Quantifying Polymer Deposition
Figure 9: Fluorescence intensity profile across a hair fiber for which the 0.1% polymer solution was allowed to diffuse into the fiber cortex over 90 min. Fluo- rescence image of the fiber cross section shows that the width of the cuticle is about 4 μm.
pathways [12,13]. It is known that fluorophores generally require more than one hour to diffuse beyond the cuticle layer into the cortex of the hair fibers, so it was not expected that in the present experiments the polymer would penetrate into the cortex [14]. Te relative penetration of polymer into the hair fibers was determined by performing microfluorometry on cross sections obtained from the fibers that were previously analyzed in the study of polymer deposition on the cuticle. Te results from microfluorometry of the cross sections
suggest that at least some of the polymer penetrated into cuticle at all three concentration levels. Te fluorescence images gave the appearance of fluorescent rings (Figure 8). Te FI of the hair fibers were consistent with the results obtained from deposition of the polymer on the surface of the cuticle (Figure 7); the high- est polymer concentration (0.1%) had the highest FI, followed by the 0.01% solution, while the 0.001% polymer solution sam- ple had the lowest FI. Te epi-fluorescent cross-section images and distance scans shown in the inserts of Figure 8 indicated that the polymer diffusion into the hair fiber was limited to the cuticle or the surface of the cuticle. Te FI of the control specimen is shown in Figure 8D,
where the FI signal was barely above the background level. Te two peaks that appeared at a distance of approximately 30 mm and 110 mm, respectively, were artifacts. When the beam hits the edge of the hair fiber, a slight jump in FI is usually observed above the background level due to the com- positional differences between epoxy and the hair fiber. Te nearly black region inside the fluorescent ring was back- ground level and had a gray level similar to areas outside the cross-section. A long-term (1.5 h) diffusion experiment showed that
Figure 8: Fluorescence intensity profiles and cross-sectional FI images for hair fibers treated with: (A) 0.1% polymer solution, (B) 0.01% solution, (C) 0.001% solution, and (D) control (no added polymer). The oblique blue line on insert shows the path of the scan.
and through the inter-macrofibrillar cement. However, studies conducted on the diffusion of molecules into hair fibers suggest that we should consider all the structures within a hair fiber as diffusion pathways even though they may not form continuous
2019 July •
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the polymer can reach the center of the hair fiber (Figure 9). Tis experiment also revealed the width of cuticle in the flu- orescence image of the fiber cross section. Te cuticle width appeared to be about 4 μm, as expected.
Discussion Te cuticle is known to consist of 6–8 layers, each layer
being approximately 0.5 microns, giving a total thickness of approximately 3–4 microns [1]. Te application of the fluores- cent polymer for only 3 min (Figure 7) did not allow enough
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