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Colin D. Bain coauthored research on monolayer.^[ref]

A monolayer is a single layer of chemical atoms or molecules. In the Langmuir adsorption model, a complete monolayer occupies every adsorption site; partial surface coverage leaves vacancies within that first layer. One layer need not mean one molecule per surface chemical atom.

George M. Whitesides coauthored experiments controlling the surface order of thiol monolayers on gold. Hydroxyl-terminated chains and mixtures of chain lengths connect molecular organization with surface hydrophilicity.

The chemical identity of a terminal group is only part of the surface specification: packing and the surrounding chains can change how that group is exposed.^[ref]

Use a self-assembled monolayer of an alkanethiol with a polar terminal group, such as $\mathrm{HS}(\mathrm{C}{\mathrm{H}}_2{)}_{\mathrm{n}}\mathrm{OH}$. Sulfur anchors to gold while the exposed hydroxyl groups interact favorably with water. A methyl-terminated monolayer would instead present a low-polarity outer surface and usually retain hydrophobic character.

Prepare a clean gold surface, allow adsorption from a compatible clean solution, and rinse away unbound material. Dense coverage and molecular ordering help make the terminal chemistry reproducible. Mixed chain lengths or incomplete coverage can change the wetting response, so the presence of an OH group in the bottle alone is not sufficient. An original experiment demonstrated hydrophilic hydroxyl-terminated films and showed that mixing chain lengths changed surface order and wettability.^[ref]

This specifies the resulting interface rather than treating every freshly prepared gold surface as intrinsically identical: contamination, preparation and adsorbates influence the starting contact angle.