Hair care is an important part of Unilever's Home and Personal Care business. The physical appearance of hair is closely correlated to its microstructure, and although the microstructure of hair is well known [1], the fine detail of its control has eluded us because of the considerable natural variation within the hair itself. We have developed a method using the ID02 high-brilliance beamline to combat this natural variation and furthermore permit quantification of the change in microstructure as a consequence of some physical or chemical perturbation, essentially using the hair as its own control. Figure 147a shows the small-angle scattering from a single hair fibre. Each image represents the scattering from the hair at nine points along the fibre separated by 0.5 mm. The radial average of this data is shown in Figure 147b and this demonstrates the reproducibility obtainable within a single fibre itself.

Fig. 147: (a) SAXS images from nine points along a single fibre separated by 0.5 mm, (b) the radial averaged data plotted as an overlay.


Although the "intra-fibre" reproducibility within this 4 mm length is excellent we find that if we venture outside these boundaries data consistency is lost. Furthermore comparison of the scattering from adjacent hairs with the average from the first hair, (Figure 148), shows that the "inter-fibre" reproducibility is less good.

Fig. 148: Comparison of inter fibre scattering between different hairs. The black is the average scattering from Figure147, these are compared to the beginning (pink), middle (green) and ends (red) for two other fibres taken from the same woman's head.


Ergo quantification can only be performed on a single fibre and considered as the displacement from a fixed starting position. This approach has been used to determine the effect of varying humidity for both virgin and bleached human hair in response to changes in humidity, and the humidity-dependent variation in micro-fibril separation is shown in Figure 149.

Fig. 149: Change in microfibril separation with humidity (RH).


Each data point is the average of five measurements along an individual fibre and the error bar represents the standard deviation on the value reported. The red curve highlights the problem faced in terms of acute substrate variation, and more data is currently undergoing analysis. Despite each hair starting from a different absolute value, a consistent change in peak position is observed with increasing relative humidity, and an interesting trend is observed where the response to change in humidity appears to change between 50 and 60% relative humidity. Work in progress [2] will provide evidence to show that this behaviour is consistent with the two-phase mechanical model of Feughelman [3]. The marriage of controlled humidity equipment with the beamline was not straightforward and the contributions of the ID02 team are gratefully acknowledged.

[1] Chemical & Physical Behaviour of Human Hair, C. Robbins, 2nd Ed., New York, Van Nostrand, Reinhold Co. (1988).
[2] I.M. Tucker, F.I. Bell, Y. Leray, P. Carpenter, T.E. Lyons, J. Hubbard, S. Ward, P.A. Cornwell, N. Theyencheri, P. Panine, T. Weiss, T. Oikawa, R. Skinner, submitted to Biochimica et Biophysica Acta-General Subjects, (Dec 2003).
[3] M. Feughelman, Textile Res. J., 29, 223-228 (1959).

I.M. Tucker, R. Skinner, T.E. Lyons, J. Cotterall.
Unilever Research & Development Port Sunlight, Wirral (UK)