Soft Materials Seminar - "Design, Fabrication and Mechanical Testing of Photo-Patterned Semi-Crystalline Materials"

In this study, we fabricated poly(1,5-cyclooctadiene) [p(COD)] using Ring-Opening Metathesis Polymerization (ROMP) with a thermally activated catalyst and used light to control the crystallinity. However, after polymerization, residual active initiator and chain ends undergo secondary metathesis. This can cause cis-to-trans double bond conversion causing the crystallinity to evolve over time affecting the mechanical properties. To address this, we investigated a method for deactivating the catalyst and preventing the progression of increasing crystallinity over time. By using a photo-based generator that when activated releases a base that prevents further metathesis. By varying light intensity and exposure time we can create distinct regions with varying crystallinity, which allows us to create any predefined pattern on the structures. Specimens were fabricated incorporating patterns such as lizard scales, circular hexagonal packing array, and vertically aligned lamellae. Non-patterned samples were used as a benchmark and were irradiated at 0 hours, 24 hours or 72 hours. Samples were subjected to uniaxial tension, and we used digital image correlation (DIC) to capture the fully localized strain field. We observed non-homogenous variation in the localized strain for the patterned materials, whereas non-patterned samples displayed a homogenous localized strain. Through controlling light intensity and pattern type during fabrication, we can induce mechanical gradient properties in materials and locally tune the strain distribution of polymeric materials. Using light to develop complex high-resolution patterns enables exact predesign of polymeric materials. In this present work, we investigated a novel fabrication technique for patterned structures and DIC supported mechanical characterization allowed us to have a deeper understanding of the mechanical behaviors of the patterned samples at multi-scale length.