DWR Re-Proofer Coating Uniformity Simulator

Physics-based computational model  ·  qualitative predictions only  ·  A. Stubbings (MEng Materials Science)  ·  github.com/arthurstubbings/dwr-sim
Polymer loading φ₀ —
Yarn crimp —
Drying rate vevap —
Polymer particle radius rL —
Effective DWR Coverage
0 1
Bright = high coverage (valleys pool more polymer)  ·  grey = pore
Contact Angle Map (Cassie–Baxter)
— —
Blue < 90° (wets)  ·  red > 90° (beads)  ·  grey = open pore
Beading Index
—
Crown-weighted [0–1]  ·  relative metric
Contact Angles
Crown  (droplet rests here) —
Valley  (interstice) —
Mean —
⚠  Crown starvation
Crown CA < 90° — crowns wet
Polymer pools in valleys,
starving surfaces a drop rests on
↕  Uneven coating
Crown CA < Valley CA
Both bead, but polymer skewed
toward interstices
✓  Crowns adequately coated
Crown CA ≥ Valley CA — uniform
Process Window  (beading index)
→  Drying rate (slow → fast)    × = current params
↑  Polymer loading (dilute → concentrated)

Key Finding — Pooling Starves the Crowns

Capillary pressure pulls the re-proofer dispersion into the inter-yarn interstices, leaving a locally thicker residual film there than on the exposed yarn crowns. Thicker films have a higher local film Péclet number: the evaporative flux buries the functional polymer in the deposit rather than leaving it at the air surface where it lowers the contact angle a raindrop feels.

The result: repellent pools where it is not needed and starves the yarn crowns — the very surfaces a raindrop actually rests on. Crown CA < 90° means the fabric wets despite carrying DWR.

The process window (adequate loading + slow/cool drying) keeps local Péclet numbers low enough for diffusion to re-homogenise the deposit before the film collapses.