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Studies to understand the rates of moisture adsorption and desorption in hair

corresponding

TREFOR EVANS
TRI Princeton, New Jersey, USA

Abstract

Improved knowledge pertaining to the adsorption rates of moisture in hair has relevance in attempts to elucidate pathways for prolonging temporary heat-induced hair styles. Specifically, there is desire to understand whether such rates can be manipulated by external treatments. The Dynamic Vapor Sorption (DVS) technique is a suitable approach for performing such testing; but, at the same time, many experimental variables can influence results. As such, without recognition and control of these variables, there is potential for results and conclusions to be muddled by experimental artifacts. This article describes fundamental studies to highlight and understand such variables, so future experiments can proceed appropriately.


INTRODUCTION

The properties of hair are so dependent on its moisture content, it has been suggested that water should be considered an integral part of its complex structure1,2. Water acts as a plasticizer for hair by solvating electrostatic bonds within the protein structure. The water content of hair is overwhelmingly dependent on the relative humidity of the surrounding atmosphere and consequently the physical properties of fibers also change substantially with climatic conditions. By means of illustration, Figure 1 shows the Young’s modulus of hair (often equated to “stiffness”) as a function of relative humidity. These changing mechanical properties are behind the ability to create temporary “water-set” hair styles using various heat styling devices; in that the removal of moisture induces additional internal bonding which may be sufficient to anchor hair in a new conformation. However, progressive re-adsorption of moisture from the atmosphere reverses this process and produces reversion or loss of style.
Considerable effort has been dedicated to studying the water content of hair. In part this relates to consumer concerns over ...




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