher structure. The mechanical performance of these patterned structures is further tuned by adjusting the size of the semi-crystalline and amorphous domains showcasing a greater range of properties. Interestingly, the properties of these systems are not constant and evolve significantly as the structures age. We evaluated the temporal evolution of material properties in patterned COD-based co-polymers initiated with the Ru-1 and Ru-3 initiators. Both Ru-1 and Ru-3 systems exhibit significant crystallinity and mechanical property variation over a two-week aging period. The large property fluctuations observed are attributed to the active initiator remaining post-polymerization and its ability to induce chain transfer events along the polymer backbone. Changes in relative crystallinity are found to be correlated better with changes in strength than modulus or strain energy density for all the systems tested. We further explored the fracture toughness of these patterned systems through the characterization of the work of fracture in a double-edge notched tension (DEN(T)) test using the essential work of fracture theory. The use of this theory allows the differentiation between the work that goes into growing a crack and the work that goes into a diffuse zone around the crack propagation path where most of the plastic deformation occurs. Ru-1 samples which contain patterned domains are found to be at least 160% tougher than uniform samples regardless of the alignment of the domains. The toughness is further improved when samples are made with Ru-3 leading to an increase of at least 420% over uniform Ru-1 samples. In addition to patterned materials, we explored the ability to frontally polymerize thin films on thermally insulating substrates. Using a combination of experiments and numerical simulations, the geometric limitations of FP are showcased, and the thin films are successfully manufactured down to a thickness of one millimeter. The results are used to build a scaling law which can be extended to other FP-based systems allowing the prediction of the thickness limit based solely on resin parameters measured using differential scanning calorimetry.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127350

Copyright and License Information

Copyright 2024 Luis E. Rodríguez Koett

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