1. Hair Hydration Measurements Using Opto-thermal Radiometry and AquaFlux a Faculty of ESBE, London South Bank University, 103 Borough Road, London SE1 0AA, UK b Biox Systems Ltd, 103 Borough Road, London SE1 0AA, UK Perry Xiao ab and RE Imhof b

2. Opto-Thermal Transient Emission Radiometry (OTTER) Pulsed Laser Excitation Infrared Emission Signal Sample t t 9.5µm 13.1µm Heat Air Thermal diffusivity, D (m 2 s -1 ) Absorption coefficient to excitation light,  (m -1 ) Absorption coefficient to emission light,  (m -1 ) Layer structure

3. Opto-Thermal Skin Measurements

4. Opto-Thermal Delayed Thermal Wave (DTW) Measurements Opto-thermal delay time  t=L 2 /(  D) L : Epidermis thickness D: Epidermis thermal diffusivity Skin StratumCorneum Epidermis Dermis Heat absorbed by melanin & Haemoglobin L OPO Laser 420 ~ 590nm Thermal Delayed SignalAir

5. Opto-Thermal Skin Measurements Infrared Emission Signal Er:YAG 2.94µm StratumCorneum Epidermis Dermis Heat absorbed by water Air Skin

6. Opto-Thermal Skin Measurements Stratum Corneum Epidermis HydrationHydration Epidermis air H0H0H0H0 H0H0H0H0 H1H1H1H1 L Uniform Model Gradient Model

7. Opto-Thermal Skin Measurements

8. Opto-Thermal Measurements

9. Traditional Least-Squares Fitting Segmented Least-Squares Fitting

10. Opto-Thermal Measurements Time Depth 0 Transform Function

11. Opto-Thermal Hair Measurements

16. Condenser TEWL Method - AquaFlux

17. Condenser based, Closed- Chamber TEWL Measurements Technology Condenser -7.65 °C RH and Temperature Sensors Sample Ice

18. TEWL – Trans - Epidermal Water Loss TOWL – Trans - Onychial Water Loss TEWL and TOWL Measurements Stratum Corneum Epidermis Hydration air H0H0H0H0 H1H1H1H1 L W Jv J TEWL

19. Hair Desorption

23. Conclusions The results show that OTTER can be used to measure the water concentration and water diffusion within hair samples. OTTER signals can reflect the layered structure of hair, the water concentration depth profiles show that within hair water might not distributed uniformly. Hair samples appeared to be able to absorb a lot of water during 10 minutes soaking, and to hold on most of it during the next 20 minutes period. AquaFlux can be used for measuring the water holding capability of ex-vivo hair samples through natural desorption process. The results show that different hairs have quite different desorption processes which are likely indicating different water holding capabilities. By fitting the desorption curves with suitable mathematical models we can also extract the water diffusion coefficients of hair.

24. Acknowledgements We thank London South Bank University and EPSRC for the financial support.