Many organisms in nature use structural color by way of periodic nanostructures to reflect different wavelengths of light for camouflage or signaling. These periodic nanostructures can be mimicked synthetically through the self-assembly of block copolymers (BCPs). The challenge of linear BCP self-assembly to visible light reflecting photonic crystals is that chain entanglement impedes the self-assembly of linear BCPs into nanostructures of required domain sizes. By tuning the macromolecular architecture of the BCP to reduce its capacity for chain entanglement more efficient self-assembly to large nanostructures is facilitated. Thus, with reduced entanglement it is possible to vary the molecular weight of the BCP to provide polymeric visible-light reflecting PCs that reflect wavelengths across the visible spectrum.<br/>Recently, it has been shown that dendritic BCPs can self-assemble to photonic crystals that reflect wavelengths of light across the visible light spectrum and into the near infrared depending on the molecular weight of the polymer. However, the current manufacturing capability of artificial photonic crystals on scale is a major obstacle to broadly implement this technology. Colloidal crystal arrays, lithography, or layer-by-layer deposition all require specialized equipment. Co-extrusion represents an economical process but geometries are limited and require specialized equipment to create photonic crystals. To address these concerns, we have synthesized dendritic BCPs that can self-assemble into visible light reflecting photonic crystals during the process of additive manufacturing. This BCP contains a dendritic polymer architecture that promotes a rod-like conformation, and in turn, a reduced capability for chain entanglement compared to the degree of entanglement within linear BCPs. Further, these dendritic BCPs possess high free energy parameters, as well as glass transition temperatures below melt extrusion 3D printing operating conditions which further enable them to self-assemble into photonic crystals that reflect wavelengths across the visible light spectrum during the process of 3D printing.

3D printing structural color with block copolymer based photonic crystals

2019 Spring National Meeting

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