Self-Assembled Monolayer Formation & Wettability

Deposition

Solution concentration med

Temperature 300 K

Tail Endgroup

Test Surface

Coverage

–

Packing order ψ₆

–

Molecules mobile

–

Contact angle θ

–

How it works

Thiol (–SH) or silane head groups dissolved in solution physisorb onto the substrate and diffuse across it as mobile precursors. When a headgroup lands on an empty docking site it chemisorbs — forming a strong covalent S–Au (or Si–O) bond — and locks in place. Neighbouring tails then pack together via van der Waals attraction, nucleating and growing ordered hexagonal domains until the surface saturates.

dθ_cov/dt ≈ k_ads·C·(1-θ_cov) − k_des·θ_cov
ψ₆ = |⟨e^(i6φⱼₖ)⟩| over locked neighbour bonds

Concentration — sets how fast new precursor molecules arrive from solution (Langmuir-like adsorption kinetics).
Temperature — faster surface diffusion helps precursors find empty sites, but also raises the desorption rate of loosely bound molecules.
Endgroup — the exposed tail chemistry (not the anchoring headgroup) sets the finished surface's energy: –OH/–COOH tails are polar and wet readily, –CH₃/–F tails are non-polar and bead water up.
Contact angle — Young's equation links surface energy to the angle a water droplet makes with the finished monolayer; a denser, more complete SAM pushes the angle further toward its endgroup's limit.

Endgroup: Hydrophilic (–OH)

Coverage vs. time

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