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Hair Mechanical Anisotropy-What Does It Tell Us?
Steven Breakspear1, Bernd Noecker1, Crisan Popescu1
1Kao European Research Laboratories, KAO Germany GmbH, Darmstadt D-64297, Germany (S.B., B.N., C.P.).
Journal of Cosmetic Science
|February 16, 2019
Summary
This study reveals how hair fiber
Area of Science:
- Materials Science
- Biophysics
- Textile Science
Background:
- Hair fibers exhibit complex mechanical properties influenced by environmental factors.
- Understanding hair's anisotropic behavior is crucial for material science and cosmetic applications.
Purpose of the Study:
- To investigate the mechanical anisotropy of hair fibers.
- To determine the relationship between anisotropy and moisture content.
- To correlate mechanical anisotropy with hair fiber's internal structure.
Main Methods:
- Atomic force microscopy and nanoindentation were employed to measure mechanical properties.
- Young's modulus was evaluated along (longitudinal) and across (transversal) the hair fiber.
- Anisotropy index (IA) was calculated as the ratio of longitudinal to transversal Young's modulus at varying relative humidity levels.
Main Results:
- The anisotropy index (IA) of hair fibers varies with relative humidity.
- A composite material model was used to link IA to the fiber's internal architecture.
- Results suggest a specific micro-structure of the exocuticle, typically masked by cross-linking, becomes apparent upon moisture absorption.
Conclusions:
- Hair fiber's mechanical anisotropy is humidity-dependent.
- The study provides insights into the hair fiber's micro-structure, particularly the exocuticle.
- Moisture absorption plays a key role in revealing the mechanical properties of the exocuticle.
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