The research group of Kao Corporation and Assistant Professor Kenichiro Murata of Hokkaido University has succeeded for the first time in the world in directly observing the special water "bound water" on the surface of cotton using the latest method.It was demonstrated that the reason why the wet cotton becomes hard after natural drying is that the water of crystallization on the surface of the cotton holds the single fibers together like an adhesive.
When cotton towels are washed without fabric softener and air-dried, they become glued and hard, which is often seen in everyday life.Regarding this, Kao pays attention to water called water of crystallization that is bound to a substance. In 2011, we proposed a model in which this special water develops hardness by binding (cross-linking) single fibers to each other by capillary adhesion (adhesion phenomenon due to liquid intervention between narrow solid surfaces).However, there were many unclear points about the mechanism.
Therefore, this time, with the cooperation and guidance of Assistant Professor Murata of Hokkaido University, we conducted research for the purpose of demonstrating this model from a direct and microscopic (molecular level) perspective.As a result, by using an atomic force microscope (AFM) that can observe the surface of the substance with atomic force level accuracy, bound water exists on the cotton surface, and the viscous bound water is involved in the capillary adhesion between the single fibers. Was shown.In addition, observations by AFM infrared spectroscopy (AFM-IR), which is a state-of-the-art surface analysis method using infrared rays, show that the bound water on the cotton surface exists in two different states, and each of them has an interface with air.・ It was considered that it corresponds to the bound water at the interface with cotton.
The results of this research proved the model proposed by Kao.This gives us a new perspective on the mechanism of the effect manifestation of fabric softeners, and is a clue to understanding the structure and function of water on the surface of substances, which has been the subject of much debate in recent years.
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