The reactions of monolayers of model proteins (edestin and a wool derivative) on acid solutions of a number of 1:1-chromium-ligand dyes, of both monosulphonated and disulphonated types, and certain nonmetallized sulphonated dyes of similar structure, have been studied. Measurements of film area, pressure, compressibility, and viscosity have been made. All sulphonate groups appear to enter the water. Thus monosulphonated dye molecules penetrate between the protein chains, reducing the film viscosity, whereas disulphonates orient horizontally beneath the protein. A free —OH group present in the dye molecule causes it to bind more firmly to the protein, with increase in film viscosity and in surface compressional modulus (scm). All the dyes appear to act just as do the nonmetallized counterparts: film areas are increased; monosulphonates form mixed films and reduce both viscosity and scm of the film; disulphonates produce no change in viscosity or slope of the π/A curve but slightly increase the scm; the pressure-area changes are reversible. The viscosity of the protein film over a simple chromium salt solution alone, however, is very greatly increased. Evidence is obtained that reactions of the present protein films with dyes can reasonably be used to interpret dye-wool bonding reactions. There is no evidence from the present tests that the chromium atom in the dye molecule forms any bond with the protein. The good wash fastness which these dyes in wool have in technical practice must, therefore, be due solely to their high molecular weight and to mechanical effects of the structure of the fiber.

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Surface-tension measurements of three wool-reactive dyes in water-benzyl alcohol mixture show that, contrary to previous hypotheses, the presence of the organic solvent depresses the concentration of dye at the interface with air, and most probably with wool. It is suggested that this effect accelerates dye diffusion into the fiber by reducing “drag” of diffusing dye molecules in the intermolecular channels of the fiber. Determination of surface pressure/area relationships and surface-film viscosity measurements at measured times after spreading protein monolayers on acid solutions of the same dyes in pure water and solutions of dimethyl formamide, methanol, isopropanol, n-butanol, and benzyl alcohol, respectively, shows that the presence of solvent accelerates covalent bond formation between dye and protein. It is suggested that the solvent shields hydrophobic regions of the protein and allows easier access of the dye to the reactive polar groups in the protein; also, it may retard the side reaction of dye with water. This accelerative action may not be important in dyeing with nonreactive dyes, because the ion-ion reaction between these and the fiber is probably much more rapid than the covalent bond formation of the reactive dyes. It is suggested that to accelerate dyeing, dyebath assistants should be surface-active but not likely to form mixed micelles with dye.

Monolayers of edestin, as a model for protein fibers, have been spread on water and on aqueous solutions of three wool-reactive dyes with and without the addition of urea. The film area, compressibility, and viscosity values were measured and interpreted. Surface tension measurements on aqueous solutions of the dyes agree qualitatively with the expected effects of their structural differences. The most surface-active dye, containing a single reactive group, penetrates the protein film rather slowly, slightly increasing the compressibility. On standing overnight, dye-protein reaction occurs, and the film becomes more rigid. A dye with two reactive groups causes a marked increase of rigidity of the film, and the dye-fiber reaction appears to be more rapid than the rate of dye penetration into the film. The third dye, with a single reactive group, is intermediate in effect on the film. Urea expands the film and appears to open the protein structure without causing crosslinking. In presence of dye the more open protein structure appears to persist but on standing the film rigidity increases.