This is the 2D-native counterpart to the 3D instanced-grime tile simulator. Instead of orbiting icosahedra scattered on a rendered slab, it draws the three things that actually generate the physics: a top-down grime concentration field on a cell grid (the reaction itself), the wetting cross-section that the contact angle literally is (a circular segment, not a revolved 3D surface), and a live semi-log kinetics plot that turns the exponential decay into a straight line whose slope is the rate constant.
1) Photocatalytic oxidation
TiO2 + hv(<387nm) -> e⁻ + h⁺
h⁺ + H2O/OH⁻ -> •OH (hydroxyl radical)
•OH + organic film -> CO2 + H2O
2) Photoinduced superhydrophilicity
UV photons eject lattice O, creating
surface Ti³⁺ / oxygen-vacancy sites that
dissociatively adsorb water -> surface
energy rises -> contact angle θ -> ~0°
Degradation follows pseudo first-order Langmuir–Hinshelwood kinetics for a dilute film:
-dC/dt = k_obs · C, k_obs ∝ I_UV
C(t) = C0 · e^(−k_obs t)
-ln(C/C0) = k_obs · t (straight line on the plot)
- Grid panel — every loaded cell's own concentration decays with the same k_obs = k_ref·I_UV; the aggregate grime coverage stat is the grid average.
- Cross-section panel — the same spherical-cap geometry as the 3D droplet (cap height h = R(1−cosθ), base half-width a = R sinθ) drawn as an actual 2D slice through the drop, so θ→0° flattens it and θ→180° rounds it into a near-sphere sitting on a point.
- Kinetics panel — plots −ln(coverage) against UV exposure time; while the lamp is on and no rinse is running this is a straight line whose slope is exactly k_obs, the direct experimental signature of pseudo first-order photocatalysis.
- Water Rinse — a front sweeps across the grid, stripping loosened grime at a rate that scales with how hydrophilic the surface currently is (low θ → water sheets and carries debris away; high θ → it beads and rinsing does much less).
Real self-cleaning glass and tile coatings rely on exactly this pair of coupled UV-driven effects — oxidative mineralisation of the grime film and a wetting-angle collapse that makes rinse water carry the byproducts off instead of leaving streaks.