Controlling viscosity to engineer focal conic domains in photonic cellulose nanocrystal films
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arXiv
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866911257852903424 |
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| author | Saraiva, Diogo V. Polling, Lotte Vermaire, Ivo R. Vonk, Sander J. W. Rabouw, Freddy T. Tran, Lisa |
| author_facet | Saraiva, Diogo V. Polling, Lotte Vermaire, Ivo R. Vonk, Sander J. W. Rabouw, Freddy T. Tran, Lisa |
| contents | Cellulose nanocrystals (CNCs) form cholesteric architectures that can have color specific reflectivity and enable sustainable photonic films. However, achieving uniform color, suppressing iridescence, and accessing ordered defect structures such as focal conic domains remain challenging. Here, we control the photonic properties of CNC films by steering the self assembly process. Across 24 dish-cast films with varying salt concentrations and sonication doses, we combine viscosity measurements, timelapse polarized optical microscopy, and angle-resolved reflectance spectroscopy to correlate evaporation dynamics with photonic structure. We show that viscosity, jointly controlled by NaCl-mediated electrostatic screening and sonication-induced bundle fragmentation, dictates the extent of tactoid coalescence. Low-viscosity suspensions generate large, homogeneous cholesteric domains and narrow spectral responses, while high viscosity leads to arrested, heterogenous domains and increased diffuse light reflection. Critically, within a narrow parameter window of intermediate ionic strength and moderate sonication, we reproducibly engineer photonically active focal conic domains. These results identify viscosity-driven flow as a key, previously underappreciated factor in CNC self-assembly and establish design rules for producing structurally colored films with tunable photonic response, reduced iridescence, and controllable defect architectures. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_06981 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Controlling viscosity to engineer focal conic domains in photonic cellulose nanocrystal films Saraiva, Diogo V. Polling, Lotte Vermaire, Ivo R. Vonk, Sander J. W. Rabouw, Freddy T. Tran, Lisa Soft Condensed Matter Cellulose nanocrystals (CNCs) form cholesteric architectures that can have color specific reflectivity and enable sustainable photonic films. However, achieving uniform color, suppressing iridescence, and accessing ordered defect structures such as focal conic domains remain challenging. Here, we control the photonic properties of CNC films by steering the self assembly process. Across 24 dish-cast films with varying salt concentrations and sonication doses, we combine viscosity measurements, timelapse polarized optical microscopy, and angle-resolved reflectance spectroscopy to correlate evaporation dynamics with photonic structure. We show that viscosity, jointly controlled by NaCl-mediated electrostatic screening and sonication-induced bundle fragmentation, dictates the extent of tactoid coalescence. Low-viscosity suspensions generate large, homogeneous cholesteric domains and narrow spectral responses, while high viscosity leads to arrested, heterogenous domains and increased diffuse light reflection. Critically, within a narrow parameter window of intermediate ionic strength and moderate sonication, we reproducibly engineer photonically active focal conic domains. These results identify viscosity-driven flow as a key, previously underappreciated factor in CNC self-assembly and establish design rules for producing structurally colored films with tunable photonic response, reduced iridescence, and controllable defect architectures. |
| title | Controlling viscosity to engineer focal conic domains in photonic cellulose nanocrystal films |
| topic | Soft Condensed Matter |
| url | https://arxiv.org/abs/2511.06981 |