Switchable water-based paint or coating compositions

A method of forming a film on a substrate, comprising:

• applying to a substrate a composition comprising:
• a liquid medium;
• and
• a polymer that has a Tg in the range of from about 20° C. to about 50° C., and that comprises protonatable moieties, wherein a portion of the protonatable moieties are in their protonated form such that the degree of polymer protonation is sufficient to at least partially solvate the polymer in the liquid medium;
• the liquid medium comprising water or an aqueous solution and an acid gas dissolved at a concentration sufficient to maintain said portion of protonatable moieties in their protonated form;
• crosslinking the composition, the composition comprising at least one cross-linking agent,
• wherein the at least one crosslinking agent is inhibited from cross-linking by the dissolved acid gas,
• wherein, when the composition is applied to the substrate under ambient conditions the concentration of dissolved acid gas decreases such that some or all of the portion of protonatable moieties switch from their protonated form to their non-protonated form and the degree of polymer protonation is reduced such that it becomes insufficient to maintain the at least partial dissolution of the polymer in the liquid medium, and the polymer forms a film that is substantially water-insoluble, water-resistant, and/or hydrophobic.