Polymer Chain-Population Photooxidative Scission

UV Exposure Conditions

UV intensity (sun exposure) 70%

Ambient temperature 32°C

Dissolved O₂ availability 80%

Population State

Chains (fragments)

Chain scissions

Relative Mₙ

100%

Exposure time

0 d

How it works

The 3D companion sim follows one particle's surface as a bonded lattice network. This 2D sim instead follows a whole population of polymer chains at once, and plots the one quantity that random photooxidative scission actually predicts: the population's number-average degree of polymerization, Mₙ.

Photooxidation breaks backbone bonds essentially independently of one another — each live bond has the same per-bond scission rate k, set by the same Arrhenius law as the 3D sim:

k = Φ · I_UV · exp(−Ea / RT) · f(O₂)

Φ    = quantum yield of chain scission per absorbed photon
I_UV = UV irradiance (intensity slider)
Ea   = 42 kJ/mol, activation energy of the radical propagation step
R,T  = gas constant, absolute temperature (temperature slider)
f(O₂)= 0 in anoxic conditions, rising to 1 as O₂ availability increases

Every bond break adds exactly one new chain to the population, so after b(t) total breaks the number-average chain length falls from Mₙ(0) to M/(N₀+b(t)) where M is the (conserved) total monomer count and N₀ the starting chain count. Because each of the B₀ = M − N₀ original bonds breaks independently at rate k, its survival is a simple exponential — giving the exact, closed-form Saito random-scission law plotted live below the sliders:

1/Mₙ(t) − 1/Mₙ(0) = (B₀/M)·(1 − e^(−kt))
                   ≈ k·t     for long chains, small kt

UV intensity, temperature, O₂ — set the same per-bond rate constant k as the 3D sim; higher values make every bond in every chain break faster.
Unlike the 3D lattice, no bond here is more "exposed" than another — random main-chain scission is (to first order) a bulk, not a surface, process, which is exactly what the linear-in-time Mₙ decay shows.
Each break splits one chain into two independent chains that drift apart — the fragment count rising 1:1 with the scission count is the direct visual signature of the b(t) = N(t) − N₀ relation used above.

UV photon strike Original chain Scission fragment