MECHANICAL PROPERTIES OF HAIR 81 SO F(fl [graf) INDEX OF RELAXATIOa5 ©• - , •, ....... •...• -- -tõ io- ............... 0 0 ' , , , , , , , , i]00 t0 20 ]0 40 50 BO 70 liO 90 ! I OF RELATIVE HUMIDITY znd whcz• oHgoszcchzfid½s zs follows: FI - 1, znd I• - 2 ooe un•rcz•½d fibers znd FI - 3, znd I• - emulsions, except for the glycerine and propylene glycol systems that gave rise to fibers with a strong hysteresis effect. In Figure 14 it is shown, for instance, that as moisture increases, hairs de-immersed from glycerine and propylene glycol follow the normal behavior shown by untreated fibers. However, once the fibers have been brought to a high humidity level, their F(1) and IR Values do not change appreciably as moisture is decreased, i.e., the F(1) and IR equilibrium values of the two half portions of the hysteresis cycle differ significantly. Further moisture cycles did not seem to cause any change (see Figure 14). The dependency of F(1) and length variations presented by most fibers immediately after immersion in the liquid systems suggests that moisture transport between hair and solution equilibrates through a water partition mechanism that is strongly dependent upon the water structure and water concentration in the liquid system. For instance, when hair is conditioned at 87% RH and immersed in the oils, glycerine, and propylene glycol, all conditioned at 10% RH (see Figures 1 and 13), and in the saturated solutions of LiCI, CaC12, and urea (see Figures 8 and 9), length contractions and F(1) increments take place because water is transferred from hair to the immersion system. Conversely, when hair conditioned at 5 % RH is immersed in saturated solutions of LiCl and CaC12, the oils (see Figure 1), glycerine, and propylene glycol (the latter three conditioned at 87% RH see Figure 13), or if hair conditioned at 87% RH is immersed in the emulsions and the saturated solutions of NaCI, MgC12, or citric acid (see Figures 8, 9, and 13), then the hair swells and F(1) decreases because moisture is transferred

82 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I OF F[1) VARTATTOI o to 21) 11 4o TIXE (MINUIES) Figure 13. Percentages of F(1) variation as a function of time of fibers immersed in the following systems: methanol, (1 m) ethanol, (1 /•) propanol, (1 O) glycerine, (2 *) propylene glycol, (2 O) w/o, 50/50 water/lanolin emulsion 3600 cSt, (3) o/w, 50/50% PEG lanolin emulsion 4200 cSt (4) and de-ionized water (5). from the immersion system into the hair fibers, although the degree of swelling and F(1) decay is not as high as in the case of de-ionized water. The effects of liquid systems that produce only unidirectional changes in F(1) and fiber length regardless of the moisture content in hair and solute concentration can, thus, be explained by their less organized water structure. According to these arguments, the availability of water for hair, upon immersion, will be higher in the aqueous solutions of proteins, Na2CO3, and NaNO3, while in the emulsions and saturated solutions of LiCI, CaC12, NaC1, and MgC12, hair will compete for water in a more structured environment. As has already been shown by some researchers, water forms part of a highly ordered structure in solutions of these salts and in some emulsions (43,44,48). The particular behavior of urea solutions in hair seems to indicate that immediately after immersion, moisture exclusion from hair takes place by a water-partitioning mechanism and, as a consequence, the fiber contracts. As time elapses, however, with the simul- taneous diffusion of urea into the amorphous matrix of hair, swelling by hydrogen bond breakage becomes the dominant process. The case of saturated solutions of LiCI might follow similar lines of reasoning, although, instead of swelling, one would expect super-contraction to occur (40,41). It seems thus, in general, that before oils, ions, or solvents diffuse into the hair shaft, the fiber undergoes a moisture equilibration process. In order to elucidate the role of moisture on the F(1)s, IRs, and length dimensions of fibers at different equilibrium conditions, several fibers were subjected to hysteresis