Highlights

ESEM Studies of Fibers under Conditions of Varying Humidity

Scientific Achievement

Under the above mentioned proposal, two sets of experiments were performed: 1) determination of the affect of humidity on hair fiber properties and 2) investigation of tensile properties of hair using a custom-made tensile tester.  Understanding hair swelling is important because it is one of the criteria used to determine fiber integrity.  Using the Quanta FEG 400, we were able to observe differences in swelling behavior as a function of chemical treatment, including the swelling rates, Figures 1-3.  These experiments allowed us to determine that the ESEM is a viable tool to investigate the swelling properties of hair, and thus obtain information about hair fiber integrity.  Future investigations to understand the contributing factors of swelling and its role in fiber integrity will include studying fiber modifications of the morphology and distribution of cuticles during and after humidity cycles.

Secondly, we attempted to mimic ‘real-life’ fiber stresses in the ESEM chamber to determine modes and propagation of fracture using a custom designed tensile stage.  This preliminary investigation yielded information regarding the mechanism of fiber breakage, which is the number one hair concern of African-American women.  From these experiments, we were able to correlate a stress/strain curve with morphology and geometric alterations of hair fibers, Figure 4.  For example, it was possible to track the initiation of cuticle fraying and the subsequent formation and propagation of cracks.  After the fiber broke, the type of hair facture was determined to be a step pattern, Figure 5.  Future experiments will include investigating the mode of fracture at varying relative humidities.

In conclusion, these two sets of experiments allowed us to determine the applicability of the ESEM to study the dynamic behaviors of hair under varying conditions.

Significance

The ability to use the ESEM to study hair fibers, while mimicking various environmental and grooming conditions, has not been demonstrated previously.  The majority of previous work was performed in high vacuum with metallically coated fibers or at low voltage to mitigate the affects of charging.  These techniques provided spectacular images of the cuticle, but they do not always relate to the state of the fiber under ambient conditions, specifically due to the dehydration of fibers under high vacuum.  Because of this, the results obtained from these experiments need to be interpreted with care.  However, the ESEM allows for the direct observation of fiber properties, not only under ambient conditions, but also under varying humidity and load.  This work was presented at the Microscopy and Microanalysis conference in 2006 and 2007.  See proposal for references.

Performers

S. Diridollou, P. Hallegot (L’Oreal); N. J. Zaluzec (Argonne-MSD)