Nanocellulose Structural Color 2D — Bouligand Stack Cross-Section

Cellulose nanocrystals suspended in water don't dry into a random tangle — driven by their surface charge, they self-assemble into a chiral nematic (cholesteric) liquid crystal in which each thin layer of rods is twisted a little relative to the one beneath it, building a helical "Bouligand" stack. This 2D companion renders that helix as the classic arched cross-section seen under a polarising microscope and applies the real Bragg selective-reflection law λ = n̄·P·cos(θ) to show, live, what colour the film reflects — with no pigment whatsoever. Tune the ionic strength used during drying to tighten or loosen the helical pitch, adjust the film's average refractive index, and tilt the viewing angle to watch the reflected wavelength blue-shift, exactly as it does in real iridescent nanocellulose coatings. Drag to pan across the stack and scroll to zoom into individual layers.