Materials Science

Hierarchical organization of structurally colored cholesteric phases of cellulose via 3-d printing



Structural color—a widespread phenomenon observed throughout nature is caused by light interference from ordered phases of matter. While state-of-the-art nanofabrication techniques can produce structural organization in small areas, we still lack a cost-effective, and scalable techniques to generate tunable color at sub-micron length scales. In this work, we produced structurally colored hydroxypropyl cellulose filaments with a suppressed angular color response by 3-d printing. Our systematic study of the morphology of the filaments reveals the key stages in the induction of a two-degree hierarchical order through 3-d printing. The first degree of order originates from the changing of the cholesteric pitch at a few hundred nm scale via chemical modification and tuning of the solid content of the lyotropic phase. Upon 3-d printing, the secondary hierarchical order of periodic wrinkling was introduced through the Helfrich-Hurault deformation of the shear-aligned cholesteric phases. Our work reveals the mechanism of the wrinkling behavior evidenced by detailed morphological characterization using SEM. In single layered filaments, we identified four morphological zones with varying order of wrinkles. Through this work, we demonstrate the possibility of modifying the wrinkling behavior and thus the angle dependence of the color response by changing the printing conditions.


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Supplementary material

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Hierarchical organization of structurally colored cholesteric phases of cellulose via 3-d printing-Supplementary work
SI file includes Figure S1: photographs of wet printed HPC samples; Figure S2: angular photography of dry printed HPC samples Figure S3: cross-linking reaction steps of HPC with GA; Figure S4: FTIR data Figure S5/ S6: NMR data Figure S7: photographs of pristine and cross-linked HPC Figure S8: TGA data Figure S9 printed samples of HPC used to demonstrate effect of drying at a different temperature Figure S10: photograph of a doctor-bladed HPC sample which varies in thickness Tables S1 and S2: thickness and spectral data corresponding to points defined on Figure S10 Figure S11: plotted data from Table S1 and Table S2; Figure S12: 64 wt % HPC GA samples printed at different pressures using the different nozzles Figure S13: SEM micrographs of printed single filament sample cross-sections Table S3: Measurements of wrinkles in zones B and D; Figure S14: Illustration of settings used for 3-d printing of constructs