EFFECT OF DYE STRUCTURE ON AFFINITY FOR FIBERS 127 



You will note the gradual increase in affinity as molecular size increases rela- 

 tive to the charge. Polar donor and acceptor type groups capable of associating 

 with the amide groups in the wool and more hydrophobic groups capable of 

 dissolving in the non-polar portions of the polymer chain are also effective in 

 helping fixation of dye. The ultimate use of this approach is the last example 

 where the molecule is constructed to emphasize the organic portion. This is a 

 prototype of a class of negatively charged metal complexes containing a few 

 simple hydrophilic groups. As a class these colors do not need protonated amino 

 groups to dye either wool or nylon. They are affinitive under neutral conditions, 

 and probably dye either as ions on amino groups or by dissolving in the fiber, 

 depending upon the application conditions and the particular structures. Evi- 

 dence of this is the ability of these dyes to reach a concentration level in nylon 

 beyond that which could be held on the terminal amino groups present. 



In conclusion, the last two illustrations (Fig. 17 and 18) present a summation 

 of the physical processes which appear to be involved in dyeing the various 

 fibers discussed. The picture ranges from a simple story for polyethylene tere- 

 phthalate to very complex situation for wool and particularly nylon which can 

 be dyed by a variety of mechanisms. 



Professor Pitzer: If you have evidence that this is really a solubility in the 

 body of the dyes, that is, in the volume of the material rather than on the sur- 

 face, then this is an extremely plausible picture in which there is merely a par- 

 tition equilibrium between the volume of the two phases. This is the sort of 

 thing happening on surfaces where you saturate a single layer and, there- 

 fore, run out of the type of site needed. It is not likely to happen because the 

 molar concentration in the interior of the materials is very low and there is no 

 particular reason to believe that the line would be other than linear. 



The other question, of course, concerns the interference when you were put- 

 ting on more than one dye and it seems to me this is subject, again, to pretty 

 simple physical-chemical interpretations if, again, they are going into the vol- 

 ume of the material. If each dye molecule is remote from any other, then they 

 are going to go in quite independently. On the other hand, if the two dyes do 

 in some manner get together in the material and have some direct interaction, 

 then there may be interferences which may be either positive or negative. In 

 other words, one may tend to draw the other one in or it may tend to force it 

 out. It depends upon the type of sites. 



