CONDITIONERS AND HAIR FIBER HARDNESS 583 erably larger number of the same single hair fibers (root sections) before and after multiple applications of the conditioner, to be able to statistically verify the results of the earlier feasibility study. An attempt was made to rinse the fibers thoroughly to remove conditioner deposits from the surface. Observations in the microscope confirmed that a "clean" cuticle surface was obtained and indents were made in close quarters on adjacent scale faces of the same hair fibers before and aj9er application of the cationic condi- tioning compound. The results were analyzed by appropriate procedures to highlight the effects of the conditioner on fiber mechanical property. HEIGHT/AMPLITUDE IMAGES AND 3-D HEIGHT IMAGES BEFORE/AFTER NANO-INDENTATION Figures 2a and 2b are typical examples of height and amplitude images of the real-time nano-indentations made on the scale faces of the same untreated and conditioner-treated hair fibers (obtained in the tapping mode), respectively. As can be seen in these figures, the indents were carefully placed on relatively "flat" areas to eliminate problems with the curvature of the hair fiber. A magnified version of indents shown in the height and amplitude images in Figures 2a and 2b is displayed in "real time" 3-D height images in Figure 3. The images of these indents were recorded in "real time" for subsequent profile scanning analysis to measure the indentation depth. "Real time" acquisition of the images of the indents is important to avoid errors in depth measurements due to partial recovery of the material. Differences in indentation depth between the untreated and conditioner-treated cuticle surface can be attributed to the effect of the conditioner on the hardness of the "scale face." PROFILE SCANNING ANALYSIS OF THE REAL-TIME IMAGES OF THE INDENTATIONS It is very difficult to make quantitative statements about changes in the microhardness of the scale faces of the fiber based on the 3-D images alone. Therefore, "profile scanning analysis" is used to interpret the data by measuring the vertical depth of the saved "real time" images of the indentations. Recording the indents in "real-time" is an important aspect, since it stores an image of the actual indent prior to recovery of the deformed substrate. Typical examples of the profile scans across three sequential indents are shown in Figures 4a and 4b along with the corresponding "real-time" height images of the untreated and conditioner-treated hair fibers. Evaluation of the indentation data. Evaluation of the nano-indentation depths made on flat, "clean" regions of the scale surface (devoid of detectable conditioner deposits) clearly shows a definite decrease in microhardness after multiple conditioner treatments. We feel that this softening effect of the scale faces is strictly due to the hydrophilicity of the polymer present on the keratin surface. Its applicability to cosmetic effects was not the goal of this study. The change in surface hardness is indicated by the scatter plot in Figure 5, showing 42 paired sets of depths of nano-indentations made on the same hair fibers before and after conditioner treatments. The mean values and standard deviation of the indentation depths show statistically significant differences (at 95% confidence level) between 49.4 nm + 5.6 for the uncon- ditioned hair and 61.9 nm + 8.8 for the conditioned hair. The result of the t-test yields

584 JOURNAL OF COSMETIC SCIENCE ! 0 10.0 •M 0 I0.0 • Data t•pe Height Data t•pe AMplitude 2 range 1000.0 nM 2 range 0,5000 U i 0 10.0 pM 0 10.0 p• Data t•pe Height Data t•pe AMplitude 2 range 1000.0 nM 2 range 0.5000 U i 0 10,0 PM 0 10,0 Data •pe Height Data t•pe AMplitude 2 range 1000.0 nM 2 range 0.5000 U b 0 10.0 p• 0 10.0 p# Data t•pe Height Data t•pe AMplitude 2 range 1000,0 nM 2 range 0.5000 U Figure 2. a: Height and amplitude images before (top) and after (bottom) sequential nano-indents on the surface cuticles of the same untreated hair fiber. b: Height and amplitude images before (top) and after (bottom) sequential indents on the surface cuticles of the same conditioner-treated hair fiber.