334 JOURNAL OF COSMETIC SCIENCE CORRELATION OF AFM/LFM WITH COMBING FORCES OF HUMAN HAIR Roger L. McMullen*', Stephen P. Kelty' and Janusz Jachowicz* •Department of Chemistry, Seton Hall University, South Orange, N J, and *International Specialty Products, Wayne, N J, Introduction Scanning Probe Microscopy (SPM) is a class of techniques used to study the surface properties of materials from the atomic to micron scale. Atomic Force Microscopy (AFM) and Lateral Force Microscopy (LFM) fall under the SPM umbrella of techniques. h• both these techniques, a sharp tip stylus is placed in contact with a surface to be investigated. In AFM, one obtains a topographical image by measuring the deflection of a soft cantilever, to which the tip is attached, as the tip is tastered over the surface. The cantilever deflections normal to the surface are representative of topographical surface features. In LFM, one measures the torsional twisting of the cantilever as it is tastered over the surface. These lateral cantilever deflections result from drag forces between the tip and sample surface. Although several AFM investigations on human hair fibers have recently appeared in the literature, to our knowledge, complementary LFM studies have not been forthcoming. However, there has been a limited amount of information reported concerning tlxe LFM of wool fibers in which different frictional domains were observed [1]. Within the realm of human hair fiber invest/gations, a considerable amount of interest has focused on quantifying the cuticle step heights [2,3], and characterizing the surface roughness of the morphological components of the cuticle, i.e. the exocuticle, endocuticle, and the A-layer [3]. Additionally, these studies have demonstrated the use of AFM to study hair at various degrees of hydmtion [1-4] and at a range of pH levels [4,5]. Other studies, primarily interested in the adsorption of cationic polymers onto hair, have also been completed [6-9]. Most recently, Parbhu et. al. used force-volume and nano-indentation techniques to measure the hardness and relative elastic moduli of the morphological components of the wool fiber [10]. Their results were in agreement with what one would expect considering the chemical composition of the various components of the wool fiber. We herein report combined AFM and LFM investigations of hair fibers as an analytical tool to correlate the wet combing force (obtained using a Miniature Tensile Tester) for bulk fibers. A comparison is made using both the surface topography (AFM) and the frictional force (LFM) obtained for a single fiber with the bulk fiber assembly. Hair that has been weathered (irradiation), chemically treated (bleached, permanent waved, or dyed), or thermally exposed (curling iron or hair dryer) experiences an increase in wet combing forces. Spatially Resolved Combing Analysis allowed us to observe an increase in inter-fiber friction, in the area of the hair t•ess, where the damaging treatment was administered. Methods & Results AFM and LFM studies were performed using an AutoProbe TM CP manufactured by Park Scientific Instruments. An AFM/LFM probe head was used in conjunction with a 100 gm piezoelectric scanner, operating in the contact mode. Commercial gold-coated Si3N4 cantilevers with pyramidal tips (microlevers) were used in the analysis. Hair fibers were mounted to steel sample studs using epoxy or nail polish. All data sets were collected in the contact imaging mode. During each scan, images were obtained for the topographic, error signal, left-to-right LFM, and right-to-left LFM measurements simultaneously. Subsequent data analysis was performed using Image Tool 2.0 (University of Texas Health Science Center in San Antonio). All image data presented in this report is raw and otherwise unfiltered. In normal operation, the difference between actual cantilever deflection and a reference setpoint is supplied to a feedback loop connected to the z-drive (height) of the scanner. The voltage supplied to the z-drive is the origin of the topographic image data and is sensitive to topographic surface features. The error signal image reflects the difference between tlxe actual cantilever deflection and the setpoint and is highly sensitive to changes in height. Consequently, we find that it is useful to monitor both the topographic and error signal simultaneously since they are complementary techniques. LFM data were

2000 ANNUAL SCIENTIFIC SEMINAR 335 obtained in both scan directions providing ns with two complementary images illustrating the torsional bending experienced by the cantilever in the leR-to-right and right-to-leR scan directions. Combing measurements of hair tresses were performed using a Miniature Tensile Tester (Dia-Stron Ltd.) operated by M'YFVqI• 4. la soRware. Oriental human hair (International Hair Importers & Products, Inc.) was used for all investigations due to its high radius of cu.,'vature as compared to other hair types, which are more elliptical in shape. Virgin hair, as supplied by the distributor, was compared with hair that was extracted with a series of solvents. The effect of solvent extraction on hair was investigated first by extraction with t-butanol and n-hexane, each for 4 hours, then with a mixture of chloroform/methanol (70:30 v/v) for 6 hours. For each extraction procedure, 3 g of hair was extracted with 250 mL of solvent. Additionally, we examined the effect of bleaching hair by using a commercial bleaching system consisting of Clairol Professional BW 2 bleaching powder and Emiliani Professional 20 Volume clear developer. In an attempt to correlate data obtained from a miniature tensile tester with AFM/LFM data, we will present the combing analysis of untreated hair and hair that has undergone the treatment protocols described above. We will also discuss the image analysis of data obtained from AFM/LFM. For demonstration, topographic, error signal, LFM (left-to-right), and LFM (right-to-left) images have been included in Figures 1-4, respectively. These images were obtained simultaneously for a 20 •m 2 scan area on untreated hair. The scale in Figure 1 correlates darkly colored areas with lower topography and lightly colored areas with regions of higher topography. The error sign,-fi does not provide us with useful topographic information, however it does offer informative boundary data, which can be used to determine the size of features in the xy plane. The LFM data, included in Figures 3 and 4, demona'tmte the torsional bending of the cantilever as it rasters across the sample in both directions. It is important to note that what appears dark in Figure 3, transpires as light in Figure 4 and vice-versa. In Figure 3 (left-to-right) dark represents areas that are higher in friction whereas light is indicative of lower frictional regions. The opposite is true for Figure 4 (right-to-left), in which light corresponds to high friction and dark represents low friction. By talcing the difference between Figures 3 and 4, one can obtain relative frictional information about a particular material. However, the images must be collected at various normal forces in order to obtain a plot of torsional cantilever deflection as a function of the set point. In this study we compare virgin with solvent-ex-tracted and bleached hair. Figure 5 provides preliminary data for each of these hair types in which the difference in the left-to-right and right-to-left LFM signals are plotted as a function of the normal force applied by the probe. The slope for each hair type, which is related to the frictional coefficient between the probe and a given hair surface, is reported in the Figure and demonstrates a larger slope for bleached and solvent extracted hair thaa for virgin hair. For bleachd hair, such a result is in agreement with evaluation of mechanical combing forces which suggest higher dry combing works as compared to virgin hair. (1) Phillips, T. L. Horr, T. J. Huson, M. G. Turner, P.S. Text/'/e Res. J. 1995, 65, 445-453. (2) Smith, J. R. J. Microscopy 1998, 191, 223-228. (3) Smith, J. R. J. Soc. Cosmet. Chern. 1997, 48, 199-208. (4) O'Connor, S. D. Komisarek, K. L. Baldeschwieler, J. D. J. /nves& Oerrnato/. 1995, 105, 96-99. (5) You, H. Yu, L. Scanning 1997, 19, 431-437. (6) Goddard, E. D. Schmitt, R. L. Cosmet. & Toil 1994, •09, 55-61. (7) Schmitt, R. L. Goddard, E. D. Cosine& & Toil 1994, 109, 83-93. (8) H•ssel, P. Sander, R. Schrepp, W. Cosmet. & Toil. 1996, I I 1, 57-65. (9) Pfau, A. H6ssel, P. Vogt, S. Sander, R. Schrepp, W. Macrorno/. Syrnp. 1997, •26, 241-252. (1 O) Parbhu, A. N. Bryson, W. G. Lal, R. Biochemistry 1999, 38, 11755-11761.